Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


Independent Submission H. Spencer Request for Comments: 1849 SP Systems Obsoleted by: 5536, 5537 March 2010 Category: Historic ISSN: 2070-1721

        "Son of 1036": News Article Format and Transmission


 By the early 1990s, it had become clear that RFC 1036, then the
 specification for the Interchange of USENET Messages, was badly in
 need of repair.  This "Internet-Draft-to-be", though never formally
 published at that time, was widely circulated and became the de facto
 standard for implementors of News Servers and User Agents, rapidly
 acquiring the nickname "Son of 1036".  Indeed, under that name, it
 could fairly be described as the best-known Internet Draft (n)ever
 published, and it formed the starting point for the recently adopted
 Proposed Standards for Netnews.
 It is being published now in order to provide the historical
 background out of which those standards have grown.  Present-day
 implementors should be aware that it is NOT NOW APPROPRIATE for use
 in current implementations.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
  published for the historical record.
 This document defines a Historic Document for the Internet community.
 This is a contribution to the RFC Series, independently of any other
 RFC stream.  The RFC Editor has chosen to publish this document at
 its discretion and makes no statement about its value for
 implementation or deployment.  Documents approved for publication by
 the RFC Editor are not a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at

Spencer Historic [Page 1] RFC 1849 Son of 1036 March 2010

Copyright Notice

 Copyright (c) 2010 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 ( in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.
 This document may not be modified, and derivative works of it may not
 be created, except to format it for publication as an RFC or to
 translate it into languages other than English.

Spencer Historic [Page 2] RFC 1849 Son of 1036 March 2010

Table of Contents

 Preface ............................................................5
 Original Abstract ..................................................6
 1. Introduction ....................................................6
 2. Definitions, Notations, and Conventions .........................8
    2.1. Textual Notations ..........................................8
    2.2. Syntax Notation ............................................9
    2.3. Definitions ...............................................10
    2.4. End-of-Line ...............................................13
    2.5. Case-Sensitivity ..........................................13
    2.6. Language ..................................................13
 3. Relation to MAIL (RFC822, etc.) ................................14
 4. Basic Format ...................................................15
    4.1. Overall Syntax ............................................15
    4.2. Headers ...................................................16
         4.2.1. Names and Contents .................................16
         4.2.2. Undesirable Headers ................................18
         4.2.3. White Space and Continuations ......................18
    4.3. Body ......................................................19
         4.3.1. Body Format Issues .................................19
         4.3.2. Body Conventions ...................................20
    4.4. Characters and Character Sets .............................23
    4.5. Non-ASCII Characters in Headers ...........................26
    4.6. Size Limits ...............................................28
    4.7. Example ...................................................30
 5. Mandatory Headers ..............................................30
    5.1. Date ......................................................31
    5.2. From ......................................................33
    5.3. Message-ID ................................................35
    5.4. Subject ...................................................36
    5.5. Newsgroups ................................................38
    5.6. Path ......................................................42
 6. Optional Headers ...............................................45
    6.1. Followup-To ...............................................45
    6.2. Expires ...................................................46
    6.3. Reply-To ..................................................47
    6.4. Sender ....................................................47
    6.5. References ................................................48
    6.6. Control ...................................................50
    6.7. Distribution ..............................................51
    6.8. Keywords ..................................................52
    6.9. Summary ...................................................53
    6.10. Approved .................................................53
    6.11. Lines ....................................................54
    6.12. Xref .....................................................55
    6.13. Organization .............................................56
    6.14. Supersedes ...............................................57

Spencer Historic [Page 3] RFC 1849 Son of 1036 March 2010

    6.15. Also-Control .............................................57
    6.16. See-Also .................................................58
    6.17. Article-Names ............................................58
    6.18. Article-Updates ..........................................60
 7. Control Messages ...............................................60
    7.1. cancel ....................................................61
    7.2. ihave, sendme .............................................64
    7.3. newgroup ..................................................66
    7.4. rmgroup ...................................................68
    7.5. sendsys, version, whogets .................................68
    7.6. checkgroups ...............................................73
 8. Transmission Formats ...........................................74
    8.1. Batches ...................................................74
    8.2. Encoded Batches ...........................................75
    8.3. News within Mail ..........................................76
    8.4. Partial Batches ...........................................77
 9. Propagation and Processing .....................................77
    9.1. Relayer General Issues ....................................78
    9.2. Article Acceptance and Propagation ........................80
    9.3. Administrator Contact .....................................82
 10. Gatewaying ....................................................83
    10.1. General Gatewaying Issues ................................83
    10.2. Header Synthesis .........................................85
    10.3. Message ID Mapping .......................................86
    10.4. Mail to and from News ....................................88
    10.5. Gateway Administration ...................................89
 11. Security and Related Issues ...................................90
    11.1. Leakage ..................................................90
    11.2. Attacks ..................................................91
    11.3. Anarchy ..................................................92
    11.4. Liability ................................................92
 12. References ....................................................93
 Appendix A. Archaeological Notes ..................................96
    A.1. "A News" Article Format ...................................96
    A.2. Early "B News" Article Format .............................96
    A.3. Obsolete Headers ..........................................97
    A.4. Obsolete Control Messages .................................97
 Appendix B. A Quick Tour of MIME ..................................98
 Appendix C. Summary of Changes Since RFC 1036 ....................103
 Appendix D. Summary of Completely New Features ...................104
 Appendix E. Summary of Differences from RFCs 822 and 1123.........105

Spencer Historic [Page 4] RFC 1849 Son of 1036 March 2010


 Although [RFC1036] was published in 1987, for many years it remained
 the only formally published specification for Netnews format and
 processing.  It was widely considered obsolete within a few years,
 and it has now been superseded by the work of the USEFOR Working
 Group, leading to the publication of [RFC5536] and [RFC5537].
 However, there was an intermediate step that is of some historical
 In 1993-4, Henry Spencer wrote and informally circulated a document
 that became known as "Son of 1036", meant as a first draft of a
 replacement for [RFC1036].  It went no further at the time (although,
 more recently, the USEFOR Working Group started from it), but has
 nevertheless seen considerable use as a technical reference and even
 a de facto standard, despite its informal status.
 The USEFOR work has eliminated any further relevance of Son of 1036
 as a technical reference, but it remains of historical interest.  The
 USEFOR Working Group has asked that it be published as an Historic
 RFC, to ensure its preservation in an accessible form and facilitate
 referencing it.
 This document is identical to the last distributed version of Son of
 1036, dated 2 June 1994, except for reformatting, correction of a few
 minor factual or formatting errors, completion of the then-empty
 Appendix D and of the References section, minor editing to match
 preferred RFC style, and changes to leading and trailing material.
 Remarks enclosed within "{...}" indicate explanatory material not
 present in the original version.  References to the current MIME
 standards (and a few others) have been added (that was an unresolved
 issue in 1994).
 The technical content remains unchanged, including the references to
 the document itself as a Draft rather than an RFC and the presence of
 unresolved issues.  The original section numbering has been
 preserved, although the original pagination has not (among other
 reasons, it did not fully follow IETF formatting standards).
 BE USED AS A TECHNICAL REFERENCE.  Although Son of 1036 largely
 documented existing practice, it also proposed some changes, some of
 which did not catch on or are no longer considered good ideas.  (Of
 particular note, the MIME type "message/news" should not be used.)
 Consult [RFC5536] and [RFC5537] for modern technical information.

Spencer Historic [Page 5] RFC 1849 Son of 1036 March 2010

 Although a number of people contributed useful comments or criticism
 during the preparation of this document, its contents are entirely
 the opinions of the author circa 1994.  Not even the author himself
 agrees with them all now.
 The author thanks Charles Lindsey for his assistance in getting this
 document cleaned up and formally published at last (not least, for
 supplying some prodding to actually get it done!).
 The author thanks Luc Rooijakkers for supplying the MIME summary that
 Appendix B is based on.

Original Abstract

 This Draft defines the format and procedures for interchange of
 network news articles.  It is hoped that a later version of this
 Draft will obsolete RFC 1036, reflecting more recent experience and
 accommodating future directions.
 Network news articles resemble mail messages but are broadcast to
 potentially large audiences, using a flooding algorithm that
 propagates one copy to each interested host (or group thereof),
 typically stores only one copy per host, and does not require any
 central administration or systematic registration of interested
 users.  Network news originated as the medium of communication for
 Usenet, circa 1980.  Since then, Usenet has grown explosively, and
 many Internet sites participate in it.  In addition, the news
 technology is now in widespread use for other purposes, on the
 Internet and elsewhere.
 This Draft primarily codifies and organizes existing practice.  A few
 small extensions have been added in an attempt to solve problems that
 are considered serious.  Major extensions (e.g., cryptographic
 authentication) that need significant development effort are left to
 be undertaken as independent efforts.

1. Introduction

 Network news articles resemble mail messages but are broadcast to
 potentially large audiences, using a flooding algorithm that
 propagates one copy to each interested host (or groups thereof),
 typically stores only one copy per host, and does not require any
 central administration or systematic registration of interested
 users.  Network news originated as the medium of communication for
 Usenet, circa 1980.  Since then, Usenet has grown explosively, and
 many Internet sites participate in it.  In addition, the news
 technology is now in widespread use for other purposes, on the
 Internet and elsewhere.

Spencer Historic [Page 6] RFC 1849 Son of 1036 March 2010

 The earliest news interchange used the so-called "A News" article
 format.  Shortly thereafter, an article format vaguely resembling
 Internet mail was devised and used briefly.  Both of those formats
 are completely obsolete; they are documented in Appendix A for
 historical reasons only.  With the publication of [RFC850] in 1983,
 news articles came to closely resemble Internet mail messages, with
 some restrictions and some additional headers.  In 1987, [RFC1036]
 updated [RFC850] without making major changes.
 In the intervening five years, the [RFC1036] article format has
 proven quite satisfactory, although minor extensions appear desirable
 to match recent developments in areas such as multi-media mail.
 [RFC1036] itself has not proven quite so satisfactory.  It is often
 rather vague and does not address some issues at all; this has caused
 significant interoperability problems at times, and implementations
 have diverged somewhat.  Worse, although it was intended primarily to
 document existing practice, it did not precisely match existing
 practice even at the time it was published, and the deviations have
 grown since.
 This Draft attempts to specify the format of articles, and the
 procedures used to exchange them and process them, in sufficient
 detail to allow full interoperability.  In addition, some tentative
 suggestions are made about directions for future development, in an
 attempt to avert unnecessary divergence and consequent loss of
 interoperability.  Major extensions (e.g., cryptographic
 authentication) that need significant development effort are left to
 be undertaken as independent efforts.
    NOTE: One question all of this may raise is: why is there no News-
    Version header, analogous to MIME-Version, specifying a version
    number corresponding to this specification?  The answer is: it
    doesn't appear to be useful, given news's backward-compatibility
    constraints.  The major use of a version number is indicating
    which of several INCOMPATIBLE interpretations is relevant.  The
    impossibility of orchestrating any sort of simultaneous change
    over news's installed base makes it necessary to avoid such
    incompatible changes (as opposed to extensions) entirely.  MIME
    has a version number mostly because it introduced incompatible
    changes to the interpretation of several "Content-" headers.  This
    Draft attempts no changes in interpretation, and it appears
    doubtful that future Drafts will find it feasible to introduce
    UNRESOLVED ISSUE: Should this be reconsidered?  Only if the header
    has SPECIFIC IDENTIFIABLE uses today.  Otherwise, it's just
    useless added bulk.

Spencer Historic [Page 7] RFC 1849 Son of 1036 March 2010

 As in this Draft's predecessors, the exact means used to transmit
 articles from one host to another is not specified.  Network News
 Transfer Protocol (NNTP) [RFC977] {since replaced by [RFC3977]} is
 probably the most common transmission method on the Internet, but a
 number of others are known to be in use, including the Unix-To-Unix
 Copy Protocol [UUCP], which was extensively used in the early days of
 Usenet and is still much used on its fringes today.
 Several of the mechanisms described in this Draft may seem somewhat
 strange or even bizarre at first reading.  As with Internet mail,
 there is no reasonable possibility of updating the entire installed
 base of news software promptly, so interoperability with old software
 is crucial and will remain so.  Compatibility with existing practice
 and robustness in an imperfect world necessarily take priority over

2. Definitions, Notations, and Conventions

2.1. Textual Notations

 Throughout this Draft, "MAIL" is short for "[RFC822] as amended by
 [RFC1123]".  ([RFC1123]'s amendments are mostly relatively small, but
 they are not insignificant.)  See also the discussion in Section 3
 about this Draft's relationship to MAIL.  "MIME" is short for
 "[RFC1341] and [RFC1342]" (or their {since} updated replacements
 {[RFC2045], [RFC2046], and [RFC2047]}).
    UNRESOLVED ISSUE: Update these numbers {now resolved!}.
    {NOTE: Since the original publication of this Draft [RFC822] has
    been updated, firstly to [RFC2822] and more recently to [RFC5322];
    however, this Draft is firmly rooted in the original [RFC822].
    Similarly, [RFC821] has also received two upgrades in the
 "ASCII" is short for "the ANSI X3.4 character set" [X3.4].  While
 "ASCII" is often misused to refer to various character sets somewhat
 similar to X3.4, in this Draft, "ASCII" means [X3.4] and only [X3.4].
    NOTE: The name is traditional (to the point where the ANSI
    standard sanctions it), even though it is no longer an acronym for
    the name of the standard.
    NOTE: ASCII, X3.4, contains 128 characters, not all of them
    printable.  Character sets with more characters are not ASCII,
    although they may include it as a subset.

Spencer Historic [Page 8] RFC 1849 Son of 1036 March 2010

 Certain words used to define the significance of individual
 requirements are capitalized.  "MUST" means that the item is an
 absolute requirement of the specification.  "SHOULD" means that the
 item is a strong recommendation: there may be valid reasons to ignore
 it in unusual circumstances, but this should be done only after
 careful study of the full implications and a firm conclusion that it
 is necessary, because there are serious disadvantages to doing so.
 "MAY" means that the item is truly optional, and implementors and
 users are warned that conformance is possible but not to be relied
 The term "compliant", applied to implementations, etc., indicates
 satisfaction of all relevant "MUST" and "SHOULD" requirements.  The
 term "conditionally compliant" indicates satisfaction of all relevant
 "MUST" requirements but violation of at least one relevant "SHOULD"
 This Draft contains explanatory notes using the following format.
 These may be skipped by persons interested solely in the content of
 the specification.  The purpose of the notes is to explain why
 choices were made, to place them in context, or to suggest possible
 implementation techniques.
    NOTE: While such explanatory notes may seem superfluous in
    principle, they often help the less-than-omniscient reader grasp
    the purpose of the specification and the constraints involved.
    Given the limitations of natural language for descriptive
    purposes, this improves the probability that implementors and
    users will understand the true intent of the specification in
    cases where the wording is not entirely clear.
 All numeric values are given in decimal unless otherwise indicated.
 Octets are assumed to be unsigned values for this purpose.  Large
 numbers are written using the North American convention, in which ","
 separates groups of three digits but otherwise has no significance.

2.2. Syntax Notation

 Although the mechanisms specified in this Draft are all described in
 prose, most are also described formally in the modified BNF notation
 of [RFC822].  Implementors will need to be familiar with this
 notation to fully understand this specification and are referred to
 [RFC822] for a complete explanation of the modified BNF notation.
 Here is a brief illustrative example:

Spencer Historic [Page 9] RFC 1849 Son of 1036 March 2010

    sentence  = clause *( punct clause ) "."
    punct     = ":" / ";"
    clause    = 1*word [ "(" clause ")" / "," 1*word ]
    word      = <any English word>
 This defines a sentence as some clauses separated by puncts and ended
 by a period, a punct as a colon or semicolon, a clause as at least
 one <word> optionally followed by either a parenthesized clause or a
 comma and at least one more <word>, and a <word> as (informally) any
 English word.  The characters "<>" are used to enclose names when
 (and only when) distinguishing them from surrounding text is useful.
 The full form of the repetition notation is "<m>*<n><thing>",
 denoting <m> through <n> repetitions of <thing>; <m> defaults to
 zero, <n> to infinity, and the "*" and <n> can be omitted if <m> and
 <n> are equal, so 1*word is one or more words, 1*5word is one through
 five words, and 2word is exactly two words.
 The character "\" is not special in any way in this notation.
 This Draft is intended to be self-contained; all syntax rules used in
 it are defined within it, and a rule with the same name as one found
 in MAIL does not necessarily have the same definition.  The lexical
 layer of MAIL is NOT, repeat NOT, used in this Draft, and its
 presence must not be assumed; notably, this Draft spells out all
 places where white space is permitted/required and all places where
 constructs resembling MAIL comments can occur.
    NOTE: News parsers historically have been much less permissive
    than MAIL parsers.

2.3. Definitions

 The term "character set", wherever it is used in this Draft, refers
 to a coded character set, in the sense of ISO character set
 standardization work, and must not be misinterpreted as meaning
 merely "a set of characters".
 In this Draft, ASCII character 32 is referred to as "blank"; the word
 "space" has a more generic meaning.
 An "article" is the unit of news, analogous to a MAIL "message".
 A "poster" is a human being (or software equivalent) submitting a
 possibly compliant article to be "posted", i.e., made available for
 reading on all relevant hosts.  A "posting agent" is software that
 assists posters to prepare articles, including determining whether
 the final article is compliant, passing it on to a relayer for
 posting if so, and returning it to the poster with an explanation if

Spencer Historic [Page 10] RFC 1849 Son of 1036 March 2010

 not.  A "relayer" is software that receives allegedly compliant
 articles from posting agents and/or other relayers, files copies in a
 "news database", and possibly passes copies on to other relayers.
    NOTE: While the same software may well function both as a relayer
    and as part of a posting agent, the two functions are distinct and
    should not be confused.  The posting agent's purpose is (in part)
    to validate an article, supply header information that can or
    should be supplied automatically, and generally take reasonable
    actions in an attempt to transform the poster's submission into a
    compliant article.  The relayer's purpose is to move already-
    compliant articles around efficiently without damaging them.
 A "reader" is a human being reading news articles.  A "reading agent"
 is software that presents articles to a reader.
    NOTE: Informal usage often uses "reader" for both these meanings,
    but this introduces considerable potential for confusion and
    misunderstanding, so this Draft takes care to make the
 A "newsgroup" is a single news forum, a logical bulletin board,
 having a name and nominally intended for articles on a specific
 topic.  An article is "posted to" a single newsgroup or several
 newsgroups.  When an article is posted to more than one newsgroup, it
 is said to be "cross-posted"; note that this differs from posting the
 same text as part of each of several articles, one per newsgroup.  A
 "hierarchy" is the set of all newsgroups whose names share a first
 component (see the name syntax in Section 5.5).
 A newsgroup may be "moderated", in which case submissions are not
 posted directly, but mailed to a "moderator" for consideration and
 possible posting.  Moderators are typically human but may be
 implemented partially or entirely in software.
 A "followup" is an article containing a response to the contents of
 an earlier article (the followup's "precursor").  A "followup agent"
 is a combination of reading agent and posting agent that aids in the
 preparation and posting of a followup.
 Text comparisons are "case-sensitive" if they consider uppercase
 letters (e.g., "A") different from lowercase letters (e.g., "a"), and
 "case-insensitive" if letters differing only in case (e.g., "A" and
 "a") are considered identical.  Categories of text are said to be
 case-(in)sensitive if comparisons of such texts to others are case-

Spencer Historic [Page 11] RFC 1849 Son of 1036 March 2010

 A "cooperating subnet" is a set of news-exchanging hosts that is
 sufficiently well-coordinated (typically via a central administration
 of some sort) that stronger assumptions can be made about hosts in
 the set than about news hosts in general.  This is typically used to
 relax restrictions that are otherwise required for worst-case
 interoperability; members of a cooperating subnet MAY interchange
 articles that do not conform to this Draft's specifications, provided
 all members have agreed to this and provided the articles are not
 permitted to leak out of the subnet.  The word "subnet" is used to
 emphasize that a cooperating subnet is typically not an isolated
 universe; care must be taken that traffic leaving the subnet complies
 with the restrictions of the larger net, not just those of the
 cooperating subnet.
 A "message ID" is a unique identifier for an article, usually
 supplied by the posting agent that posted it.  It distinguishes the
 article from every other article ever posted anywhere (in theory).
 Articles with the same message ID are treated as identical copies of
 the same article even if they are not in fact identical.
 A "gateway" is software that receives news articles and converts them
 to messages of some other kind (e.g., mail to a mailing list), or
 vice versa; in essence, it is a translating relayer that straddles
 boundaries between different methods of message exchange.  The most
 common type of gateway connects newsgroup(s) to mailing list(s),
 either unidirectionally or bidirectionally, but there are also
 gateways between news networks using this Draft's news format and
 those using other formats.
 A "control message" is an article that is marked as containing
 control information; a relayer receiving such an article will
 (subject to permissions, etc.) take actions beyond just filing and
 passing on the article.
    NOTE: "Control article" would be more consistent terminology, but
    "control message" is already well established.
 An article's "reply address" is the address to which mailed replies
 should be sent.  This is the address specified in the article's From
 header (see Section 5.2), unless it also has a Reply-To header (see
 Section 6.3).
 The notation (for example) "(ASCII 17)" following a name means "this
 name refers to the ASCII character having value 17".  An "ASCII
 printable character" is an ASCII character in the range 33-126.  An
 "ASCII control character" is an ASCII character in the range 0-31, or
 the character DEL (ASCII 127).  A "non-ASCII character" is a
 character having a value exceeding 127.

Spencer Historic [Page 12] RFC 1849 Son of 1036 March 2010

    NOTE: Blank is neither an "ASCII printable character" nor an
    "ASCII control character".

2.4. End-of-Line

 How the end of a text line is represented depends on the context and
 the implementation.  For Internet transmission via protocols such as
 SMTP [RFC821], an end-of-line is a CR (ASCII 13) followed by an LF
 (ASCII 10).  ISO C [ISO/IEC9899] and many modern operating systems
 indicate end-of-line with a single character, typically ASCII LF (aka
 "newline"), and this is the normal convention when news is
 transmitted via UUCP.  A variety of other methods are in use,
 including out-of-band methods in which there is no specific character
 that means end-of-line.
 This Draft does not constrain how end-of-line is represented in news,
 except that characters other than CR and LF MUST NOT be usurped for
 use in end-of-line representations.  Also, obviously, all software
 dealing with a particular copy of an article must agree on the
 convention to be used.  "EOL" is used to mean "whatever end-of-line
 representation is appropriate"; it is not necessarily a character or
 sequence of characters.
    NOTE: If faced with picking an EOL representation in the absence
    of other constraints, use of a single character simplifies
    processing, and the ASCII standard [X3.4] specifies that if one
    character is to be used for this purpose, it should be LF (ASCII
    NOTE: Inside MIME encodings, use of the Internet canonical EOL
    representation (CR followed by LF) is mandatory.  See [RFC2049].

2.5. Case-Sensitivity

 Text in newsgroup names, header parameters, etc. is case-sensitive
 unless stated otherwise.
    NOTE: This is at variance with MAIL, which is case-insensitive
    unless stated otherwise, but is consistent with news historical
    practice and existing news software.  See the comments on backward
    compatibility in Section 1.

2.6. Language

 Various constant strings in this Draft, such as header names and
 month names, are derived from English words.  Despite their
 derivation, these words do NOT change when the poster or reader
 employing them is interacting in a language other than English.

Spencer Historic [Page 13] RFC 1849 Son of 1036 March 2010

 Posting and reading agents SHOULD translate as appropriate in their
 interaction with the poster or reader, but the forms that actually
 appear in articles are always the English-derived ones defined in
 this Draft.

3. Relation to MAIL (RFC822, etc.)

 The primary intent of this Draft is to completely describe the news
 article format as a subset of MAIL's message format (augmented by
 some new headers).  Unless explicitly noted otherwise, the intent
 throughout is that an article MUST also be a valid MAIL message.
    NOTE: Despite obvious similarities between news and mail, opinions
    vary on whether it is possible or desirable to unify them into a
    single service.  However, it is unquestionably both possible and
    useful to employ some of the same tools for manipulating both mail
    messages and news articles, so there is specific advantage to be
    had in defining them compatibly.  Furthermore, there is no
    apparent need to re-invent the wheel when slight extensions to an
    existing definition will suffice.
 Given that this Draft attempts to be self-contained, it inevitably
 contains considerable repetition of information found in MAIL.  This
 raises the possibility of unintentional conflicts.  Unless
 specifically noted otherwise, any wording in this Draft that permits
 behavior that is not MAIL-compliant is erroneous and should be
 followed only to the extent that the result remains compliant with
    NOTE: [RFC1036] said "where this standard conflicts with the
    Internet Standard, RFC 822 should be considered correct and this
    standard in error".  Taken literally, this was obviously
    incorrect, since [RFC1036] imposed a number of restrictions not
    found in [RFC822].  The intent, however, was reasonable: to
    indicate that UNINTENTIONAL differences were errors in [RFC1036].
 Implementors and users should note that MAIL is deliberately an
 extensible standard, and most extensions devised for mail are also
 relevant to (and compatible with) news.  Note particularly MIME,
 summarized briefly in Appendix B, which extends MAIL in a number of
 useful ways that are definitely relevant to news.  Also of note is
 the work in progress on reconciling Privacy Enhanced Mail (PEM),
 which defines extensions for authentication and security) with MIME,
 after which this may also be relevant to news.
    UNRESOLVED ISSUE: Update the MIME/PEM information.

Spencer Historic [Page 14] RFC 1849 Son of 1036 March 2010

 Similarly, descriptions here of MIME facilities should be considered
 correct only to the extent that they do not require or legitimize
 practices that would violate those RFCs.  (Note that this Draft does
 extend the application of some MIME facilities, but this is an
 extension rather than an alteration.)

4. Basic Format

4.1. Overall Syntax

 The overall syntax of a news article is:
    article         = 1*header separator body
    header          = start-line *continuation
    start-line      = header-name ":" space [ nonblank-text ] eol
    continuation    = space nonblank-text eol
    header-name     = 1*name-character *( "-" 1*name-character )
    name-character  = letter / digit
    letter          = <ASCII letter A-Z or a-z>
    digit           = <ASCII digit 0-9>
    separator       = eol
    body            = *( [ nonblank-text / space ] eol )
    eol             = <EOL>
    nonblank-text   = [ space ] text-character *( space-or-text )
    text-character  = <any ASCII character except NUL (ASCII 0),
                        HT (ASCII 9), LF (ASCII 10), CR (ASCII 13),
                        or blank (ASCII 32)>
    space           = 1*( <HT (ASCII 9)> / <blank (ASCII 32)> )
    space-or-text   = space / text-character
 An article consists of some headers followed by a body.  An empty
 line separates the two.  The headers contain structured information
 about the article and its transmission.  A header begins with a
 header name identifying it, and can be continued onto subsequent
 lines by beginning the continuation line(s) with white space.  (Note
 that Section 4.2.3 adds some restrictions to the header syntax
 indicated here.)  The body is largely unstructured text significant
 only to the poster and the readers.
    NOTE: Terminology here follows the current custom in the news
    community, rather than the MAIL convention of (sometimes)
    referring to what is here called a "header" as a "header field" or
 Note that the separator line must be truly empty, and not just a line
 containing white space.  Further empty lines following it are part of
 the body, as are empty lines at the end of the article.

Spencer Historic [Page 15] RFC 1849 Son of 1036 March 2010

    NOTE: Some systems make no distinction between empty lines and
    lines consisting entirely of white space; indeed, some systems
    cannot represent entirely empty lines.  The grammar's requirement
    that header continuation lines contain some printable text is
    meant to ensure that the empty/space distinction cannot confuse
    identification of the separator line.
    NOTE: It is tempting to authorize posting agents to strip empty
    lines at the beginning and end of the body, but such empty lines
    could possibly be part of a preformatted document.
 Implementors are warned that trailing white space, whether alone on
 the line or not, MAY be significant in the body, notably in early
 versions of the "uuencode" encoding for binary data.  Trailing white
 space MUST be preserved unless the article is known to have
 originated within a cooperating subnet that avoids using significant
 trailing white space, and SHOULD be preserved regardless.  Posters
 SHOULD avoid using conventions or encodings that make trailing white
 space significant; for encoding of binary data, MIME's "base64"
 encoding is recommended.  Implementors are warned that ISO C
 implementations are not required to preserve trailing white space,
 and special precautions may be necessary in implementations that do
    NOTE: Unfortunately, the signature-delimiter convention (described
    in Section 4.3.2) does use significant trailing white space.  It's
    too late to fix this; there is work underway on defining an
    organized signature convention as part of MIME, which is a
    preferable solution in the long run.
 Posters are warned that some very old relayer software misbehaves
 when the first non-empty line of an article body begins with white

4.2. Headers

4.2.1. Names and Contents

 Despite the restrictions on header-name syntax imposed by the
 grammar, relayers and reading agents SHOULD tolerate header names
 containing any ASCII printable character other than colon (":",
 ASCII 58).
    NOTE: MAIL header names can contain any ASCII printable character
    (other than colon) in theory, but in practice, arbitrary header
    names are known to cause trouble for some news software.  Section
    4.1's restriction to alphanumeric sequences separated by hyphens
    is believed to permit all widely used header names without causing

Spencer Historic [Page 16] RFC 1849 Son of 1036 March 2010

    problems for any widely used software.  Software is nevertheless
    encouraged to cope correctly with the full range of possibilities,
    since aberrations are known to occur.
 Relayers MUST disregard headers not described in this Draft (that is,
 with header names not mentioned in this Draft) and pass them on
 Posters wishing to convey non-standard information in headers SHOULD
 use header names beginning with "X-".  No standard header name will
 ever be of this form.  Reading agents SHOULD ignore "X-" headers, or
 at least treat them with great care.
 The order of headers in an article is not significant.  However,
 posting agents are encouraged to put mandatory headers (see
 Section 5) first, followed by optional headers (see Section 6),
 followed by headers not defined in this Draft.
    NOTE: While relayers and reading agents must be prepared to handle
    any order, having the significant headers (the precise definition
    of "significant" depends on context) first can noticeably improve
    efficiency, especially in memory-limited environments where it is
    difficult to buffer up an arbitrary quantity of headers while
    searching for the few that matter.
 Header names are case-insensitive.  There is a preferred case
 convention, which posters and posting agents SHOULD use: each hyphen-
 separated "word" has its initial letter (if any) in uppercase and the
 rest in lowercase, except that some abbreviations have all letters
 uppercase (e.g., "Message-ID" and "MIME-Version").  The forms used in
 this Draft are the preferred forms for the headers described herein.
 Relayers and reading agents are warned that articles might not obey
 this convention.
    NOTE: Although software must be prepared for the possibility of
    random use of case in header names (and other case-independent
    text), establishing a preferred convention reduces pointless
    diversity and may permit optimized software that looks for the
    preferred forms before resorting to less-efficient case-
    insensitive searches.
 In general, a header can consist of several lines, with each
 continuation line beginning with white space.  The EOLs preceding
 continuation lines are ignored when processing such a header,
 effectively combining the start-line and the continuations into a
 single logical line.  The logical line, less the header name, colon,
 and any white space following the colon, is the "header content".

Spencer Historic [Page 17] RFC 1849 Son of 1036 March 2010

4.2.2. Undesirable Headers

 A header whose content is empty is said to be an empty header.
 Relayers and reading agents SHOULD NOT consider presence or absence
 of an empty header to alter the semantics of an article (although
 syntactic rules, such as requirements that certain header names
 appear at most once in an article, MUST still be satisfied).  Posting
 agents SHOULD delete empty headers from articles before posting them.
 Headers that merely state defaults explicitly (e.g., a Followup-To
 header with the same content as the Newsgroups header, or a MIME
 Content-Type header with contents "text/plain; charset=us-ascii") or
 state information that reading agents can typically determine easily
 themselves (e.g., the length of the body in octets) are redundant,
 conveying no information whatsoever.  Headers that state information
 that cannot possibly be of use to a significant number of relayers,
 reading agents, or readers (e.g., the name of the software package
 used as the posting agent) are useless and pointless.  Posters and
 posting agents SHOULD avoid including redundant or useless headers in
    NOTE: Information that someone, somewhere, might someday find
    useful is best omitted from headers.  (There's quite enough of it
    in article bodies.)  Headers should contain information of known
    utility only.  This is not meant to preclude inclusion of
    information primarily meant for news-software debugging, but such
    information should be included only if there is real reason,
    preferably based on experience, to suspect that it may be
    genuinely useful.  Articles passing through gateways are the only
    obvious case where inclusion of debugging information appears
    clearly legitimate.  (See Section 10.1.)
    NOTE: A useful rule of thumb for software implementors is: "if I
    had to pay a dollar a day for the transmission of this header,
    would I still think it worthwhile?".

4.2.3. White Space and Continuations

 The colon following the header name on the start-line MUST be
 followed by white space, even if the header is empty.  If the header
 is not empty, at least some of the content MUST appear on the start-
 line.  Posting agents MUST enforce these restrictions, but relayers
 (etc.) SHOULD accept even articles that violate them.
    NOTE: MAIL does not require white space after the colon, but it is
    usual. [RFC1036] required the white space, even in empty headers,
    and some existing software demands it.  In MAIL, and arguably in
    [RFC1036] (although the wording is vague), it is technically

Spencer Historic [Page 18] RFC 1849 Son of 1036 March 2010

    legitimate for the white space to be part of a continuation line
    rather than the start-line, but not all existing software will
    accept this.  Deleting empty headers and placing some content on
    the start-line avoids this issue; this is desirable because
    trailing blanks, easily deleted by accident, are best not made
    significant in headers.
 In general, posters and posting agents SHOULD use blank (ASCII 32),
 not tab (ASCII 9), where white space is desired in headers.  Existing
 software does not consistently accept tab as synonymous with blank in
 all contexts.  In particular, [RFC1036] appeared to specify that the
 character immediately following the colon after a header name was
 required to be a blank, and some news software insists on that, so
 this character MUST be a blank.  Again, posting agents MUST enforce
 these restrictions but relayers SHOULD be more tolerant.
 Since the white space beginning a continuation line remains a part of
 the logical line, headers can be "broken" into multiple lines only at
 white space.  Posting agents SHOULD NOT break headers unnecessarily.
 Relayers SHOULD preserve existing header breaks, and SHOULD NOT
 introduce new breaks.  Breaking headers SHOULD be a last resort;
 relayers and reading agents SHOULD handle long header lines
 gracefully.  (See the discussion of size limits in Section 4.6.)

4.3. Body

 Although the article body is unstructured for most of the purposes of
 this Draft, structure MAY be imposed on it by other means, notably
 MIME headers (see Appendix B).

4.3.1. Body Format Issues

 The body of an article MAY be empty, although posting agents SHOULD
 consider this an error condition (meriting returning the article to
 the poster for revision).  A posting agent that does not reject such
 an article SHOULD issue a warning message to the poster and supply a
 non-empty body.  Note that the separator line MUST be present even if
 the body is empty.
    NOTE: An empty body is probably a poster error except, arguably,
    for some control messages, and even they really ought to have a
    body explaining the reason for the control message.  Some old
    reading agents are known to generate empty bodies for "cancel"
    control messages, so posting agents might opt not to reject
    bodyless articles in such cases (although it would be better to
    fix the reading agents to request a body).  However, some existing
    news software is known to react badly to bodyless articles, hence
    the request for posting agents to insert a body in such cases.

Spencer Historic [Page 19] RFC 1849 Son of 1036 March 2010

    NOTE: A possible posting-agent-supplied body text (already used by
    one widespread posting agent) is "This article was probably
    generated by a buggy news reader".  (The use of "reader" to refer
    to the reading agent is traditional, although this Draft uses more
    precise terminology.)
    NOTE: The requirement for the separator line even in a bodyless
    article is inherited from MAIL and also distinguishes legitimately
    bodyless articles from articles accidentally truncated in the
    middle of the headers.
 Note that an article body is a sequence of lines terminated by EOLs,
 not arbitrary binary data, and in particular it MUST end with an EOL.
 However, relayers SHOULD treat the body of an article as an
 uninterpreted sequence of octets (except as mandated by changes of
 EOL representation and by control-message processing) and SHOULD
 avoid imposing constraints on it.  See also Section 4.6.

4.3.2. Body Conventions

 Although body lines can in principle be very long (see Section 4.6
 for some discussion of length limits), posters SHOULD restrict body
 line lengths to circa 70-75 characters.  On systems where text is
 conventionally stored with EOLs only at paragraph breaks and other
 "hard return" points, with software breaking lines as appropriate for
 display or manipulation, posting agents SHOULD insert EOLs as
 necessary so that posted articles comply with this restriction.
    NOTE: News originated in environments where line breaks in plain
    text files were supplied by the user, not the software.  Be this
    good or bad, much reading-agent and posting-agent software assumes
    that news articles follow this convention, so it is often
    inconvenient to read or respond to articles that violate it.  The
    "70-75" number comes from the widespread use of display devices
    that are 80 columns wide (with the number reduced to provide a bit
    of margin for quoting, see below).
 Reading agents confronted with body lines much longer than the
 available output-device width SHOULD break lines as appropriate.
 Posters are warned that such breaks may not occur exactly where the
 poster intends.
    NOTE: "As appropriate" would typically include breaking lines when
    supplying the text of an article to be quoted in a reply or
    followup, something that line-breaking reading agents often
    neglect to do now.

Spencer Historic [Page 20] RFC 1849 Son of 1036 March 2010

 Although styles vary widely, for plain text it is usual to use no
 left margin, leave the right edge ragged, use a single empty line to
 separate paragraphs, and employ normal natural-language usage on
 matters such as upper/lowercase.  (In particular, articles SHOULD NOT
 be written entirely in uppercase.  In environments where posters have
 access only to uppercase, posting agents SHOULD translate it to
    NOTE: Most people find substantial bodies of text entirely in
    uppercase relatively hard to read, while all-lowercase text merely
    looks slightly odd.  The common association of uppercase with
    strong emphasis adds to this.
 Tone of voice does not carry well in written text, and
 misunderstandings are common when sarcasm, parody, or exaggeration
 for humorous effect is attempted without explicit warning.  It has
 become conventional to use the sequence ":-)", which (on most output
 devices) resembles a rotated "smiley face" symbol, as a marker for
 text not meant to be taken literally, especially when humor is
 intended.  This practice aids communication and averts unintended
 ill-will; posters are urged to use it.  A variety of analogous
 sequences are used with less-standardized meanings [Sanderson].
 The order of arrival of news articles at a particular host depends
 somewhat on transmission paths, and occasionally articles are lost
 for various reasons.  When responding to a previous article, posters
 SHOULD NOT assume that all readers understand the exact context.  It
 is common to quote some of the previous article to establish context.
 This SHOULD be done by prefacing each quoted line (even if it is
 empty) with the character ">".  This will result in multiple levels
 of ">" when quoted context itself contains quoted context.
    NOTE: It may seem superfluous to put a prefix on empty lines, but
    it simplifies implementation of functions such as "skip all quoted
    text" in reading agents.
 Readability is enhanced if quoted text and new text are separated by
 an empty line.
 Posters SHOULD edit quoted context to trim it down to the minimum
 necessary.  However, posting agents SHOULD NOT attempt to enforce
 this by imposing overly simplistic rules like "no more than 50% of
 the lines should be quotes".
    NOTE: While encouraging trimming is desirable, the 50% rule
    imposed by some old posting agents is both inadequate and
    counterproductive.  Posters do not respond to it by being more
    selective about quoting; they respond by padding short responses,

Spencer Historic [Page 21] RFC 1849 Son of 1036 March 2010

    or by using different quoting styles to defeat automatic analysis.
    The former adds unnecessary noise and volume, while the latter
    also defeats more useful forms of automatic analysis that reading
    agents might wish to do.
    NOTE: At the very least, if a minimum-unquoted quota is being set,
    article bodies shorter than (say) 20 lines, or perhaps articles
    that exceed the quota by only a few lines, should be exempt.  This
    avoids the ridiculous situation of complaining about a 5-line
    response to a 6-line quote.
    NOTE: A more subtle posting-agent rule, suggested for experimental
    use, is to reject articles that appear to contain quoted
    signatures (see below).  This is almost certainly the result of a
    careless poster not bothering to trim down quoted context.  Also,
    if a posting agent or followup agent presents an article template
    to the poster for editing, it really should take note of whether
    the poster actually made any changes, and refrain from posting an
    unmodified template.
 Some followup agents supply "attribution" lines for quoted context,
 indicating where it first appeared and under whose name.  When
 multiple levels of quoting are present and quoted context is edited
 for brevity, "inner" attribution lines are not always retained.  The
 editing process is also somewhat error-prone.  Reading agents (and
 readers) are warned not to assume that attributions are accurate.
    UNRESOLVED ISSUE: Should a standard format for attribution lines
    be defined?  There is already considerable diversity, but
    automatic news analysis would be substantially aided by a standard
 Early difficulties in inferring return addresses from article headers
 led to "signatures": short closing texts, automatically added to the
 end of articles by posting agents, identifying the poster and giving
 his network addresses, etc.  If a poster or posting agent does append
 a signature to an article, the signature SHOULD be preceded with a
 delimiter line containing (only) two hyphens (ASCII 45) followed by
 one blank (ASCII 32).  Posting agents SHOULD limit the length of
 signatures, since verbose excess bordering on abuse is common if no
 restraint is imposed; 4 lines is a common limit.
    NOTE: While signatures are arguably a blemish, they are a well-
    understood convention, and conveying the same information in
    headers exposes it to mangling and makes it rather less
    conspicuous.  A standard delimiter line makes it possible for
    reading agents to handle signatures specially if desired.

Spencer Historic [Page 22] RFC 1849 Son of 1036 March 2010

    (This is unfortunately hampered by extensive misunderstanding of,
    and misuse of, the delimiter.)
    NOTE: The choice of delimiter is somewhat unfortunate, since it
    relies on preservation of trailing white space, but it is too
    well-established to change.  There is work underway to define a
    more sophisticated signature scheme as part of MIME, and this will
    presumably supersede the current convention in due time.
    NOTE: Four 75-column lines of signature text is 300 characters,
    which is ample to convey name and mail-address information in all
    but the most bizarre situations.

4.4. Characters and Character Sets

 Header and body lines MAY contain any ASCII characters other than CR
 (ASCII 13), LF (ASCII 10), and NUL (ASCII 0).
    NOTE: CR and LF are excluded because they clash with common EOL
    conventions.  NUL is excluded because it clashes with the C
    end-of-string convention, which is significant to most existing
    news software.  These three characters are unlikely to be
    transmitted successfully.
 However, posters SHOULD avoid using ASCII control characters except
 for tab (ASCII 9), formfeed (ASCII 12), and backspace (ASCII 8).  Tab
 signifies sufficient horizontal white space to reach the next of a
 set of fixed positions; posters are warned that there is no standard
 set of positions, so tabs should be avoided if precise spacing is
 essential.  Formfeed signifies a point at which a reading agent
 SHOULD pause and await reader interaction before displaying further
 text.  Backspace SHOULD be used only for underlining, done by a
 sequence of underscores (ASCII 95) followed by an equal number of
 backspaces, signifying that the same number of text characters
 following are to be underlined.  Posters are warned that underlining
 is not available on all output devices and is best not relied on for
 essential meaning.  Reading agents SHOULD recognize underlining and
 translate it to the appropriate commands for devices that support it.
    NOTE: Interpretation of almost all control characters is device-
    specific to some degree, and devices differ.  Tabs and underlining
    are supported, to some extent, by most modern devices and reading
    agents, hence the cautious exemptions for them.  The underlining
    method is specified because the inverse method, text and then
    underscores, is tempting to the naive; however, if sent unaltered
    to a device that shows only the most recent of several overstruck
    characters rather than a composite, the result can be utterly

Spencer Historic [Page 23] RFC 1849 Son of 1036 March 2010

    NOTE: A common interpretation of tab is that it is a request to
    space forward to the next position whose number is one more than a
    multiple of 8, with positions numbered sequentially starting at 1.
    (So tab positions are 9, 17, 25, ...)  Reading agents not
    constrained by existing system conventions might wish to use this
    NOTE: It will typically be necessary for a reading agent to catch
    and interpret formfeed, not just send it to the output device.
    The actions performed by typical output devices on receiving a
    formfeed are neither adequate for, nor appropriate to, the pause-
    for-interaction meaning.
 Cooperating subnets that wish to employ non-ASCII character sets by
 using escape sequences (employing, e.g., ESC (ASCII 27), SO
 (ASCII 14), and SI (ASCII 15)) to alter the meaning of superficially
 ASCII characters MAY do so, but MUST use MIME headers to alert
 reading agents to the particular character set(s) and escape
 sequences in use.  A reading agent SHOULD NOT pass such an escape
 sequence through, unaltered, to the output device unless the agent
 confirms that the sequence is one used to affect character sets and
 has reason to believe that the device is capable of interpreting that
 particular sequence properly.
    NOTE: Cooperating-subnet organizers are warned that some very old
    relayers strip certain control characters out of articles they
    pass along.  ESC is known to be among the affected characters.
    NOTE: There are now standard Internet encodings for Japanese
    [RFC1345] and Vietnamese [RFC1456] in particular.
 Articles MUST NOT contain any octet with value exceeding 127, i.e.,
 any octet that is not an ASCII character.
    NOTE: This rule, like others, may be relaxed by unanimous consent
    of the members of a cooperating subnet, provided suitable
    precautions are taken to ensure that rule-violating articles do
    not leak out of the subnet.  (This has already been done in many
    areas where ASCII is not adequate for the local language(s).)
    Beware that articles containing non-ASCII octets in headers are a
    violation of the MAIL specifications and are not valid MAIL
    messages.  MIME offers a way to encode non-ASCII characters in
    ASCII for use in headers; see Section 4.5.

Spencer Historic [Page 24] RFC 1849 Son of 1036 March 2010

    NOTE: While there is great interest in using 8-bit character sets,
    not all software can yet handle them correctly, hence the
    restriction to cooperating subnets.  MIME encodings can be used to
    transmit such characters while remaining within the octet
 In anticipation of the day when it is possible to use non-ASCII
 characters safely anywhere, and to provide for the (substantial)
 cooperating subnets that are already using them, transmission paths
 SHOULD treat news articles as uninterpreted sequences of octets
 (except perhaps for transformations between EOL representations) and
 relayers SHOULD treat non-ASCII characters in articles as ordinary
    NOTE: 8-bit enthusiasts are warned that not all software conforms
    to these recommendations yet.  In particular, standard NNTP
    [RFC977] is a 7-bit protocol {but in [RFC3977] it has been upped
    to 8-bit}, and there may be implementations that enforce this
    rule.  Be warned, also, that it will never be safe to send raw
    binary data in the body of news articles, because changes of EOL
    representation may (will!) corrupt it.
 Except where cooperating subnets permit more direct approaches, MIME
 headers and encodings SHOULD be used to transmit non-ASCII content
 using ASCII characters; see Section 4.5, Appendix B, and the MIME
 RFCs for details.  If article content can be expressed in ASCII, it
 SHOULD be.  Failing that, the order of preference for character sets
 is that described in MIME.
    NOTE: Using the MIME facilities, it is possible to transmit ANY
    character set, and ANY form of binary data, using only ASCII
    characters.  Equally important, such articles are self-describing
    and the reading agent can tell which octet-to-symbol mapping is
    intended!  Designation of some preferred character sets is
    intended to minimize the number of character sets that a reading
    agent must understand in order to display most articles properly.
 Articles containing non-ASCII characters, articles using ASCII
 characters (values 0 through 127) to refer to non-ASCII symbols, and
 articles using escape sequences to shift character sets SHOULD
 include MIME headers indicating which character set(s) and
 conventions are being used.  They MUST do so unless such articles are
 strictly confined to a cooperating subnet that has its own pre-agreed
 conventions.  MIME encodings are preferred over all of these
 techniques.  If it comes to a relayer's attention that it is being
 asked to pass an article using such techniques outward across what it
 knows to be the boundary of such a cooperating subnet, it MUST report

Spencer Historic [Page 25] RFC 1849 Son of 1036 March 2010

 this error to its administrator and MAY refuse to pass the article
 beyond the subnet boundary.  If it does pass the article, it MUST
 re-encode it with MIME encodings to make it conform to this Draft.
    NOTE: Such re-encoding is a non-trivial task, due to MIME rules
    such as the prohibition of nested encodings.  It's not just a
    matter of pouring the body through a simple filter.
 Reading agents SHOULD note MIME headers and attempt to show the
 reader the closest possible approximation to the intended content.
 They SHOULD NOT just send the octets of the article to the output
 device unaltered, unless there is reason to believe that the output
 device will indeed interpret them correctly.  Reading agents MUST NOT
 pass ASCII control characters or escape sequences, other than as
 discussed above, unaltered to the output device; only by chance would
 the result be the desired one, and there is serious potential for
 harmful side effects, either accidental or malicious.
    NOTE: Exactly what to do with unwanted control
    characters/sequences depends on the philosophy of the reading
    agent, but passing them straight to the output device is almost
    always wrong.  If the reading agent wants to mark the presence of
    such a character/sequence in circumstances where only ASCII
    printable characters are available, translating it to "#" might be
    a suitable method; "#" is a conspicuous character seldom used in
    normal text.
    NOTE: Reading agents should be aware that many old output devices
    (or the transmission paths to them) zero out the top bit of octets
    sent to them.  This can transform non-ASCII characters into ASCII
    control characters.
 Followup agents MUST be careful to apply appropriate transformations
 of representation to the outbound followup as well as the inbound
 precursor.  A followup to an article containing non-ASCII material is
 very likely to contain non-ASCII material itself.

4.5. Non-ASCII Characters in Headers

 All octets found in headers MUST be ASCII characters.  However, it is
 desirable to have a way of encoding non-ASCII characters, especially
 in "human-readable" headers such as Subject.  MIME provides a way to
 do this.  Full details may be found in the MIME specifications;
 herewith a quick summary to alert software authors to the issues.

Spencer Historic [Page 26] RFC 1849 Son of 1036 March 2010

    encoded-word  = "=?" charset "?" encoding "?" codes "?="
    charset       = 1*tag-char
    encoding      = 1*tag-char
    tag-char      = < ASCII printable character except
                              !()<>@,;:\"[]/?= >
    codes         = 1*code-char
    code-char     = <ASCII printable character except ?>
 An encoded word is a sequence of ASCII printable characters that
 specifies the character set, encoding method, and bits of
 (potentially) non-ASCII characters.  Encoded words are allowed only
 in certain positions in certain headers.  Specific headers impose
 restrictions on the content of encoded words beyond that specified in
 this section.  Posting agents MUST ensure that any material
 resembling an encoded word (complete with all delimiters), in a
 context where encoded words may appear, really is an encoded word.
    NOTE: The syntax is a bit ugly, but it was designed to minimize
    chances of confusion with legitimate header contents, and to
    satisfy difficult constraints on use within existing headers.
 An encoded word MUST NOT be more than 75 octets long.  Each line of a
 header containing encoded word(s) MUST be at most 76 octets long, not
 counting the EOL.
    NOTE: These limits are meant to bound the lookahead needed to
    determine whether text that begins with "=?" is really an encoded
 The details of charsets and encodings are defined by MIME; the
 sequence of preferred character sets is the same as MIME's.  Encoded
 words SHOULD NOT be used for content expressible in ASCII.
 When an encoded word is used, other than in a newsgroup name (see
 Section 5.5), it MUST be separated from any adjacent non-space
 characters (including other encoded words) by white space.  Reading
 agents displaying the contents of encoded words (as opposed to their
 encoded form) should ignore white space adjacent to encoded words.
    UNRESOLVED ISSUE: Should this section be deleted entirely, or made
    much more terse?  The material is relevant, but too complex to
    discuss fully.
    NOTE: The deletion of intervening white space permits using
    multiple encoded words, implicitly concatenated by the deletion,
    to encode text that will not fit within a single 75-character
    encoded word.

Spencer Historic [Page 27] RFC 1849 Son of 1036 March 2010

 Reading-agent implementors are warned that although this Draft
 completely specifies where encoded words may appear in the headers it
 defines, there are other headers (e.g., the MIME Content-Description
 header) that MAY contain them.

4.6. Size Limits

 Implementations SHOULD avoid fixed constraints on the sizes of lines
 within an article and on the size of the entire article.
 Relayers SHOULD treat the body of an article as an uninterpreted
 sequence of octets (except as mandated by changes of EOL
 representation and processing of control messages), not to be altered
 or constrained in any way.
 If it is absolutely necessary for an implementation to impose a limit
 on the length of header lines, body lines, or header logical lines,
 that limit shall be at least 1000 octets, including EOL
 representations.  Relayers and transmission paths confronted with
 lines beyond their internal limits (if any) MUST NOT simply inject
 EOLs at random places; they MAY break headers (as described in
 Section 4.2.3) as a last resort, and otherwise they MUST either pass
 the long lines through unaltered, or refuse to pass the article at
 all (see Section 9.1 for further discussion).
    NOTE: The limit here is essentially the same minimum as that
    specified for SMTP mail [RFC821].  Implementors are warned that
    Path (see Section 5.6) and References (see Section 6.5) headers,
    in particular, often become several hundred characters long, so
    1000 is not an overly generous limit.
 All implementations MUST be able to handle an article totalling at
 least 65,000 octets, including headers and EOL representations,
 gracefully and efficiently.  All implementations SHOULD be able to
 handle an article totalling at least 1,000,000 (one million) octets,
 including headers and EOL representations, gracefully and
 efficiently.  "Gracefully and efficiently" is intended to preclude
 not only failures, but also major loss of performance, serious
 problems in error recovery, or resource consumption beyond what is
 reasonably necessary.
    NOTE: The intent here is to prohibit lowering the existing de
    facto limit any further, while strongly encouraging movement
    towards a higher one.  Actually, although improvements are
    desirable in some cases, much news software copes reasonably well
    with very large articles.  The same cannot be said of the
    communications software and protocols used to transmit news from
    one host to another, especially when slow communications links are

Spencer Historic [Page 28] RFC 1849 Son of 1036 March 2010

    involved.  Occasional huge articles that appear now (by accident
    or through ignorance) typically leave trails of failing software,
    system problems, and irate administrators in their wake.
    NOTE: It is intended that the successor to this Draft will raise
    the "MUST" limit to 1,000,000 and the "SHOULD" limit still
 Posters SHOULD limit posted articles to at most 60,000 octets,
 including headers and EOL representations, unless the articles are
 being posted only within a cooperating subnet that is known to be
 capable of handling larger articles gracefully.  Posting agents
 presented with a large article SHOULD warn the poster and request
    NOTE: The difference between this and the earlier "MUST" limit is
    due to margin for header growth, differing EOL representations,
    and transmission overheads.
    NOTE: Disagreeable though these limits are, it is a fact that in
    current networks, an article larger than 64K (after header growth,
    etc.) simply is not transmitted reliably.  Note also the comments
    above on the trauma caused by single extremely large articles now;
    the problems are real and current.  These problems arguably should
    be fixed, but this will not happen network-wide in the immediate
    future, hence the restriction of larger articles to cooperating
    subnets, for now.
 Posters using non-ASCII characters in their text MUST take into
 account the overhead involved in MIME encoding, unless the article's
 propagation will be entirely limited to a cooperating subnet that
 does not use MIME encodings for non-ASCII characters.  For example,
 MIME base64 encoding involves growth by a factor of approximately
 4/3, so an article that would likely have to use this encoding should
 be at most about 45,000 octets before encoding.
 Posters SHOULD use MIME "message/partial" conventions to facilitate
 automatic reassembly of a large document split into smaller pieces
 for posting.  It is recommended that the content identifier used
 should be a message ID, generated by the same means as article
 message IDs (see Section 5.3), and that all parts should have a
 See-Also header (see Section 6.16) giving the message IDs of at least
 the previous parts and preferably all of the parts.
    NOTE: See-Also is more correct for this purpose than References,
    although References is in common use today (with less-formal
    reassembly arrangements).  MIME reassemblers should probably

Spencer Historic [Page 29] RFC 1849 Son of 1036 March 2010

    examine articles suggested by References headers if See-Also
    headers are not present to indicate the whereabouts of the other
    parts of "message/partial" articles.
 To repeat: implementations SHOULD avoid fixed constraints on the
 sizes of lines within an article and on the size of the entire

4.7. Example

 Here is a sample article:
    From: jerry@eagle.ATT.COM (Jerry Schwarz)
    Path: cbosgd!mhuxj!mhuxt!eagle!jerry
    Newsgroups: news.announce
    Subject: Usenet Etiquette -- Please Read
    Message-ID: <642@eagle.ATT.COM>
    Date: Mon, 17 Jan 1994 11:14:55 -0500 (EST)
    Followup-To: news.misc
    Expires: Wed, 19 Jan 1994 00:00:00 -0500
    Organization: AT&T Bell Laboratories, Murray Hill

5. Mandatory Headers

 An article MUST have one, and only one, of each of the following
 headers: Date, From, Message-ID, Subject, Newsgroups, Path.
    NOTE: MAIL specifies (if read most carefully) that there must be
    exactly one Date header and exactly one From header, but otherwise
    does not restrict multiple appearances of headers.  (Notably, it
    permits multiple Message-ID headers!)  This appears singularly
    useless, or even harmful, in the context of news, and much current
    news software will not tolerate multiple appearances of mandatory
 Note also that there are situations, discussed in the relevant parts
 of Section 6, where References, Sender, or Approved headers are
 In the discussions of the individual headers, the content of each is
 specified using the syntax notation.  The convention used is that the
 content of, for example, the Subject header is defined as

Spencer Historic [Page 30] RFC 1849 Son of 1036 March 2010

5.1. Date

 The Date header contains the date and time when the article was
 submitted for transmission:
    Date-content  = [ weekday "," space ] date space time
    weekday       = "Mon" / "Tue" / "Wed" / "Thu"
                  / "Fri" / "Sat" / "Sun"
    date          = day space month space year
    day           = 1*2digit
    month         = "Jan" / "Feb" / "Mar" / "Apr" / "May" / "Jun"
                  / "Jul" / "Aug" / "Sep" / "Oct" / "Nov" / "Dec"
    year          = 4digit / 2digit
    time          = hh ":" mm [ ":" ss ] space timezone
    timezone      = "UT" / "GMT"
                  / ( "+" / "-" ) hh mm [ space "(" zone-name ")" ]
    hh            = 2digit
    mm            = 2digit
    ss            = 2digit
    zone-name     = 1*( <ASCII printable character except ()\>
                  / space )
 This is a restricted subset of the MAIL date format.
 If a weekday is given, it MUST be consistent with the date.  The
 modern Gregorian calendar is used, and dates MUST be consistent with
 its usual conventions; for example, if the month is May, the day must
 be between 1 and 31 inclusive.  The year SHOULD be given as four
 digits, and posting agents SHOULD enforce this; however, relayers
 MUST accept the two-digit form, and MUST interpret it as having the
 implicit prefix "19".
    NOTE: Two-digit year numbers can, should, and must be phased out
    by 1999.
 The time is given on the 24-hour clock, e.g., two hours before
 midnight is "22:00" or "22:00:00".  The hh must be between 00 and 23
 inclusive, the mm between 0 and 59 inclusive, and the ss between 0
 and 60 inclusive.
    NOTE: Leap seconds very occasionally result in minutes that are 61
    seconds long.
 The date and time SHOULD be given in the poster's local time zone,
 including a specification of that time zone as a numeric offset
 (which SHOULD include the time zone name, e.g., "EST", supplied in
 parentheses like a MAIL comment).  If not, they MUST be given in
 Universal Time (abbreviated "UT"; "GMT" is a historical synonym for

Spencer Historic [Page 31] RFC 1849 Son of 1036 March 2010

 "UT").  The time zone name in parentheses, if present, is a comment;
 software MUST ignore it, except that reading agents might wish to
 display it to the reader.  Time zone names other than "UT" and "GMT"
 MUST appear only in the comment.
    NOTE: Attempts to deal with a full set of time zone names have all
    foundered on the vast number of such names in use and the
    duplications (for example, there are at least FIVE different time
    zones called "EST" by somebody).  Even the limited set of North
    American zone names authorized by MAIL is subject to confusion and
    misinterpretation, hence the flat ban on non-UT time zone names,
    except as comments.
    NOTE: [RFC1036] specified that use of GMT (aka UT, UTC) was
    preferred.  However, the local time (in the poster's time zone) is
    arguably information of possible interest to the reader, and this
    requires some indication of the poster's time zone.  Numeric
    offsets are an unambiguous way of doing this, and their use was
    indeed sanctioned by [RFC1036] (that is, this is a change of
    preference only).
    NOTE: There is frequent confusion, including errors in some news
    software, regarding the sign of numeric time zones.  Zones west of
    Greenwich have negative offsets.  For example, North American
    Eastern Standard Time is zone -0500 and North American Eastern
    Daylight Time is zone -0400.
    NOTE: Implementors are warned that the hh in a time zone can go up
    to about 14; it is not limited to 12.  This is because the
    International Date Line does not run exactly along the boundary
    between zone -1200 and zone +1200.
    NOTE: The comments in Section 2.6 regarding translation to other
    languages are relevant here.  The Date-content format, and the
    spellings of its components, as found in articles themselves, are
    always as defined in this Draft, regardless of the language used
    to interact with readers and posters.  Reading and posting agents
    should translate as appropriate.  Actually, even English-language
    reading and posting agents will probably want to do some degree of
    translation on dates, if only to abbreviate the lengthy format and
    (perhaps) translate to and from the reader's time zone.

Spencer Historic [Page 32] RFC 1849 Son of 1036 March 2010

5.2. From

 The From header contains the electronic address, and possibly the
 full name, of the article's author:
    From-content  = address [ space "(" paren-phrase ")" ]
                  /  [ plain-phrase space ] "<" address ">"
    paren-phrase  = 1*( paren-char / space / encoded-word )
    paren-char    = <ASCII printable character except ()<>\>
    plain-phrase  = plain-word *( space plain-word )
    plain-word    = unquoted-word / quoted-word / encoded-word
    unquoted-word = 1*unquoted-char
    unquoted-char = <ASCII printable character except !()<>@,;:\".[]>
    quoted-word   = quote 1*( quoted-char / space ) quote
    quote         = <" (ASCII 34)>
    quoted-char   = <ASCII printable character except "()<>\>
    address       = local-part "@" domain
    local-part    = unquoted-word *( "." unquoted-word )
    domain        = unquoted-word *( "." unquoted-word )
 (Encoded words are described in Section 4.5.)  The full name is
 distinguished from the electronic address either by enclosing the
 former in parentheses (making it resemble a MAIL comment, after the
 address) or by enclosing the latter in angle brackets.  The second
 form is preferred.  In the first form, encoded words inside the full
 name MUST be composed entirely of <paren-char>s.  In the second form,
 encoded words inside the full name may not contain characters other
 than letters (of either case), digits, and the characters "!", "*",
 "+", "-", "/", "=", and "_".  The local part is case-sensitive
 (except that all case counterparts of "postmaster" are deemed
 equivalent), the domain is case-insensitive, and all other parts of
 the From content are comments that MUST be ignored by news software
 (except insofar as reading agents may wish to display them to the
 reader).  Posters and posting agents MUST restrict themselves to this
 subset of the MAIL From syntax; relayers MAY accept a broader subset,
 but see the discussion in Section 9.1.
    NOTE: The syntax here is a restricted subset of the MAIL From
    syntax, with quoting particularly restricted, for simple parsing.
    In particular, the presence of "<" in the From content indicates
    that the second form is being used; otherwise, the first form is
    being used.  The major restrictions here are those already de
    facto imposed by existing software.
    NOTE: Overly lenient posting agents sometimes permit the second
    form with a full name containing "(" or ")", but it is extremely
    rare for a full name to contain "<" or ">", even in mail.

Spencer Historic [Page 33] RFC 1849 Son of 1036 March 2010

    Accordingly, reading agents wishing to robustly determine which
    form is in use in a particular article should key on the presence
    or absence of "<", not the presence or absence of "(".
 The address SHOULD be a valid and complete Internet domain address,
 capable of being successfully mailed to by an Internet host (possibly
 via an MX (Mail Exchange) record and a forwarder).  The pseudo-domain
 ".uucp" MAY be used for hosts registered in the UUCP maps (e.g., name
 "xyz.uucp" for registered site "xyz"), but such hosts SHOULD
 discontinue this usage (either by arranging a proper Internet address
 and forwarder, or by using the "% hack" (see below)), as soon as
 possible.  Bitnet hosts SHOULD use Internet addresses, avoiding the
 obsolescent ".bitnet" pseudo-domain.  Other forms of address MUST NOT
 be used.
    NOTE: "Other forms" specifically include UK-style "backward"
    domains ("uk.oxbridge.cs" is in the Czech Republic, not the UK),
    pure-UUCP addressing ("knee!shin!foot" instead of
    "foot%shin@knee.uucp"), and abbreviated domains ("zebra.zoo"
    instead of "").
 If it is necessary to use the local part to specify a routing
 relative to the nearest Internet host, this MUST be done using the "%
 hack", using "%" as a secondary "@".  For example, to specify that
 mail to the address should go to Internet host "", then to
 non-Internet host "ein", then to non-Internet host "deux", for
 delivery there to mailbox "fred", a suitable address would be:
 Analogous forms using "!" in the local part MUST NOT be used, as they
 are ambiguous; they should be expressed in the "%" form.
    NOTE: "a!b@c" can be interpreted as either "b%c@a" or "b%a@c", and
    there is no consistency in which choice is made.  Such addresses
    consequently are unreliable.  The "%" form does not suffer from
    this problem, and although its use is officially discouraged, it
    is a de facto standard, to the point that MAIL recognizes it.
 Relayers MUST NOT, repeat MUST NOT, repeat MUST NOT, rewrite From
 lines, in any way, however minor or seemingly innocent.  Trying to
 "fix" a non-conforming address has a very high probability of making
 things worse.  Either pass it along unchanged or reject the article.
    NOTE: An additional reason for banning the use of "!"  addressing
    is that it has a much higher probability of being rewritten into
    mangled unrecognizability by old relayers.

Spencer Historic [Page 34] RFC 1849 Son of 1036 March 2010

 Posters and posting agents SHOULD avoid use of the characters "!" and
 "@" in full names, as they may trigger unwanted header rewriting by
 old, simple-minded news software.
    NOTE: Also, the characters "." and ",", not infrequently found in
    names (e.g., "John W. Campbell, Jr."), are NOT, repeat NOT,
    allowed in an unquoted word.  A From header like the following
    MUST NOT be written without the quotation marks:
    From: "John W. Campbell, Jr." <>

5.3. Message-ID

 The Message-ID header contains the article's message ID, a unique
 identifier distinguishing the article from every other article:
    Message-ID-content  = message-id
    message-id          = "<" local-part "@" domain ">"
 As with From addresses, a message ID's local part is case-sensitive,
 and its domain is case-insensitive.  The "<" and ">" are parts of the
 message ID, not peculiarities of the Message-ID header.
    NOTE: News message IDs are a restricted subset of MAIL message
    IDs.  In particular, no existing news software copes properly with
    MAIL quoting conventions within the local part, so they are
    forbidden.  This is unfortunate, particularly for X.400 gateways
    that often wish to include characters that are not legal in
    unquoted message IDs, but it is impossible to fix net-wide.  See
    the notes on gatewaying in Section 10.
 The domain in the message ID SHOULD be the full Internet domain name
 of the posting agent's host.  Use of the ".uucp" pseudo-domain (for
 hosts registered in the UUCP maps) or the ".bitnet" pseudo-domain
 (for Bitnet hosts) is permissible but SHOULD be avoided.
 Posters and posting agents MUST generate the local part of a message
 ID using an algorithm that obeys the specified syntax (words
 separated by ".", with certain characters not permitted) (see Section
 5.2 for details) and will not repeat itself (ever).  The algorithm
 SHOULD NOT generate message IDs that differ only in case of letters.
 Note the specification in Section 6.5 of a recommended convention for
 indicating subject changes.  Otherwise, the algorithm is up to the
    NOTE: The crucial use of message IDs is to distinguish circulating
    articles from each other and from articles circulated recently.
    They are also potentially useful as permanent indexing keys, hence

Spencer Historic [Page 35] RFC 1849 Son of 1036 March 2010

    the requirement for permanent uniqueness, but indexers cannot
    absolutely rely on this because the earlier RFCs urged it but did
    not demand it.  All major implementations have always generated
    permanently unique message IDs by design, but in some cases this
    is sensitive to proper administration, and duplicates may have
    occurred by accident.
    NOTE: The most popular method of generating local parts is to use
    the date and time, plus some way of distinguishing between
    simultaneous postings on the same host (e.g., a process number),
    and encode them in a suitably restricted alphabet.  An older but
    now less-popular alternative is to use a sequence number,
    incremented each time the host generates a new message ID; this is
    workable but requires careful design to cope properly with
    simultaneous posting attempts, and it is not as robust in the
    presence of crashes and other malfunctions.
    NOTE: Some buggy news software considers message IDs completely
    case-insensitive, hence the advice to avoid relying on case
    distinctions.  The restrictions placed on the "alphabet" of local
    parts and domains in Section 5.2 have the useful side effect of
    making it unnecessary to parse message IDs in complex ways to
    break them into case-sensitive and case-insensitive portions.
 The local part of a message ID MUST NOT be "postmaster" or any other
 string that would compare equal to "postmaster" in a case-insensitive
 comparison.  Message IDs MUST be no longer than 250 octets, including
 the "<" and ">".
    NOTE: "Postmaster" is an irksome exception to case-sensitivity in
    local parts, inherited from MAIL, and simply avoiding it is the
    best way to deal with it (not that it's likely, but the issue
    needs to be dealt with).  The length limit is undesirable but is
    present in widely used existing software.  The limit is actually
    255, but a small safety margin is wise.

5.4. Subject

 The Subject header's content (the "subject" of the article) is a
 short phrase describing the topic of the article:
    Subject-content  = [ "Re: " ] nonblank-text
 Encoded words MAY appear in this header.

Spencer Historic [Page 36] RFC 1849 Son of 1036 March 2010

 If the article is a followup, the subject SHOULD begin with "Re: " (a
 "back reference").  If the article is not a followup, the subject
 MUST NOT begin with a back reference.  Back references are case-
 insensitive, although "Re: " is the preferred form.  A followup agent
 assisting a poster in preparing a followup SHOULD prepend a back
 reference, UNLESS the subject already begins with one.  If the poster
 determines that the topic of the followup differs significantly from
 what is described in the subject, a new, more descriptive subject
 SHOULD be substituted (with no back reference).  An article whose
 subject begins with a back reference MUST have a References header
 referencing the precursor.
    NOTE: A back reference is FOUR characters, the fourth being a
    blank. [RFC1036] was confused about this.  Observe also that only
    ONE back reference should be present.
    NOTE: There is a semi-standard convention, often used, in which a
    subject change is flagged by making the new Subject-content of the
    new topic (was: old topic)
    possibly with "old topic" somewhat truncated.  Posters wishing to
    do something like this are urged to use this exact form, to
    simplify automated analysis.
 For historical reasons, the subject MUST NOT begin with "cmsg " (note
 that this sequence ends with a blank).
    NOTE: Some old news software takes a subject beginning with
    "cmsg " as an indication that the article is a control message
    (see Sections 6.6 and 7).  This mechanism is obsolete and
    undesirable, but accidental triggering of it is still possible.
 The subject SHOULD be terse.  Posters SHOULD avoid trying to cram
 their entire article into the headers; even the simplest query
 usually benefits from a sentence or two of elaboration and context,
 and the details of header display vary widely among reading agents.
    NOTE: All-in-the-subject articles are sometimes the result of
    misunderstandings over the interaction protocol of a posting
    agent.  Posting agents might wish to give special attention to the
    possibility that a poster specifying a very long subject might
    have thought he was typing the body of the article.

Spencer Historic [Page 37] RFC 1849 Son of 1036 March 2010

5.5. Newsgroups

 The Newsgroups header's content specifies to which newsgroup(s) the
 article is posted:
    Newsgroups-content  = newsgroup-name *( ng-delim newsgroup-name )
    newsgroup-name      = plain-component *( "." component )
    component           = plain-component / encoded-word
    plain-component     = component-start *13component-rest
    component-start     = lowercase / digit
    lowercase           = <letter a-z>
    component-rest      = component-start / "+" / "-" / "_"
    ng-delim            = ","
 Encoded words used in newsgroup names MUST NOT contain characters
 other than letters, digits, "+", "-", "/", "_", "=", and "?"
 (although they may encode them).
 A newsgroup name consists of one or more components, which may be
 plain components or (except for the first) encoded words.  A plain
 component MUST contain at least one letter, MUST begin with a letter
 or digit, and MUST NOT be longer than 14 characters.  The first
 component MUST begin with a letter; subsequent components SHOULD
 begin with a letter.  Newsgroup names MUST NOT contain uppercase
 letters, except where required by encodings in encoded words.  The
 sequences "all" and "ctl" MUST NOT be used as components.
    NOTE: The alphabet and syntax specified encompasses all existing
    names of widespread newsgroups, while avoiding various forms that
    are known to cause problems.  Important existing software uses
    various non-alphanumeric characters as punctuation adjacent to
    newsgroup names.  (It would, in fact, be preferable to ban "+"
    from newsgroup names, were it not that several widespread
    newsgroups related to the C++ programming language already use
    NOTE: Much existing software converts the newsgroup name into a
    directory path and stores the articles themselves using numeric
    filenames, so all-digit name components can be troublesome; the
    "Great Renaming" early in the history of Usenet included revisions
    of several newsgroup names to eliminate such components.
    NOTE: The same storage technique is the reason for the
    14-character limit.  The limit is now largely historical, since
    most modern systems have much larger limits on the length of a
    directory entry's name, but many old systems are still in use.
    Systems with shorter limits also exist, but news software on such
    systems has had to deal with the problem already, since there are

Spencer Historic [Page 38] RFC 1849 Son of 1036 March 2010

    several widespread newsgroups with 14-character components in
    their names.  Implementors are warned that it is intended that the
    successor to this Draft will increase the 14-character limit, and
    they are urged to fix their software to handle longer names
    gracefully (if such fixes are necessary, given the intended domain
    of application of the particular software).
    NOTE: The requirement that the first character of a name be a
    letter accommodates existing software that assumes it can tell the
    difference between a newsgroup name and other possible syntactic
    entities by inspecting the first character.  Similar
    considerations motivate excluding "+", "-", and "_" from coming
    first in a component, and the preference for components that do
    not begin with digits.  The "all" sequence is used as a wildcard
    symbol in much existing software, and the "ctl" sequence was
    involved in an obsolete historical mechanism for marking control
    messages, so they are best avoided.
    NOTE: Possibly newsgroup names should have been case-insensitive,
    but all existing software treats them as case-sensitive.
    ([RFC977] claims that they are case-insensitive in NNTP, but
    existing implementations are believed to ignore this.)  The
    simplest solution is just to ban use of uppercase letters, since
    no widespread newsgroup name uses them anyway; this avoids any
    possibility of confusion.
    NOTE: The syntax has the disadvantage of containing no white
    space, making it impossible to continue a Newsgroups header across
    several lines.  Implementors of relayers and reading agents are
    warned that it is intended that the successor to this Draft will
    change the definition of ng-delim to:
    ng-delim = "," [ space ]
    and are urged to fix their software to handle (i.e., ignore) white
    space following the commas.  Meanwhile, posters must avoid
    inserting such space (despite the natural-language convention that
    permits it), and posting agents should strip it out.
    NOTE: Encoded words as components are somewhat problematic but are
    clearly desirable for use in non-English-speaking nations.  They
    are not subject to the 14-character limit, and this (plus the
    possibility of "/" within them) may require special handling in
    news software.

Spencer Historic [Page 39] RFC 1849 Son of 1036 March 2010

 Encoded words are allowed in newsgroup names ONLY where non-ASCII
 characters are necessary to the name, and they must use the "b"
 encoding [RFC2045] and the first suitable character set in the MIME
 order of preferred character sets [RFC2047] {ASCII before ISO-8859-*
 before anything else}.
    NOTE: Since the newsgroup name is the encoded form, NOT the
    underlying non-ASCII form, there is room for terrible confusion
    here if the choice of encoding for a particular name is not fully
 Posters SHOULD use only the names of existing newsgroups in the
 Newsgroups header, because newsgroups are NOT created simply by being
 posted to.  However, it is legitimate to cross-post to newsgroup(s)
 that do not exist on the posting agent's host, provided that at least
 one of the newsgroups DOES exist there, and followup agents MUST
 accept this (posting agents MAY accept it, but SHOULD at least alert
 the poster to the situation and request confirmation).  Relayers MUST
 NOT rewrite Newsgroups headers in any way, even if some or all of the
 newsgroups do not exist on the relayer's host.
    NOTE: Early experience with news software that created newsgroups
    when they were mentioned in a Newsgroups header was thoroughly
    negative: posters frequently mistype newsgroup names.
    NOTE: While it is legitimate for some of an article's newsgroups
    not to exist on the host where it is posted, this IS a rather
    unusual situation except in followups (which should go to all
    newsgroups the precursor was posted to, even if not all of them
    reach the site where the followup is being posted).
    NOTE: Rewriting Newsgroups headers to strip locally unknown
    newsgroups is superficially attractive.  However, early experience
    with exactly that policy was thoroughly negative: news propagation
    is more redundant and much less orderly than many people imagine,
    and in particular it is not unheard of for the (sometimes) fastest
    path between two (say) University of Toronto sites to pass outside
    the University of Toronto, in which case newsgroup stripping can
    cause incomplete propagation.  Having an article's set of
    newsgroups change as it propagates can also result in followups
    not achieving the same propagation as the original.  It's been
    tried; it's more trouble than it's worth; don't do it.
    NOTE: In particular, newsgroup stripping superficially looks like
    a solution to the problem of duplicate regional newsgroup names.
    For example, both the University of Toronto and the University of
    Texas have "ut.general" newsgroups, and material cross-posted to
    that name and a global newsgroup appears in both universities'

Spencer Historic [Page 40] RFC 1849 Son of 1036 March 2010

    local newsgroups.  However, the side effects of stripping are
    sufficiently unacceptable to disqualify it for this purpose.
    Don't do it.
 Cross-posting an article to several relevant newsgroups is far
 superior to posting separate articles with duplicated content to each
 newsgroup, because reading agents can detect the situation and show
 the article to a reader only once.  Posters SHOULD cross-post rather
 than duplicate-post.
    NOTE: On the other hand, cross-posting to a large number of
    newsgroups usually indicates that the poster has not thought about
    his audience; articles are rarely pertinent to more than (say)
    half a dozen newsgroups.  Posting agents might wish to request
    confirmation when the number of newsgroups exceeds (say) five in
    the presence of a Followup-To header, or (say) two in the absence
    of such a header.
    NOTE: One problem with cross-postings is what to do with an
    article cross-posted to a set of newsgroups including both
    moderated and unmoderated ones.  Posters tend to expect such an
    article to show up immediately in the unmoderated newsgroups,
    especially if they do not realize that one or more of the
    newsgroups is moderated.  However, since it is not possible for a
    moderator to retroactively add an already-posted article to a
    moderated newsgroup, the only correct action is to mail such an
    article to one (and only one) of the moderators for action.  It is
    probably best for the posting agent to detect this situation and
    ask the poster what action is preferred.  The acceptable choices
    are to alter the newsgroup list or to mail to a moderator of the
    poster's choice; the posting agent should NOT offer duplicate-
    posting as an easy-to-request option (if only because many
    moderators will reject a submission that has already been posted
    to unmoderated newsgroups).
    NOTE: An article cross-posted to multiple moderated newsgroups
    really should have approval from all of the moderators involved.
    In practice, the only straightforward way to do this is to send
    the article to one of them and have him consult the others.
 A newsgroup SHOULD NOT appear more than once in the Newsgroups
 Newsgroup names having only one component are reserved for newsgroups
 whose propagation is restricted to a single host (or the
 administrative equivalent).  It is inadvisable to name a newsgroup

Spencer Historic [Page 41] RFC 1849 Son of 1036 March 2010

 "poster" because that word has special meaning in the Followup-To
 header (see Section 6.1).  The names "control" and "junk" are
 frequently used for pseudo-newsgroups internal to relayer
 implementations, and hence are also best avoided.
    NOTE: Beware of the duplicate-regional-newsgroup-names problem
    mentioned above.  In particular, there are many, many hosts with a
    newsgroup named "general", and some surprising things show up in
    such newsgroups when people cross-post.  It is probably better to
    use multi-component names, which are less likely to be duplicated.
    Fred's Widget House should use "fwh.general" rather than just
    "general" as its in-house general-topics newsgroup.
 It is conventional to reserve newsgroup names beginning with "to."
 for test messages sent on an essentially point-to-point basis (see
 also the ihave/sendme protocol described in Section 7.2); newsgroup
 names beginning with "to." SHOULD NOT be used for any other purpose.
 The second (and possibly later) components of such a name should,
 together, comprise the relayer name (see Section 5.6) of a relayer.
 The newsgroup exists only at the named relayer and its neighbors.
 The neighbors all pass that newsgroup to the named relayer, while the
 named relayer does not pass it to anyone.
 The order of newsgroup names in the Newsgroups header is not

5.6. Path

 The Path header's content indicates which relayers the article has
 already visited, so that unnecessary redundant transmission can be
    Path-content    = [ path-list path-delimiter ] local-part
    path-list       = relayer-name *( path-delimiter relayer-name )
    relayer-name    = 1*rn-char
    rn-char         = letter / digit / "." / "-" / "_"
    path-delimiter  = "!"
 The Path content is a list of relayer names, separated by path
 delimiters, followed (after a final delimiter) by the local part of a
 mailing address.  Each relayer MUST prepend its name, and a
 delimiter, to the Path content in all articles it processes.  A
 relayer MUST NOT pass an article to a neighboring relayer whose name
 is already mentioned in an article's path list, unless this is
 explicitly requested by the neighbor in some way.  The Path content
 is case-sensitive.

Spencer Historic [Page 42] RFC 1849 Son of 1036 March 2010

    NOTE: The Path header supplied by a posting agent should normally
    contain only the local part.  The relayer that the posting agent
    passes the article to for posting will prepend its relayer name to
    get the path list started.
    NOTE: Observe that the trailing local part is NOT part of the path
    list.  This Path header:
       Path: fee!fie!foe!fum
    contains three relayer names: "fee", "fie", and "foe".  A relayer
    named "fum" is still eligible to be sent this article.
    NOTE: This syntax has the disadvantage of containing no white
    space, making it impossible to continue a Path header across
    several lines.  Implementors of relayers and reading agents are
    warned that it is intended that the successor to this Draft will
    change the definition of path delimiter to:
       path-delimiter = "!" [ space ]
    and are urged to fix their software to handle (i.e., ignore) white
    space following the exclamation points.  They are urged to hurry;
    some ill-behaved systems reportedly already feel free to add such
    white space.
    NOTE: [RFC1036] allows considerably more flexibility in choice of
    delimiter, in theory, but this flexibility has never been used,
    and most news software does not implement it properly.  The
    grammar reflects the current reality.  Note, in particular, that
    [RFC1036] treats "_" as a delimiter, but in fact it is known to
    appear in relayer names occasionally.
 Because an article will not propagate to a relayer already mentioned
 in its path list, the path list MUST NOT contain any names other than
 those of relayers the article has passed through AS NEWS.  This is
 trivially obvious for normal news articles but requires attention
 from the moderators of moderated newsgroups and the implementors and
 maintainers of gateways.
    NOTE: For the same reason, a relayer and its neighbors need to
    agree on the choice of relayer name, and names should not be
    changed without notifying neighbors.
 Relayer names need to be unique among all relayers that will ever see
 the articles using them.  A relayer name is normally either an
 "official" name for the host the relayer runs on, or some other
 "official" name controlled by the same organization.  Except in

Spencer Historic [Page 43] RFC 1849 Son of 1036 March 2010

 cooperating subnets that agree to some other convention and don't let
 articles using it escape beyond the subnet, a relayer name MUST be
 either a UUCP name registered in the UUCP maps (without any domain
 suffix such as ".UUCP") or a complete Internet domain name.  Use of a
 (registered) UUCP name is recommended, where practical, to keep the
 length of the path list down.
 The use of Internet domain names in the path list presents one
 problem: domain names are case-insensitive, but the path list is
 case-sensitive.  Relayers using domain names as their relayer names
 MUST pick a standard form for the name and use that form consistently
 to the exclusion of all others.  The preferred form for this purpose,
 which relayers SHOULD use, is the all-lowercase form.
    NOTE: It is arguably unfortunate that the path list is case-
    sensitive, but it is much too late to change this.  Most Internet
    sites do, in any event, use one standardized form of their name
    almost everywhere.
 In the ordinary case, where the poster is the author of the article,
 the local part following the path list SHOULD be the local part of
 the poster's full Internet domain mailing address.
    NOTE: It should be just the local part, not the full address.  The
    character "@" does not appear in a Path header.
 The Path content somewhat resembles a mailing address, particularly
 in the UUCP world with its manual routing and "!" address syntax.
 Historically, this resemblance was important, and the Path content
 was often used as a reply address.  This practice has always been
 somewhat unreliable, since news paths are not always mail paths and
 news relayer names are not always recognized by mail handlers, and
 its reliability has generally worsened in recent times.  The
 widespread use of and recognition of Internet domain addresses, even
 outside the actual Internet, has largely eliminated the problem.
 Readers SHOULD NOT use the Path content as a reply address.  On the
 other hand, relayer administrators are urged not to break this usage
 without good reason; where practical, paths followed by news SHOULD
 be traversable by mail, and mail handlers SHOULD recognize relayer
 names as host names.
 It will typically be difficult or impractical for gateways and
 moderators to supply a Path content that is useful as a reply address
 for the author, bearing in mind that the path list they supply will
 normally be empty.  (To reiterate: the path list MUST NOT contain any
 names other than those of relayers the article has passed through AS
 NEWS.)  They SHOULD supply a local part that will result in replies

Spencer Historic [Page 44] RFC 1849 Son of 1036 March 2010

 to a Path-derived address being returned to the sender with a brief
 explanation.  Software permitting, the local part "not-for-mail" is
    NOTE: A moderator or gateway administrator who supplies a local
    part that delivers such mail to an administrative mailbox will
    quickly discover why it should be bounced automatically!  It is
    best, however, for the returned message to include an explanation
    of what has probably happened, rather than just a mysterious
    "undeliverable mail" complaint, since the sender may not be aware
    that his/her software is unwisely using the Path content as a
    reply address.  Reply software might wish to question attempts to
    reply to a Path-derived address ending in "not-for-mail" (which is
    why a specific name is being recommended here).

6. Optional Headers

 Many MAIL headers, and many of those specified in present and future
 MAIL extensions, are potentially applicable to news.  Headers
 specific to MAIL's point-to-point transmission paradigm, e.g., To and
 Cc, SHOULD NOT appear in news articles.  (Gateways wishing to
 preserve such information for debugging probably SHOULD hide it under
 different names; prefixing "X-" to the original headers, resulting in
 forms like "X-To", is suggested.)
 The following optional headers are either specific to news or of
 particular note in news articles; an article MAY contain some or all
 of them.  (Note that there are some circumstances in which some of
 them are mandatory; these are explained under the individual
 headers.)  An article MUST NOT contain two or more headers with any
 one of these header names.
    NOTE: The ban on duplicate header names does not apply to headers
    not specified in this Draft, such as "X-" headers.  Software
    should not assume that all header names in a given article are

6.1. Followup-To

 The Followup-To header contents specify to which newsgroup(s)
 followups should be posted:
    Followup-To-content = Newsgroups-content / "poster"

Spencer Historic [Page 45] RFC 1849 Son of 1036 March 2010

 The syntax is the same as that of the Newsgroups content, with the
 exception that the magic word "poster" means that followups should be
 mailed to the article's reply address rather than posted.  In the
 absence of Followup-To, the default newsgroup(s) for a followup are
 those in the Newsgroups header.
    NOTE: The way to request that followups be mailed to a specific
    address other than that in the From line is to supply
    "Followup-To: poster" and a Reply-To header.  Putting a mailing
    address in the Followup-To line is incorrect; posting agents
    should reject or rewrite such headers.
    NOTE: There is no syntax for "no followups allowed" because
    "Followup-To: poster" accomplishes this effect without extra
 Although it is generally desirable to limit followups to the smallest
 reasonable set of newsgroups, especially when the precursor was
 cross-posted widely, posting agents SHOULD NOT supply a Followup-To
 header except at the poster's explicit request.
    NOTE: In particular, it is incorrect for the posting agent to
    assume that followups to a cross-posted article should be directed
    to the first newsgroup only.  Trimming the list of newsgroups
    should be the poster's decision, not the posting agent's.
    However, when an article is to be cross-posted to a considerable
    number of newsgroups, a posting agent might wish to SUGGEST to the
    poster that followups go to a shorter list.

6.2. Expires

 The Expires header content specifies a date and time when the article
 is deemed to be no longer useful and should be removed ("expired"):
    Expires-content = Date-content
 The content syntax is the same as that of the Date content.  In the
 absence of Expires, the default is decided by the administrators of
 each host the article reaches, who MAY also restrict the extent to
 which the Expires header is honored.
 The Expires header has two main applications: removing articles whose
 utility ends on a specific date (e.g., event announcements that can
 be removed once the day of the event has passed) and preserving
 articles expected to be of prolonged usefulness (e.g., information
 aimed at new readers of a newsgroup).  The latter application is
 sometimes abused.  Since individual hosts have local policies for
 expiration of news (depending on available disk space, for instance),

Spencer Historic [Page 46] RFC 1849 Son of 1036 March 2010

 posters SHOULD NOT provide Expires headers for articles unless there
 is a natural expiration date associated with the topic.  Posting
 agents MUST NOT provide a default Expires header.  Leave it out and
 allow local policies to be used unless there is a good reason not to.
 Expiry dates are properly the decision of individual host
 administrators; posters and moderators SHOULD set only expiry dates
 with which most administrators would agree.
    NOTE: A poster preparing an Expires header for an article whose
    utility ends on a specific day should typically specify the NEXT
    day as the expiry date.  A meeting on July 7th remains of interest
    on the 7th.

6.3. Reply-To

 The Reply-To header content specifies a reply address different from
 the author's address given in the From header:
    Reply-To-content = From-content
 In the absence of Reply-To, the reply address is the address in the
 From header.
 Use of a Reply-To header is preferable to including a similar request
 in the article body, because reply-preparation software can take
 account of Reply-To automatically.

6.4. Sender

 The Sender header identifies the poster, in the event that this
 differs from the author identified in the From header:
    Sender-content = From-content
 In the absence of Sender, the default poster is the author (named in
 the From header).
    NOTE: The intent is that the Sender header have a fairly high
    probability of identifying the person who really posted the
    article.  The ability to specify a From header naming someone
    other than the poster is useful but can be abused.
 If the poster supplies a From header, the posting agent MUST ensure
 that a Sender header is present, unless it can verify that the
 mailing address in the From header is a valid mailing address for the
 poster.  A poster-supplied Sender header MAY be used, if its mailing
 address is verifiably a valid mailing address for the poster;

Spencer Historic [Page 47] RFC 1849 Son of 1036 March 2010

 otherwise, the posting agent MUST supply a Sender header and delete
 (or rename, for example, to X-Unverifiable-Sender) any poster-
 supplied Sender header.
    NOTE: It might be useful to preserve a poster-supplied Sender
    header so that the poster can supply the full-name part of the
    content.  The mailing address, however, must be right, hence, the
    posting agent must generate the Sender header if it is unable to
    verify the mailing address of a poster-supplied one.
    NOTE: NNTP implementors, in particular, are urged to note this
    requirement (which would eliminate the need for ad hoc headers
    like NNTP-Posting-Host), although there are admittedly some
    implementation difficulties.  A user name from an [RFC1413] server
    and a host name from an inverse mapping of the address, perhaps
    with a "full name" comment noting the origin of the information,
    would be at least a first approximation:
    Sender: (RFC-1413@reverse-lookup;
                                  not verified)
 While this does not completely meet the specs, it comes a lot closer
 than not having a Sender header at all.  Even just supplying a
 placeholder for the user name:
    Sender: (user name unknown)
 would be better than nothing.

6.5. References

 The References header content lists message IDs of precursors:
    References-content = message-id *( space message-id )
 A followup MUST have a References header, and an article that is not
 a followup MUST NOT have a References header.  The References-content
 of a followup MUST be the precursor's References-content (if any)
 followed by the precursor's message ID.
    NOTE: Use the See-Also header (Section 6.16) for interconnection
    of articles that are not in a followup relationship to each other.
    NOTE: In retrospect, RFCs 850 and 1036, and the implementations
    whose practice they represented, erred here.  The proper MAIL
    header to use for references to precursors is In-Reply-To, and the
    References header is meant to be used for the purposes here
    ascribed to See-Also.  This incompatibility is far too solidly

Spencer Historic [Page 48] RFC 1849 Son of 1036 March 2010

    established to be fixed, unfortunately.  The best that can be done
    is to provide a clear mapping between the two and urge gateways to
    do the transformation.  The news usage is (now) a deliberate
    violation of the MAIL specifications; articles containing news
    References headers are technically not valid MAIL messages,
    although it is unlikely that much MAIL software will notice
    because the incompatibility is at a subtle semantic level that
    does not affect the syntax.
    UNRESOLVED ISSUE: Would it be better to just give up and admit
    that news uses References for both purposes?
    UNRESOLVED ISSUE: Should the syntax be generalized to include URLs
    as alternatives to message IDs?  Perhaps not; too many things know
    about References already.  And non-articles can't be precursors of
    articles, not really.
 Followup agents SHOULD NOT shorten References headers.  If it is
 absolutely necessary to shorten the header, as a desperate last
 resort, a followup agent MAY do this by deleting some of the message
 IDs.  However, it MUST NOT delete the first message ID, the last
 three message IDs (including that of the immediate precursor), or any
 message ID mentioned in the body of the followup.  If it is possible
 for the followup agent to determine the Subject content of the
 articles identified in the References header, it MUST NOT delete the
 message ID of any article where the Subject content changed (other
 than by prepending of a back reference).  The followup agent MUST NOT
 delete any message ID whose local part ends with "_-_" (underscore
 (ASCII 95), hyphen (ASCII 45), underscore); followup agents are urged
 to use this form to mark subject changes and to avoid using it
    NOTE: As software capable of exploiting References chains has
    grown more common, the random shortening permitted by [RFC1036]
    has become increasingly troublesome.  ANY shortening is
    undesirable, and software should do it only in cases of dire
    necessity.  In such cases, these rules attempt to limit the
    NOTE: The first message ID is very important as the starting point
    of the "thread" of discussion and absolutely should not be
    deleted.  Keeping the last three message IDs gives thread-
    following software a fighting chance to reconstruct a full thread
    even if an article or two is missing.  Keeping message IDs
    mentioned in the body is obviously desirable.

Spencer Historic [Page 49] RFC 1849 Son of 1036 March 2010

    NOTE: Subject changes are difficult to determine, but they are
    significant as possible beginnings of new threads.  The "_-_"
    convention is provided so that posting agents (which have more
    information about subjects) can flag articles containing a subject
    change in a way that followup agents can detect without access to
    the articles themselves.  The sequence is chosen as one that is
    fairly unlikely to occur by accident.
    UNRESOLVED ISSUE: Is "_-_" really worth having?
 When a References header is shortened, at least three blanks SHOULD
 be left between adjacent message IDs at each point where deletions
 were made.  Software preparing new References headers SHOULD preserve
 multiple blanks in older References content.
    NOTE: It's desirable to have some marker of where deletions
    occurred, but the restricted syntax of the header makes this
    difficult.  Extra white space is not a very good marker, since it
    may be deleted by software that ill-advisedly rewrites headers,
    but at least it doesn't break existing software.
 To repeat: followup agents SHOULD NOT shorten References headers.
    NOTE: Unfortunately, reading agents and other software analyzing
    References patterns have to be prepared for the worst anyway.  The
    worst includes random deletions and the possibility of circular
    References chains (when References is misused in place of See-Also
    (Section 6.16)).

6.6. Control

 The Control header content marks the article as a control message and
 specifies the desired actions (other than the usual ones of filing
 and passing on the article):
    Control-content  = verb *( space argument )
    verb             = 1*( letter / digit )
    argument         = 1*<ASCII printable character>
 The verb indicates what action should be taken, and the argument(s)
 (if any) supply details.  In some cases, the body of the article may
 also contain details.  Section 7 describes the standard verbs.  See
 also the Also-Control header (Section 6.15).
    NOTE: Control messages are often processed and filed rather
    differently than normal articles.

Spencer Historic [Page 50] RFC 1849 Son of 1036 March 2010

    NOTE: The restriction of verbs to letters and digits is new but is
    consistent with existing practice and potentially simplifies
    implementation by avoiding characters significant to command
    interpreters.  Beware that the arguments are under no such
    restriction in general.
    NOTE: Two other conventions for distinguishing control messages
    from normal articles were formerly in use: a three-component
    newsgroup name ending in ".ctl" or a subject beginning with
    "cmsg " was considered to imply that the article was a control
    message.  These conventions are obsolete.  Do not use them.
 An article with a Control header MUST NOT have an Also-Control or
 Supersedes header.

6.7. Distribution

 The Distribution header content specifies geographic or
 organizational limits on an article's propagation:
    Distribution-content  = distribution *( dist-delim distribution )
    dist-delim            = ","
    distribution          = plain-component
 A distribution is syntactically identical to a one-component
 newsgroup name and must satisfy the same rules and restrictions.  In
 the absence of Distribution, the default distribution is "world".
    NOTE: This syntax has the disadvantage of containing no white
    space, making it impossible to continue a Distribution header
    across several lines.  Implementors of relayers and reading agents
    are warned that it is intended that the successor to this Draft
    will change the definition of dist delimiter to:
       dist-delim = "," [ space ]
    and are urged to fix their software to handle (i.e., ignore) white
    space following the commas.
 A relayer MUST NOT pass an article to another relayer unless
 configuration information specifies transmission to that other
 relayer of BOTH (a) at least one of the article's newsgroup(s), and
 (b) at least one of the article's distribution(s).  In effect, the
 only role of distributions is to limit propagation, by preventing
 transmission of articles that would have been transmitted had the
 decision been based solely on newsgroups.

Spencer Historic [Page 51] RFC 1849 Son of 1036 March 2010

 A posting agent might wish to present a menu of possible
 distributions, or suggest a default, but normally SHOULD NOT supply a
 default without giving the poster a chance to override it.  A
 followup agent SHOULD initially supply the same Distribution header
 as found in the precursor, although the poster MAY alter this if
 Despite the syntactic similarity and some historical confusion,
 distributions are NOT newsgroup names.  The whole point of putting a
 distribution on an article is that it is DIFFERENT from the
 newsgroup(s).  In general, a meaningful distribution corresponds to
 some sort of region of propagation: a geographical area, an
 organization, or a cooperating subnet.
    NOTE: Distributions have historically suffered from the completely
    uncontrolled nature of their name space, the lack of feedback to
    posters on incomplete propagation resulting from use of random
    trash in Distribution headers, and confusion with newsgroups
    (arising partly because many regions and organizations DO have
    internal newsgroups with names resembling their internal
    distributions).  This has resulted in much garbage in Distribution
    headers, notably the pointless practice of automatically supplying
    the first component of the newsgroup name as a distribution (which
    is MOST unlikely to restrict propagation!).  Many sites have opted
    to maximize propagation of such ill-formed articles by essentially
    ignoring distributions.  This unfortunately interferes with
    legitimate uses.  The situation is bad enough that distributions
    must be considered largely useless except within cooperating
    subnets that make an organized effort to restrain propagation of
    their internal distributions.
    NOTE: The distributions "world" and "local" have no standard magic
    meaning (except that the former is the default distribution if
    none is given).  Some pieces of software do assign such meanings
    to them.

6.8. Keywords

 The Keywords header content is one or more phrases intended to
 describe some aspect of the content of the article:
    Keywords-content = plain-phrase *( "," [ space ] plain-phrase )
 Keywords, separated by commas, each follow the <plain-phrase> syntax
 defined in Section 5.2.  Encoded words in keywords MUST NOT contain
 characters other than letters (of either case), digits, and the
 characters "!", "*", "+", "-", "/", "=", and "_".

Spencer Historic [Page 52] RFC 1849 Son of 1036 March 2010

    NOTE: Posters and posting agents are asked to take note that
    keywords are separated by commas, not by white space.  The
    following Keywords header contains only one keyword (a rather
    unlikely and improbable one):
    Keywords: Thompson Ritchie Multics Linux
    and should probably have been written:
    Keywords: Thompson, Ritchie, Multics, Linux
    This particular error is unfortunately rather widespread.
    NOTE: Reading agents and archivers preparing indexes of articles
    should bear in mind that user-chosen keywords are notoriously poor
    for indexing purposes unless the keywords are picked from a
    predefined set (which they are not in this case).  Also, some
    followup agents unwisely propagate the Keywords header from the
    precursor into the followup by default.  At least one news-based
    experiment has found the contents of Keywords headers to be
    completely valueless for indexing.

6.9. Summary

 The Summary header content is a short phrase summarizing the
 article's content:
    Summary-content = nonblank-text
 As with the subject, no restriction is placed on the content since it
 is intended solely for display to humans.
    NOTE: Reading agents should be aware that the Summary header is
    often used as a sort of secondary Subject header, and (if present)
    its contents should perhaps be displayed when the subject is
 The summary SHOULD be terse.  Posters SHOULD avoid trying to cram
 their entire article into the headers; even the simplest query
 usually benefits from a sentence or two of elaboration and context,
 and not all reading agents display all headers.

6.10. Approved

 The Approved header content indicates the mailing addresses (and
 possibly the full names) of the persons or entities approving the
 article for posting:

Spencer Historic [Page 53] RFC 1849 Son of 1036 March 2010

    Approved-content = From-content *( "," [ space ] From-content )
 An Approved header is required in all postings to moderated
 newsgroups; the presence or absence of this header allows a posting
 agent to distinguish between articles posted by the moderator (which
 are normal articles to be posted normally) and attempted
 contributions by others (which should be mailed to the moderator for
 approval).  An Approved header is also required in certain control
 messages, to reduce the probability of accidental posting of same;
 see the relevant parts of Section 7.
    NOTE: There is, at present, no way to authenticate Approved
    headers to ensure that the claimed approval really was bestowed.
    Nor is there an established mechanism for even maintaining a list
    of legitimate approvers (such a list would quickly become out of
    date if it had to be maintained by hand).  Such mechanisms,
    presumably relying on cryptographic authentication, would be a
    worthwhile extension to this Draft, and experimental work in this
    area is encouraged.  (The problem is harder than it sounds because
    news is used on many systems that do not have real-time access to
    key servers.)
    NOTE: Relayer implementors, please note well: it is the POSTING
    AGENT that is authorized to distinguish between moderator postings
    and attempted contributions, and to mail the latter to the
    moderator.  As discussed in Section 9.1, relayers MUST NOT, repeat
    MUST NOT, send such mail; on receipt of an unApproved article in a
    moderated newsgroup, they should discard the article, NOT
    transform it into a mail message (except perhaps to a local
    NOTE: [RFC1036] restricted Approved to a single From-content.
    However, multiple moderation is no longer rare, and multi-
    moderator Approved headers are already in use.

6.11. Lines

 The Lines header content indicates the number of lines in the body of
 the article:
    Lines-content = 1*digit
 The line count includes all body lines, including the signature (if
 any) and including empty lines (if any) at the beginning or end of
 the body.  (The single empty separator line between the headers and
 the body is not part of the body.)  The "body" here is the body as
 found in the posted article, AFTER all transformations such as MIME

Spencer Historic [Page 54] RFC 1849 Son of 1036 March 2010

 Reading agents SHOULD NOT rely on the presence of this header, since
 it is optional (and some posting agents do not supply it).  They MUST
 NOT rely on it being precise, since it frequently is not.
    NOTE: The average line length in article bodies is surprisingly
    consistent at about 40 characters, and since the line count
    typically is used only for approximate judgements ("is this too
    long to read quickly?"), dividing the byte count of the body by 40
    gives an estimate of the body line count that is adequate for
    normal use.  This estimate is NOT adequate if the body has been
    MIME encoded, but neither is the Lines header: at least one major
    relayer will add a Lines header to an article that lacks one,
    without considering the possibility of MIME encodings when
    computing the line count.
    NOTE: It would be better to have a Content-Size header as part of
    MIME, so that body parts could have their own sizes, and so that
    the units used could be appropriate to the data type (line count
    is not a useful measure of the size of an encoded image, for
    example).  Doing this is preferable to trying to fix Lines.
    UNRESOLVED ISSUE: Update on Content-Size?
 Relayers SHOULD discard this header if they find it necessary to
 re-encode the article in such a way that the original Lines header
 would be rendered incorrect.

6.12. Xref

 The Xref header content indicates where an article was filed by the
 last relayer to process it:
    Xref-content     = relayer 1*( space location )
    relayer          = relayer-name
    location         = newsgroup-name ":" article-locator
    article-locator  = 1*<ASCII printable character>
 The relayer's name is included so that software can determine which
 relayer generated the header (and specifically, whether it really was
 the one that filed the copy being examined).  The locations specify
 what newsgroups the article was filed under (which may differ from
 those in the Newsgroups header) and where it was filed under them.
 The exact form of an article locator is implementation-specific.
    NOTE: Reading agents can exploit this information to avoid
    presenting the same article to a reader several times.  The
    information is sometimes available in system databases, but having
    it in the article is convenient.  Relayers traditionally generate

Spencer Historic [Page 55] RFC 1849 Son of 1036 March 2010

    an Xref header only if the article is cross-posted, but this is
    not mandatory, and there is at least one new application
    ("mirroring": keeping news databases on two hosts identical) where
    the header is useful in all articles.
    NOTE: The traditional form of an article locator is a decimal
    number, with articles in each newsgroup numbered consecutively
    starting from 1.  NNTP [RFC977] demands that such a model be
    provided, and there may be other software that expects it, but it
    seems desirable to permit flexibility for unorthodox
 A relayer inserting an Xref header into an article MUST delete any
 previous Xref header.  A relayer that is not inserting its own Xref
 header SHOULD delete any previous Xref header.  A relayer MAY delete
 the Xref header when passing an article on to another relayer.
    NOTE: [RFC1036] specified that the Xref header was not transmitted
    when an article was passed to another relayer, but the major news
    implementations have never obeyed this rule, and applications like
    mirroring depend on this disobedience.
 A relayer MUST use the same name in Xref headers as it uses in Path
 headers.  Reading agents MUST ignore an Xref header containing a
 relayer name that differs from the one that begins the path list.

6.13. Organization

 The Organization header content is a short phrase identifying the
 poster's organization:
    Organization-content = nonblank-text
 This header is typically supplied by the posting agent.  The
 Organization content SHOULD mention geographical location (e.g., city
 and country) when it is not obvious from the organization's name.
    NOTE: The motive here is that the organization is often difficult
    to guess from the mailing address, is not always supplied in a
    signature, and can help identify the poster to the reader.
    NOTE: There is no "s" in "Organization".
 The Organization content is provided for identification only and does
 not imply that the poster speaks for the organization or that the
 article represents organization policy.  Posting agents SHOULD permit
 the poster to override a local default Organization header.

Spencer Historic [Page 56] RFC 1849 Son of 1036 March 2010

6.14. Supersedes

 The Supersedes header content specifies articles to be cancelled on
 arrival of this one:
    Supersedes-content = message-id *( space message-id )
 Supersedes is equivalent to Also-Control (Section 6.15) with an
 implicit verb of "cancel" (Section 7.1).
    NOTE: Supersedes is normally used where the article is an updated
    version of the one(s) being cancelled.
    NOTE: Although the ability to use multiple message IDs in
    Supersedes is highly desirable (see Section 7.1), posters are
    warned that existing implementations often do not correctly handle
    more than one.
    NOTE: There is no "c" in "Supersedes".
 An article with a Supersedes header MUST NOT have an Also-Control or
 Control header.

6.15. Also-Control

 The Also-Control header content marks the article as being a control
 message IN ADDITION to being a normal news article and specifies the
 desired actions:
    Also-Control-content = Control-content
 An article with an Also-Control header is filed and passed on
 normally, but the content of the Also-Control header is processed as
 if it were found in a Control header.
    NOTE: It is sometimes desirable to piggyback control actions on a
    normal article, so that the article will be filed normally but
    will also be acted on as a control message.  This header is
    essentially a generalization of Supersedes.
    NOTE: Be warned that some old relayers do not implement
 An article with an Also-Control header MUST NOT have a Control or
 Supersedes header.

Spencer Historic [Page 57] RFC 1849 Son of 1036 March 2010

6.16. See-Also

 The See-Also header content lists message IDs of articles that are
 related to this one but are not its precursors:
    See-Also-content = message-id *( space message-id )
 See-Also resembles References, but without the restrictions imposed
 on References by the followup rules.
    NOTE: See-Also provides a way to group related articles, such as
    the parts of a single document that had to be split across
    multiple articles due to its size, or to cross-reference between
    parallel threads.
    NOTE: See the discussion (in Section 6.5) on MAIL compatibility
    issues of References and See-Also.
    NOTE: In the specific case where it is desired to essentially make
    another article PART of the current one, e.g., for annotation of
    the other article, MIME's "message/external-body" convention can
    be used to do so without actual inclusion.  "news-message-ID" was
    registered as a standard external-body access method, with a
    mandatory NAME parameter giving the message ID and an optional
    SITE parameter suggesting an NNTP site that might have the article
    available (if it is not available locally), by IANA 22 June 1993.
    UNRESOLVED ISSUE: Could the syntax be generalized to include URLs
    as alternatives to message IDs?  Here it makes much more sense
    than in References.

6.17. Article-Names

 The Article-Names header content indicates any special significance
 the article may have in particular newsgroups:
    Article-Names-content  = 1*( name-clause space )
    name-clause            = newsgroup-name ":" article-name
    article-name           = letter 1*( letter / digit / "-" )
 Each name clause specifies a newsgroup (which SHOULD be among those
 in the Newsgroups header) and an article name local to that
 newsgroup.  Article names MAY be used by relayers to file the article
 in special ways, or they MAY just be noted for possible special
 attention by reading agents.  Article names are case-sensitive.

Spencer Historic [Page 58] RFC 1849 Son of 1036 March 2010

    NOTE: This header provides a way to mark special postings, such as
    introductions, frequently-asked-question lists, etc., so that
    reading agents have a way of finding them automatically.  The
    newsgroup name is specified for each article name because the
    names may be newsgroup-specific; for example, many frequently-
    asked-question lists are posted to "news.answers" in addition to
    their "home" newsgroup, and they would not be known by the same
    name(s) in both newsgroups.
 The Article-Names header SHOULD be ignored unless the article also
 contains an Approved header.
    NOTE: This stipulation is made in anticipation of the possibility
    that Approved headers will be involved in cryptographic
 The presence of an Article-Names header does not necessarily imply
 that the article will be retained unusually long before expiration,
 or that previous article(s) with similar Article-Names headers will
 be cancelled by its arrival.  Posters preparing special postings
 SHOULD include appropriate other headers, such as Expires and
 Supersedes, to request such actions.
 Different networks MAY establish different sets of article names for
 the special postings they deem significant; it is preferable for
 usage to be standardized within networks, although it might be
 desirable for individual newsgroups to have different naming
 conventions in some situations.  Article names MUST be 14 characters
 or less.  The following names are suggested but are not mandatory:
 intro       Introduction to the newsgroup for newcomers.
 charter     Charter, rules, organization, moderation policies, etc.
 background  Biographies of special participants, history of the
             newsgroup, notes on related newsgroups, etc.
 subgroups   Descriptions of sub-newsgroups under this newsgroup,
             e.g., "" under "".
 facts       Information relating to the purpose of the newsgroup,
             e.g., an acronym glossary in "".
 references  Where to get more information: books, journals, FTP
             repositories, etc.
 faq         Answers to frequently asked questions.

Spencer Historic [Page 59] RFC 1849 Son of 1036 March 2010

 menu        If present, a list of all of the other article names
             local to this newsgroup, with brief descriptions of their
 Such articles may be divided into subsections using the MIME
 "multipart/mixed" conventions.  If size considerations make it
 necessary to split such articles, names ending in a hyphen and a part
 number are suggested; for example, a three-part frequently-asked-
 questions list could have article names "faq-1", "faq-2", and
    NOTE: It is somewhat premature to attempt to standardize article
    names, since this is essentially a new feature with no experience
    behind it.  However, if reading agents are to attach special
    significance to these names, some attempt at standard conventions
    is imperative.  This is a first attempt at providing some.

6.18. Article-Updates

 The Article-Updates header content indicates what previous articles
 this one is deemed (by the poster) to update (i.e., replace):
    Article-Updates-content  = message-id *( space message-id )
 Each message ID identifies a previous article that this one is deemed
 to update.  This MUST NOT cause the previous article(s) to be
 cancelled or otherwise altered, unless this is implied by other
 headers (e.g., Supersedes); Article-Updates is merely an advisory
 that MAY be noted for special attention by reading agents.
    NOTE: This header provides a way to mark articles that are only
    minor updates of previous ones, containing no significant new
    information and not worth reading if the previous ones have been
    NOTE: If suitable conventions using MIME multipart bodies and the
    "message/external-body" body-part type can be developed, a
    replacing article might contain only differences between the old
    text and the new text, rather than a complete new copy.  This is
    the motivation for not making Article-Updates also function as
    Supersedes does: the replacing article might depend on the
    continued presence of the replaced article.

7. Control Messages

 The following sections document the currently defined control
 messages.  "Message" is used herein as a synonym for "article" unless
 context indicates otherwise.

Spencer Historic [Page 60] RFC 1849 Son of 1036 March 2010

 Posting agents are warned that since certain control messages require
 article bodies in quite specific formats, signatures SHOULD NOT be
 appended to such articles, and it may be wise to take greater care
 than usual to avoid unintended (although perhaps well-meaning)
 alterations to text supplied by the poster.  Relayers MUST assume
 that control messages mean what they say; they MAY be obeyed as is or
 rejected, but MUST NOT be reinterpreted.
 The execution of the actions requested by control messages is subject
 to local administrative restrictions, which MAY deny requests or
 refer them to an administrator for approval.  The descriptions below
 are generally phrased in terms suggesting mandatory actions, but any
 or all of these MAY be subject to local administrative approval
 (either as a class or case-by-case).  Analogously, where the
 description below specifies that a message or portion thereof is to
 be ignored, this action MAY include reporting it to an administrator.
    NOTE: The exact choice of local action might depend on what action
    the control message requests, who it claims to come from, etc.
 Relayers MUST propagate even control messages they do not understand.
 In the following sections, each type of control message is defined
 syntactically by defining its arguments and its body.  For example,
 "cancel" is defined by defining cancel-arguments and cancel-body.

7.1. cancel

 The cancel message requests that one or more previous articles be
    cancel-arguments  = message-id *( space message-id )
    cancel-body       = body
 The argument(s) identify the articles to be cancelled, by message ID.
 The body is a comment, which software MUST ignore, and SHOULD contain
 an indication of why the cancellation was requested.  The cancel
 message SHOULD be posted to the same newsgroup(s), with the same
 distribution(s), as the article(s) it is attempting to cancel.
    NOTE: Using the same newsgroups and distributions maximizes the
    chances of the cancel message propagating everywhere the target
    articles went.
    NOTE: [RFC1036] permitted only a single message-id in a cancel
    message.  Support for cancelling multiple articles is highly
    desirable, especially for use with Supersedes (see Section 6.14).
    If several revisions of an article appear in fast succession, each

Spencer Historic [Page 61] RFC 1849 Son of 1036 March 2010

    using Supersedes to cancel the previous one, it is possible for a
    middle revision to be destroyed by cancellation before it is
    propagated onward to cancel its predecessor.  Allowing each
    article to cancel several predecessors greatly alleviates this
    problem.  (Posting agents preparing a cancel of an article that
    itself cancels other articles might wish to add those articles to
    the cancel-arguments.)  However, posters should be aware that much
    old software does not implement multiple cancellation properly and
    should avoid using it when reliable cancellation is vitally
 When an article (the "target article") is to be cancelled, there are
 four cases of interest: the article hasn't arrived yet, it has
 arrived and been filed and is available for reading, it has expired
 and been archived on some less-accessible storage medium, or it has
 expired and been deleted.  The next few paragraphs discuss each case
 in turn (in reverse order, which is convenient for the explanation).
 EXPIRED AND DELETED.  Take no action.
 EXPIRED AND ARCHIVED.  If the article is readily accessible and can
 be deleted or made unreadable easily, treat as under AVAILABLE below.
 Otherwise, treat as under EXPIRED AND DELETED.
    NOTE: While it is desirable for archived articles to be
    cancellable, this can easily involve rewriting an entire archive
    volume just to get rid of one article, perhaps with manual actions
    required to arrange it.  It is difficult to envision a situation
    so dire as to require such measures from hundreds or thousands of
    administrators, or for that matter one in which widespread
    compliance with such a request is likely.
 AVAILABLE.  Compare the mailing addresses from the From lines of the
 cancel message and the target article, bearing in mind that local
 parts (except for "postmaster") are case-sensitive and domains are
 case-insensitive.  If they do not match, either refer the issue to an
 administrator for a case-by-case decision, or treat as if they
    NOTE: It is generally trivial to forge articles, so nothing short
    of cryptographic authentication is really adequate to ensure that
    a cancel came from the original article's author.  Moreover, it is
    highly desirable to permit authorities other than the author to
    cancel articles, to allow for cases in which the author is
    unavailable, uncooperative, or malicious, and in which damage
    and/or legal problems may be minimized by prompt cancellation.

Spencer Historic [Page 62] RFC 1849 Son of 1036 March 2010

    Reliable authentication that would permit such administrative
    cancels would be a worthwhile extension to this Draft, and
    experimental work in this area is encouraged.
    NOTE: Meanwhile, a simple check of addresses is useful accident
    prevention and catches at least the most simple-minded forgers.
    Since the intent is accident prevention rather than ironclad
    security, use of the From address is appropriate, all the more so
    because in the presence of gateways (especially redundant multiple
    gateways), the author may not have full control over Sender
    NOTE: The "refer... or treat as if they matched" rule is intended
    to specifically forbid quietly ignoring cancels with mismatched
 If the addresses match, then if technically possible, the relayer
 MUST delete the target article completely and immediately.  Failing
 that, it MUST make the target article unreadable (preferably to
 everyone, minimally to everyone but the administrator) and either
 arrange for it to be deleted as soon as possible or notify an
 administrator at once.
    NOTE: To allow for events such as criminal actions, malicious
    forgeries, and copyright infringements, where damage and/or legal
    problems may be minimized by prompt cancellation, complete removal
    is strongly preferred over merely making the target article
    unreadable.  The potential for malice is outweighed by the
    importance of really getting rid of the target article in some
    legitimate cases.  (In cases of inadvertent copyright violation in
    particular, the ability to quickly remedy the violation is of
    considerable legal importance.)  Failing that, making it
    unreadable is better than nothing.
    NOTE: Merely annotating the article so that readers see an
    indication that the author wanted it cancelled is not acceptable.
    Making the article unreadable is the minimum action.
    NOTE: There have been experiments with making cancelled articles
    unreadable, so that local news administrators could reverse
    cancellations.  In practice, administrators almost never find
    cause to do so.  Removal appears to be clearly preferable where
    technically feasible.

Spencer Historic [Page 63] RFC 1849 Son of 1036 March 2010

 NOT ARRIVED YET.  If practical, retain the cancel message until the
 target article does arrive, or until there is no further possibility
 of it arriving and being accepted (see Section 9.2), and then treat
 as under AVAILABLE.  Failing that, arrange for the target article to
 be rejected and discarded if it does arrive.
    NOTE: It may well be impractical to retain the control message,
    given uncertainty about whether the target article will ever
    arrive.  Existing practice in such cases is to assume that
    addresses would match and arrange the equivalent of deletion.
    This is often done by making a spurious entry in a database of
    already-seen message IDs (see Section 9.3), so that if the article
    does arrive, it will be rejected as a duplicate.
 The cancel message MUST be propagated onward in the usual fashion,
 regardless of which of the four cases applied, so that the target
 article will be cancelled everywhere even if cancellation and target
 article follow different routes.
    NOTE: [RFC1036] appeared to require stopping cancel propagation in
    the NOT ARRIVED YET case, although the wording was somewhat
    unclear.  This appears to have been an unwise decision; there are
    known cases of important cancellations (in situations of
    inadvertent copyright violation, for example) achieving rather
    poorer propagation than the target article.  News propagation is
    often a much less orderly process than the authors of [RFC1036]
    apparently envisioned.  Modern implementations generally propagate
    the cancellation regardless.
 Posting agents meant for use by ordinary posters SHOULD reject an
 attempt to post a cancel message if the target article is available
 and the mailing address in its From header does not match the one in
 the cancel message's From header.
    NOTE: This, again, is primarily accident prevention.

7.2. ihave, sendme

 The ihave and sendme control messages implement a crude batched
 predecessor of the NNTP [RFC977] protocol.  They are largely obsolete
 in the Internet but still see use in the UUCP environment, especially
 for backup feeds that normally are active only when a primary feed
 path has failed.
    NOTE: The ihave and sendme messages defined here have ABSOLUTELY
    NOTHING TO DO WITH NNTP, despite similarities of terminology.

Spencer Historic [Page 64] RFC 1849 Son of 1036 March 2010

 The two messages share the same syntax:
    ihave-arguments   = *( message-id space ) relayer-name
    sendme-arguments  = ihave-arguments
    ihave-body        = *( message-id eol )
    sendme-body       = ihave-body
 Message IDs MUST appear in either the arguments or the body, but not
 both.  Relayers SHOULD generate the form putting message IDs in the
 body, but the other form MUST be supported for backward
    NOTE: [RFC1036] made the relayer name optional, but difficulties
    could easily ensue in determining the origin of the message, and
    this option is believed to be unused nowadays.  Putting the
    message IDs in the body is strongly preferred over putting them in
    the arguments because it lends itself much better to large numbers
    of message IDs and avoids the empty-body problem mentioned in
    Section 4.3.1.
 The ihave message states that the named relayer has filed articles
 with the specified message IDs, which may be of interest to the
 relayer(s) receiving the ihave message.  The sendme message requests
 that the relayer receiving it send the articles having the specified
 message IDs to the named relayer.
 These control messages are normally sent essentially as point-to-
 point messages, by using "to." newsgroups (see Section 5.5) that are
 sent only to the relayer for which the messages are intended.  The
 two relayers MUST be neighbors, exchanging news directly with each
 other.  Each relayer advertises its new arrivals to the other using
 ihave messages, and each uses sendme messages to request the articles
 it lacks.
    NOTE: Arguably these point-to-point control messages should flow
    by some other protocol, e.g., mail, but administrative and
    interfacing issues are simplified if the news system doesn't need
    to talk to the mail system.
 To reduce overhead, ihave and sendme messages SHOULD be sent
 relatively infrequently and SHOULD contain substantial numbers of
 message IDs.  If ihave and sendme are being used to implement a
 backup feed, it may be desirable to insert a delay between reception
 of an ihave and generation of a sendme, so that a slightly slow
 primary feed will not cause large numbers of articles to be requested
 unnecessarily via sendme.

Spencer Historic [Page 65] RFC 1849 Son of 1036 March 2010

7.3. newgroup

 The newgroup control message requests that a new newsgroup be
    newgroup-arguments  = newsgroup-name [ space moderation ]
    moderation          = "moderated" / "unmoderated"
    newgroup-body       = body
                        / [ body ] descriptor [ body ]
    descriptor          = descriptor-tag eol description-line eol
    descriptor-tag      = "For your newsgroups file:"
    description-line    = newsgroup-name space description
    description         = nonblank-text [ " (Moderated)" ]
 The first argument names the newsgroup to be created, and the second
 one (if present) indicates whether it is moderated.  If there is no
 second argument, the default is "unmoderated".
    NOTE: Implementors are warned that there is occasional use of
    other forms in the second argument.  It is suggested that such
    violations of this Draft, which are also violations of [RFC1036],
    cause the newgroup message to be ignored. [RFC1036] was slightly
    vague about how second arguments other than "moderated" were to be
    treated (specifically, whether they were illegal or just ignored),
    but it is thought that all existing major implementations will
    handle "unmoderated" correctly, and it appears desirable to
    tighten up the specs to make it possible for other forms to be
    used in future.
 The body is a comment, which software MUST ignore, except that if it
 contains a descriptor, the description line is intended to be
 suitable for addition to a list of newsgroup descriptions.  The
 description cannot be continued onto later lines but is not
 constrained to any particular length.  Moderated newsgroups have
 descriptions that end with the string " (Moderated)" (note that this
 string begins with a blank).
    NOTE: It is unfortunate that the description line is part of the
    body, rather than being supplied in a header, but this is
    established practice.  Newsgroup creators are cautioned that the
    descriptor tag must be reproduced exactly as given above, must be
    alone on a line, and that it is case-sensitive.  (To reduce errors
    in this regard, posting agents might wish to question or reject
    newgroup messages that do not contain a descriptor.)  Given the
    desire for short lines, description writers should avoid content-
    free phrases like "discussion of" and "news about", and stick to
    defining what the newsgroup is about.

Spencer Historic [Page 66] RFC 1849 Son of 1036 March 2010

 The remainder of the body SHOULD contain an explanation of the
 purpose of the newsgroup and the decision to create it.
    NOTE: Criteria for newsgroup creation vary widely and are outside
    the scope of this Draft, but if formal procedures of one kind or
    another were followed in the decision, the body should mention
    this.  Administrators often look for such information when
    deciding whether to comply with creation/deletion requests.
 A newgroup message that lacks an Approved header MUST be ignored.
    NOTE: It would also be desirable to ignore a newgroup message
    unless its Approved header names a person who is authorized (in
    some sense) to create such a newsgroup.  A cooperating subnet with
    sufficiently strong coordination to maintain a correct and current
    list of authorized creators might wish to do so for its internal
    newsgroups.  It also (or alternatively) might wish to ignore a
    newgroup message for an internal newsgroup that was posted (or
    cross-posted) to a non-internal newsgroup.
    NOTE: As mentioned in Section 6.10, some form of (cryptographic?)
    authentication of Approved headers would be highly desirable,
    especially for control messages.
 It would be desirable to provide some way of supplying a moderator's
 address in a newgroup message for a moderated newsgroup, but this
 will cause problems unless effective authentication is available, so
 it is left for future work.
    NOTE: This leaves news administrators stuck with the annoying
    chore of arranging proper mailing of moderated-newsgroup
    submissions.  On Usenet, this can be simplified by exploiting a
    forwarding facility that some major sites provide: they maintain
    forwarding addresses, each the name of a moderated newsgroup with
    all periods (".", ASCII 46) replaced by hyphens ("-", ASCII 45),
    which forward mail to the current newsgroup moderators.  More
    advice on the subject of forwarding to moderators can be found in
    the document titled "How to Construct the Mailpaths File", posted
    regularly to the Usenet newsgroups news.lists, news.admin.misc,
    and news.answers.
 A newgroup message naming a newsgroup that already exists is
 requesting a change in the moderation status or description of the
 newsgroup.  The same rules apply.

Spencer Historic [Page 67] RFC 1849 Son of 1036 March 2010

7.4. rmgroup

 The rmgroup message requests that a newsgroup be deleted:
    rmgroup-arguments  = newsgroup-name
    rmgroup-body       = body
 The sole argument is the newsgroup name.  The body is a comment,
 which software MUST ignore; it SHOULD contain an explanation of the
 decision to delete the newsgroup.
    NOTE: Criteria for newsgroup deletion vary widely and are outside
    the scope of this Draft, but if formal procedures of one kind or
    another were followed in the decision, the body should mention
    this.  Administrators often look for such information when
    deciding whether to comply with creation/deletion requests.
 A rmgroup message that lacks an Approved header MUST be ignored.
    NOTE: It would also be desirable to ignore a rmgroup message
    unless its Approved header names a person who is authorized (in
    some sense) to delete such a newsgroup.  A cooperating subnet with
    sufficiently strong coordination to maintain a correct and current
    list of authorized deleters might wish to do so for its internal
    newsgroups.  It also (or alternatively) might wish to ignore a
    rmgroup message for an internal newsgroup that was posted (or
    cross-posted) to a non-internal newsgroup.
 Unexpected deletion of a newsgroup being a disruptive action,
 implementations are strongly advised to refer rmgroup messages to an
 administrator by default, unless perhaps the message can be
 determined to have originated within a cooperating subnet whose
 members are considered trustworthy.  Abuses have occurred.

7.5. sendsys, version, whogets

 The sendsys message requests that a description of the relayer's news
 feeds to other relayers be mailed to the article's reply address:
    sendsys-arguments  = [ relayer-name ]
    sendsys-body       = body
 If there is an argument, relayers other than the one named by the
 argument MUST NOT respond.  The body is a comment, which software
 MUST ignore; it SHOULD contain an explanation of the reason for the

Spencer Historic [Page 68] RFC 1849 Son of 1036 March 2010

 The version message requests that the name and version of the relayer
 software be mailed to the reply address:
    version-arguments  =
    version-body       = body
 There are no arguments.  The body is a comment, which software MUST
 ignore; it SHOULD contain an explanation of the reason for the
 The whogets message requests that a description of the relayer and
 its news feeds to other relayers be mailed to the article's reply
    whogets-arguments  = newsgroup-name [ space relayer-name ]
    whogets-body       = body
 The first argument is the name of the "target newsgroup", specifying
 the newsgroup for which propagation information is desired.  This
 MUST be a complete newsgroup name, not the name of a hierarchy or a
 portion of a newsgroup name that is not itself the name of a
 newsgroup.  If there is a second argument, only the relayer named by
 that argument should respond.  The body is a comment, which software
 MUST ignore; it SHOULD contain an explanation of the reason for the
    NOTE: Whogets is intended as a replacement for sendsys (and
    version) with a precisely specified reply format.  Since the
    syntax for specifying what newsgroups get sent to what other
    relayers varies widely between different forms of relayer
    software, the only practical way to standardize the reply format
    is to indicate a specific newsgroup and ask where THAT newsgroup
    propagates.  The requirement that it be a complete newsgroup name
    is intended to (largely) avoid the problem of having to answer
    "yes and no" in cases where not all newsgroups in a hierarchy are
 Any of these messages lacking an Approved header MUST be ignored.
 Response to any of these messages SHOULD be delayed for at least
 24 hours, and no response should be attempted if the message has been
 cancelled in that time.  Also, no response SHOULD be attempted unless
 the local part of the destination address is "newsmap".  News
 administrators SHOULD arrange for mail to "newsmap" on their systems
 to be discarded (without reply) unless legitimate use is in progress.
    NOTE: Because these messages can cause many, many relayers to send
    mail to one person, such messages, specifying mailing to an
    innocent person's mailbox, have been forged as a half-witted

Spencer Historic [Page 69] RFC 1849 Son of 1036 March 2010

    practical joke.  A delay gives administrators time to notice a
    fraudulent message and act (by cancelling the message, preparing
    to divert the flood of mail into the bit bucket, or both).
    Restriction of the destination address to "newsmap" reduces the
    appeal of fraud by making it impossible to use it to harass a
    normal user.  (A site that does NOT discard mail to "newsmap", but
    rather bounces it back, may incur higher communications costs than
    if the mail had been accepted into a user's mailbox, but a
    malicious forger could accomplish this anyway, by using an address
    whose local part is very unlikely to be a legitimate mailbox
    NOTE: [RFC1036] did not require the Approved header for these
    control messages.  This has been added because of the possibility
    that cryptographic authentication of Approved headers will become
 The body of the reply to a sendsys message SHOULD be of the form:
    sendsys-reply      = responder 1*sys-line
    responder          = "Responding-System:" space domain eol
    sys-line           = relayer-name ":" newsgroup-patterns
                                 [ ":" text ] eol
    newsgroup-patterns = newsgroup-name *( "," newsgroup-name )
 The first line identifies the responding system, using a syntax
 resembling a header (but note that it is part of the BODY).
 Remaining lines indicate what newsgroups are sent to what other
 systems.  The syntax of newsgroup patterns is not well standardized;
 the form described is common (often with newsgroup names only
 partially given, denoting all names starting with a particular set of
 components) but not universal.  The whogets message provides a
 better-defined alternative.
 The reply to a version message is of somewhat ill-defined form, with
 a body normally consisting of a single line of text that somehow
 describes the version of the relayer software.  The whogets message
 provides a better-defined alternative.

Spencer Historic [Page 70] RFC 1849 Son of 1036 March 2010

 The body of the reply to a whogets message MUST be of the form:
    whogets-reply      = responder-domain responder-relayer
                         response-date responding-to arrived-via
                         responder-version whogets-delimiter
    responder-domain   = "Responding-System:" space domain eol
    responder-relayer  = "Responding-Relayer:" space relayer-name eol
    response-date      = "Response-Date:" space date eol
    responding-to      = "Responding-To:" space message-id eol
    arrived-via        = "Arrived-Via:" path-list eol
    responder-version  = "Responding-Version:" space nonblank-text eol
    whogets-delimiter  = eol
    pass-line          = relayer-name [ space domain ] eol
 The first six lines identify the responding relayer by its Internet
 domain name (use of the ".uucp" and ".bitnet" pseudo-domains is
 permissible, for registered hosts in them, but discouraged) and its
 relayer name; specify the date when the reply was generated and the
 message ID of the whogets message being replied to; give the path
 list (from the Path header) of the whogets message (which MAY, if
 absolutely necessary, be truncated to a convenient length, but MUST
 contain at least the leading three relayer names); and indicate the
 version of relayer software responding.  Note that these lines are
 part of the BODY even though their format resembles that of headers.
 Despite the apparently fixed order specified by the syntax above,
 they can appear in any order, but there must be exactly one of each.
 After those preliminaries, and an empty line to unambiguously define
 their end, the remaining lines are the relayer names (which MAY be
 accompanied by the corresponding domain names, if known) of systems
 to which the responding system passes the target newsgroup.  Only the
 names of news relayers are to be included.
    NOTE: It is desirable for a reply to identify its source by both
    domain name and relayer name because news propagation is governed
    by the latter but location in a broader context is best determined
    by the former.  The date and whogets message ID should, in
    principle, be present in the MAIL headers but are included in the
    body for robustness in the presence of uncooperative mail systems.
    The reason for the path list is discussed below.  Adding version
    information eliminates the need for a separate message to gather

Spencer Historic [Page 71] RFC 1849 Son of 1036 March 2010

    NOTE: The limitation of pass lines to contain only names of news
    relayers is meant to exclude names used within a single host (as
    identifiers for mail gateways, portions of ihave/sendme
    implementations, etc.), which do not actually refer to other
 A relayer that is unaware of the existence of the target newsgroup
 MUST NOT reply to a whogets message at all, although this MUST NOT
 influence decisions on whether to pass the article on to other
    NOTE: While this may result in discontinuous maps in cases where
    some hosts have not honored requests for creation of a newsgroup,
    it will also prevent a flood of useless responses in the event
    that a whogets message intended to map a small region "leaks" out
    to a larger one.  The possibility of discontinuous recognition of
    a newsgroup does make it important that the whogets message itself
    continue to propagate (if other criteria permit).  This is also
    the reason for the inclusion of the whogets message's path list,
    or at least the leading portion of it, in the reply: to permit
    reconstruction of at least small gaps in maps.
 Different networks set different rules for the legitimacy of these
 messages, given that they may reveal details of organization-internal
 topology that are sometimes considered proprietary.
    NOTE: On Usenet, in particular, willingness to respond to these
    messages is held to be a condition of network membership: the
    topology of Usenet is public information.  Organizations wishing
    to belong to such networks while keeping their internal topology
    confidential might wish to organize their internal news software
    so that all articles reaching outsiders appear to be from a single
    "gatekeeper" system, with the details of internal topology hidden
    behind that system.
    UNRESOLVED ISSUE: It might be useful to have a way to set some
    sort of hop limit for these.

Spencer Historic [Page 72] RFC 1849 Son of 1036 March 2010

7.6. checkgroups

 The checkgroups control message contains a supposedly authoritative
 list of the valid newsgroups within some subset of the newsgroup name
    checkgroups-arguments  =
    checkgroups-body       = [ invalidation ] valid-groups
                           / invalidation
    invalidation           = "!" plain-component
                             *( "," plain-component ) eol
    valid-groups           = 1*( description-line eol )
 There are no arguments.  The body lines (except possibly for an
 initial invalidation) each contain a description line for a
 newsgroup, as defined under the newgroup message (Section 7.3).
    NOTE: Some other, ill-defined, forms of the checkgroups body were
    formerly used.  See Appendix A.
 The checkgroups message applies to all hierarchies containing any of
 the newsgroups listed in the body.  The checkgroups message asserts
 that the newsgroups it lists are the only newsgroups in those
 hierarchies.  If there is an invalidation, it asserts that the
 hierarchies it names no longer contain any newsgroups.
 Processing a checkgroups message MAY cause a local list of newsgroup
 descriptions to be updated.  It SHOULD also cause the local lists of
 newsgroups (and their moderation statuses) in the mentioned
 hierarchies to be checked against the message.  The results of the
 check MAY be used for automatic corrective action or MAY be reported
 to the news administrator in some way.
    NOTE: Automatically updating descriptions of existing newsgroups
    is relatively safe.  In the case of newsgroup additions or
    deletions, simply notifying the administrator is generally the
    wisest action, unless perhaps the message can be determined to
    have originated within a cooperating subnet whose members are
    considered trustworthy.
    NOTE: There is a problem with the checkgroups concept: not all
    newsgroups in a hierarchy necessarily propagate to the same set of
    machines.  (Notably, there is a set of newsgroups known as the
    "inet" newsgroups, which have relatively limited distribution but
    coexist in several hierarchies with more widely distributed
    newsgroups.)  The advice of checkgroups should always be taken
    with a grain of salt and should never be followed blindly.

Spencer Historic [Page 73] RFC 1849 Son of 1036 March 2010

8. Transmission Formats

 While this Draft does not specify transmission methods, except to
 place a few constraints on them, there are some data formats used
 only for transmission that are unique to news.

8.1. Batches

 For efficient bulk transmission and processing of news articles, it
 is often desirable to transmit a number of them as a single block of
 data, i.e., a "batch".  The format of a batch is:
    batch         = 1*( batch-header article )
    batch-header  = "#! rnews " article-size eol
    article-size  = 1*digit
 A batch is a sequence of articles, each prefixed by a header line
 that includes its size.  The article size is a decimal count of the
 octets in the article, counting each EOL as one octet regardless of
 how it is actually represented.
    NOTE: A relayer might wish to accept either a single article or a
    batch as input.  Since "#" cannot appear in a header name,
    examination of the first octet of the input will reveal its
    NOTE: In the header line, there is exactly one blank before
    "rnews", there is exactly one blank after "rnews", and the EOL
    immediately follows the article size.  Beware that some software
    inserts non-standard trash after the size.
    NOTE: Despite the similarity of this format to the executable-
    script format used by some operating systems, it is EXTREMELY
    unwise to just feed incoming batches to a command interpreter in
    the anticipation that it will run a command named "rnews" to
    process the batch.  Unless arrangements are made to very tightly
    restrict the range of commands that can be executed by this means,
    the security implications are disastrous.

Spencer Historic [Page 74] RFC 1849 Son of 1036 March 2010

8.2. Encoded Batches

 When transmitting news, especially over communications links that are
 slow or are billed by the bit, it is often desirable to batch news
 and apply data compression to the batches.  Transmission links
 sending compressed batches SHOULD use out-of-band means of
 communication to specify the compression algorithm being used.  If
 there is no way to send out-of-band information along with a batch,
 the following encapsulation for a compressed batch MAY be used:
       ec-batch             = "#! " compression-keyword eol
       compression-keyword  = "cunbatch"
 A line containing a keyword indicating the type of compression is
 followed by the compressed batch.  The only truly widespread
 compression keyword at present is "cunbatch", indicating compression
 using the widely distributed "compress" program.  Other compression
 keywords MAY be used by mutual agreement between the hosts involved.
    NOTE: An encapsulated compressed batch is NOT, in general, a text
    file, despite having an initial text line.  This combination of
    text and non-text data is often awkward to handle; for example,
    standard decompression programs cannot be used without first
    stripping off the initial line, and that in turn is painful to do
    because many text-handling tools that are superficially suited to
    the job do not cope well with non-text data, hence the
    recommendation that out-of-band communication be used instead when
    NOTE: For UUCP transmission, where a batch is typically
    transmitted by invoking the remote command "rnews" with the batch
    as its input stream, a plausible out-of-band method for indicating
    a compression type would be to give a compression keyword in an
    option to "rnews", perhaps in the form:
    rnews -d decompressor
    where "decompressor" is the name of a decompression program (e.g.,
    "uncompress" for a batch compressed with "compress" or "gunzip"
    for a batch compressed with "gzip").  How this decompression
    program is located and invoked by the receiving relayer is
    NOTE: See the notes in Section 8.1 on the inadvisability of
    feeding batches directly to command interpreters.

Spencer Historic [Page 75] RFC 1849 Son of 1036 March 2010

    NOTE: There is exactly one blank between "#!" and the compression
    keyword, and the EOL immediately follows the keyword.

8.3. News within Mail

 It is often desirable to transmit news as mail, either for the
 convenience of a human recipient or because that is the only type of
 transmission available on a restrictive communication path.
 Given the similarity between the news format and the MAIL format, it
 is superficially attractive to just send the news article as a mail
 message.  This is typically a mistake: mail-handling software often
 feels free to manipulate various headers in undesirable ways (in some
 cases, such as Sender, such manipulation is actually mandatory), and
 mail transmission problems, etc. MUST be reported to the
 administrators responsible for the mail transmission rather than to
 the article's author.  In general, news sent as mail should be
 encapsulated to separate the MAIL headers and the news headers.
 When the intended recipient is a human, any convenient form of
 encapsulation may be used.  Recommended practice is to use MIME
 encapsulation with a content type of "message/news", given that news
 articles have additional semantics beyond what "message/rfc822"
    NOTE: "message/news" was registered as a standard subtype by IANA
    22 June 1993.
 When mail is being used as a transmission path between two relayers,
 however, a standard method is desirable.  Currently the standard
 method is to send the mail to an address whose local part is "rnews",
 with whatever MAIL headers are necessary for successful transmission.
 The news article (including its headers) is sent as the body of the
 mail message, with an "N" prepended to each line.
    NOTE: The "N" reduces the probability of an innocent line in a
    news article being taken as a magic command to mail software and
    makes it easy for receiving software to strip off any lines added
    by mail software (e.g., the trailing empty line added by some UUCP
    mail software).
 This method has its weaknesses.  In particular, it assumes that the
 mail transmission channel can transmit nearly arbitrary body text
 undamaged.  When mail is being used as a transmission path of last
 resort, however, the mail system often has inconvenient preconceived
 notions about the format of message bodies.  Various ad hoc encoding
 schemes have been used to avoid such problems.  The recommended
 method is to send a news article or batch as the body of a MIME mail

Spencer Historic [Page 76] RFC 1849 Son of 1036 March 2010

 message, using content type "application/news-transmission" and
 MIME's "base64" encoding (which is specifically designed to survive
 all known major mail systems).
    NOTE: In the process, MIME conventions could be used to fragment
    and reassemble an article that is too large to be sent as a single
    mail message over a transmission path that restricts message
    length.  In addition, the "conversions" parameter to the content
    type could be used to indicate what (if any) compression method
    has been used.  Also, the Content-MD5 header [RFC1544] can be used
    as a "checksum" to provide high confidence of detecting accidental
    damage to the contents.
    UNRESOLVED ISSUE: The "conversions" parameter no longer exists.
    What should be done about this, if anything?
    NOTE: It might look tempting to use a content type such as
    "message/X-netnews", but MIME bans non-trivial encodings of the
    entire body of messages with content type "message".  The intent
    is to avoid obscuring nested structure underneath encodings.  For
    inter-relayer news transmission, there is no nested structure of
    interest, and it is important that the entire article (including
    its headers, not just its body) be protected against the vagaries
    of intervening mail software.  This situation appears to fit the
    MIME description of circumstances in which "application" is the
    proper content type.
    NOTE: "application/news-transmission", with a "conversions"
    parameter, was registered as a standard subtype by IANA
    22 June 1993.
    UNRESOLVED ISSUE: The "conversions" parameter no longer exists in
    MIME.  What should we do about this?

8.4. Partial Batches

    UNRESOLVED ISSUE: The existing batch conventions assemble
    (potentially) many articles into one batch.  Handling very large
    articles would be substantially less troublesome if there was also
    a fragmentation convention for splitting a large article into
    several batches.  Is this worth defining at this time?

9. Propagation and Processing

 Most aspects of news propagation and processing are implementation-
 specific.  The basic propagation algorithms, and certain details of
 how they are implemented, nevertheless need to be standard.

Spencer Historic [Page 77] RFC 1849 Son of 1036 March 2010

 There are two important principles that news implementors (and
 administrators) need to keep in mind.  The first is the well-known
 Internet Robustness Principle:
    Be liberal in what you accept, and conservative in what you send.
 However, in the case of news there is an even more important
 principle, derived from a much older code of practice, the
 Hippocratic Oath (we will thus call this the Hippocratic Principle):
    First, do no harm.
 It is VITAL to realize that decisions that might be merely suboptimal
 in a smaller context can become devastating mistakes when amplified
 by the actions of thousands of hosts within a few hours.

9.1. Relayer General Issues

 Relayers MUST NOT alter the content of articles unnecessarily.  Well-
 intentioned attempts to "improve" headers, in particular, typically
 do more harm than good.  It is necessary for a relayer to prepend its
 own name to the Path content (see Section 5.6) and permissible for it
 to rewrite or delete the Xref header (see Section 6.12).  Relayers
 MAY delete the thoroughly obsolete headers described in Appendix A.3,
 although this behavior no longer seems useful enough to encourage.
 Other alterations SHOULD be avoided at all costs, as per the
 Hippocratic Principle.
    NOTE: As discussed in Section 2.3, tidying up the headers of a
    user-prepared article is the job of the posting agent, not the
    relayer.  The relayer's purpose is to move already-compliant
    articles around efficiently without damaging them.  Note that in
    existing implementations, specific programs may contain both
    posting-agent functions and relayer functions.  The distinction is
    that posting-agent functions are invoked only on articles posted
    by local posters, never on articles received from other relayers.
    NOTE: A particular corollary of this rule is that relayers should
    not add headers unless truly necessary.  In particular, this is
    not SMTP; do not add Received headers.
 Relayers MUST NOT pass non-conforming articles on to other relayers,
 except perhaps in a cooperating subnet that has agreed to permit
 certain kinds of non-conforming behavior.  This is a direct
 consequence of the Internet Robustness Principle.

Spencer Historic [Page 78] RFC 1849 Son of 1036 March 2010

 The two preceding paragraphs may appear to be in conflict.  What is
 to be done when a non-conforming article is received?  The Robustness
 Principle argues that it should be accepted but must not be passed on
 to other relayers while still non-conforming, and the Hippocratic
 Principle strongly discourages attempts at repair.  The conclusion
 that this appears to lead to is correct: a non-conforming article MAY
 be accepted for local filing and processing, or it MAY be discarded
 entirely, but it MUST NOT be passed on to other relayers.
 A relayer MUST NOT respond to the arrival of an article by sending
 mail to any destination, other than a local administrator, except by
 explicit prearrangement with the recipient.  Neither posting an
 article (other than certain types of control messages; see
 Section 7.5) nor being the moderator of a moderated newsgroup
 constitutes such prearrangement.  UNDER NO CIRCUMSTANCES WHATSOEVER
 may a relayer attempt to send mail to either an article's originator
 or a moderator.
    NOTE: Reporting apparent errors in message composition is the job
    of a posting agent, not a relayer.  The same is true of mailing
    moderated-newsgroup postings to moderators.  In networks of
    thousands of cooperating relayers, it is simply unacceptable for
    there to be any circumstance whatsoever that causes any
    significant fraction of them to simultaneously send mail to the
    same destination.  (Some control messages are exceptions, although
    perhaps ill-advised ones.)  What might, in a smaller network, be a
    useful notification or forwarding becomes a deluge of nearly
    identical messages that can bring mail software to its knees and
    severely inconvenience recipients.  Moderators, in particular,
    historically have suffered grievously from this.
 Notification of problems in incoming articles MAY go to local
 administrators, or at most (by prearrangement!)  to the
 administrators of the neighboring relayer(s) that passed on the
 problematic articles.
    NOTE: It would be desirable to notify the author that his posting
    is not propagating as he expects.  However, there is no known
    method for doing this that will scale up gracefully.  (In
    particular, "notify only if within N relayers of the originator"
    falls down in the presence of commercial news services like UUNET:
    there may be hundreds or thousands of relayers within a couple of
    hops of the originator.)  The best that can be done right now is
    to notify neighbors, in hopes that the word will eventually
    propagate up the line, or organize regional monitoring at major

Spencer Historic [Page 79] RFC 1849 Son of 1036 March 2010

 If it is necessary to alter an article, e.g., translate it to another
 character set or alter its EOL representation, strenuous efforts
 should be made to ensure that such transformations are reversible,
 and that relayers or other software that might wish to reverse them
 know exactly how to do so.
    NOTE: For example, a cooperating subnet that exchanges articles
    using a non-ASCII character set like EBCDIC should define a
    standard, reversible ASCII-EBCDIC mapping and take pains to see
    that it is used at all points where the subnet meets the outside.
    If the only reason for using EBCDIC is that the readers typically
    employ EBCDIC devices, it would be more robust to employ ASCII as
    the interchange format and do the transformation in the reading
    and posting agents.

9.2. Article Acceptance and Propagation

 When a relayer first receives an article, it must decide whether to
 accept it.  (This applies regardless of whether the article arrived
 by itself or as part of a batch, and in principle regardless of
 whether it originated as a local posting or as traffic from another
 relayer.)  In a cooperating subnet with well-controlled propagation
 paths, some of the tests specified here MAY be delegated to centrally
 located relayers; that is, relayers that can receive news ONLY via
 one of the central relayers might simplify acceptance testing based
 on the assumption that incoming traffic has already passed the full
 set of tests at a central relayer.
 The wording that follows is based on a model in which articles arrive
 on a relayer's host before acceptance tests are done.  However,
 depending on the degree of integration of the transport mechanisms
 and the relayer, some or all of these tests MAY be done before the
 article is actually transmitted, so that articles that definitely
 will not be accepted need not be transmitted at all.
 The wording that follows also specifies a particular order for the
 acceptance tests.  While this order is the obvious one, the tests MAY
 be done in any order.
 First, the relayer MUST verify that the article is a legal news
 article, with all mandatory headers present with legal contents.
    NOTE: This check in principle is done by the first relayer to see
    an article, so an article received from another relayer should
    always be legal, but there is enough old software still
    operational that this cannot be taken for granted; see the
    discussion of the Internet Robustness Principle in Section 9.1.

Spencer Historic [Page 80] RFC 1849 Son of 1036 March 2010

 Second, the relayer MUST determine whether it has already seen this
 article (identified by its message ID).  This is normally done by
 retaining a history of all article message IDs seen in the last
 N days, where the value of N is decided by the relayer's
 administrator but SHOULD be at least 7.  Since N cannot practically
 be infinite, articles whose Date content indicates that they are
 older than N days are declared "stale" and are deemed to have been
 seen already.
    NOTE: This check is important because news propagation topology is
    typically redundant, often highly so, and it is not at all
    uncommon for a relayer to receive the same article from several
    neighbors.  The history of already-seen message IDs can get quite
    large, hence, the desire to limit its length, but it is important
    that it be long enough that slowly propagating articles are not
    classed as stale.  News propagation within the Internet is
    normally very rapid, but when UUCP links are involved, end-to-end
    delays of several days are not rare, so a week is not a
    particularly generous minimum.
    NOTE: Despite generally more rapid propagation in recent times, it
    is still not unheard of for some propagation paths to be very
    slow.  This can introduce the possibility of old articles arriving
    again after they are gone from the history, hence the "stale"
 Third, the relayer MUST determine whether any of the article's
 newsgroups are "subscribed to" by the host, i.e., fit a description
 of what hierarchies or newsgroups the site wants to receive.
    NOTE: This check is significant because information on what
    newsgroups a relayer wishes to receive is often stored at its
    neighbors, who may not have up-to-date information or may simplify
    the rules for implementation reasons.  As a hedge against the
    possibility of missed or delayed newgroup control messages,
    relayers may wish to observe a notion of a newsgroup subscription
    that is independent of the list of newsgroups actually known to
    the relayer.  This would permit reception and relaying of articles
    in newsgroups that the relayer is not (yet) aware of, subject to
    more general criteria indicating that they are likely to be of
 Once an article has been accepted, it may be passed on to other
 relayers.  The fundamental news propagation rule is a flooding
 algorithm: on receiving and accepting an article, send it to all
 neighboring relayers not already in its path list that are sent its
 newsgroup(s) and distribution(s).

Spencer Historic [Page 81] RFC 1849 Son of 1036 March 2010

    NOTE: The path list's role in loop prevention may appear
    relatively unimportant, given that looping articles would
    typically be rejected as duplicates anyway.  However, the path
    list's role in preventing superfluous transmissions is not
    trivial.  In particular, the path list is the only thing that
    prevents relayer X, on receiving an article from relayer Y, from
    sending it back to Y again.  (Indeed, the usual symptom of
    confusion about relayer names is that incoming news loops back in
    this manner.)  The looping articles would be rejected as
    duplicates, but doubling the communications load on every news
    transmission path is not to be taken lightly!
 In general, relayers SHOULD NOT make propagation decisions by
 "anticipation": relayer X, noting that the article's path list
 already contains relayer Y, decides not to send it to relayer Z
 because X anticipates that Z will get the article by a better path.
 If that is generally true, then why is there a news feed from X to Z
 at all?  In fact, the "better path" may be running slowly or may be
 down.  News propagation is very robust precisely because some
 redundant transmission is done "just in case".  If it is imperative
 to limit unnecessary traffic on a path, use of NNTP [RFC977] or
 ihave/sendme (see Section 7.2) to pass articles only when necessary
 is better than arbitrary decisions not to pass articles at all.
 Anticipation is occasionally justified in special cases.  Such cases
 should involve both (1) a cooperating subnet whose propagation paths
 are well-understood and well-monitored, with failures and slowdowns
 noticed and dealt with promptly, and (2) a persistent pattern of
 heavy unnecessary traffic on a path that is either slow or costly.
 In addition, there should be some reason why neither NNTP nor
 ihave/sendme is suitable as a solution to the problem.

9.3. Administrator Contact

 It is desirable to have a standardized contact address for a
 relayer's administrators, in the spirit of the "postmaster" address
 for mail administrators.  Mail addressed to "newsmaster" on a
 relayer's host MUST go to the administrator(s) of that relayer.  Mail
 addressed to "usenet" on the relayer's host SHOULD be handled
 likewise.  Mail addressed to either address on other hosts using the
 same news database SHOULD be handled likewise.
    NOTE: These addresses are case-sensitive, although it would be
    desirable for sequences equivalent to them using case-insensitive
    comparison to be handled likewise.  While "newsmaster" seems the
    preferred network-independent address, by analogy to "postmaster",
    there is an existing practice of using "usenet" for this purpose,

Spencer Historic [Page 82] RFC 1849 Son of 1036 March 2010

    and so "usenet" should be supported if at all possible (especially
    on hosts belonging to Usenet!).  The address "news" is also
    sometimes used for purposes like this, but less consistently.

10. Gatewaying

 Gatewaying of traffic between news networks using this Draft and
 those using other exchange mechanisms can be useful but must be done
 cautiously.  Gateway administrators are taking on significant
 responsibilities and must recognize that the consequences of error
 can be quite serious.

10.1. General Gatewaying Issues

 This section will primarily address the problems of gatewaying
 traffic INTO news networks.  Little can be said about the other
 direction without some specific knowledge of the network(s) involved.
 However, the two issues are not entirely independent: if a non-news
 network is gatewayed into a news network at more than one point,
 traffic injected into the non-news network by one gateway may appear
 at another as a candidate for injection back into the news network.
 This raises a more general principle, the single most important issue
 for gatewaying:
    Above all, prevent loops.
 The normal loop prevention of news transmission is vitally dependent
 on the Message-ID header.  Any gateway that finds it necessary to
 remove this header, alter it, or supersede it (by moving it into the
 body) MUST take equally effective precautions against looping.
    NOTE: There are few things more effective at turning news readers
    into a lynch mob than a malfunctioning gateway, or pair of
    gateways, that takes in news articles, mangles them just enough to
    prevent news relayers from recognizing them as duplicates, and
    regurgitates them back into the news stream.  This happens rather
    too often.
 Gateway implementors should realize that gateways have all of the
 responsibilities of relayers, plus the added complications introduced
 by transformations between different information formats.  Much of
 the discussion in Section 9 about relayer issues is relevant to
 gateways as well.  In particular, gateways SHOULD keep a history of
 recently seen articles, as described in Section 9.2, and not assume
 that articles will never reappear.  This is particularly important
 for networks that have their own concept analogous to message IDs: a
 gateway should keep a history of traffic seen from BOTH directions.

Spencer Historic [Page 83] RFC 1849 Son of 1036 March 2010

 If at all possible, articles entering the non-news network SHOULD be
 marked in some way so that they will NOT be re-gatewayed back into
 news.  Multiple gateways obviously must agree on the marking method
 used; if it is done by having them know each others' names, name
 changes MUST be coordinated with great care.  If marking cannot be
 done, all transformations MUST be reversible so that a re-gatewayed
 article is identical to the original (except perhaps for a longer
 Path header).
 Gateways MUST NOT pass control messages (articles containing Control,
 Also-Control, or Supersedes headers) without removing the headers
 that make them control messages, unless there are compelling reasons
 to believe that they are relevant to both sides and that conventions
 are compatible.  If it is truly desirable to pass them unaltered,
 suitable precautions MUST be taken to ensure that there is NO
 POSSIBILITY of a looping control message.
    NOTE: The damage done by looping articles is multiplied a
    thousandfold if one of the affected articles is something like a
    sendsys message (see Section 7.5) that requests multiple automatic
    replies.  Most gateways simply should not pass control messages at
    all.  If some unusual reason dictates doing so, gateway
    implementors and administrators are urged to consider bulletproof
    rate-limiting measures for the more destructive ones like sendsys,
    e.g., passing only one per hour no matter how many are offered.
 Gateways, like relayers, SHOULD make determined efforts to avoid
 mangling articles unnecessarily.  In the case of gateways, some
 transformations may be inevitable, but keeping them to a minimum and
 ensuring that they are reversible is still highly desirable.
 Gateways MUST avoid destroying information.  In particular, the
 restrictions of Section 4.2.2 are best taken with a grain of salt in
 the context of gateways.  Information that does not translate
 directly into news headers SHOULD be retained, perhaps in "X-"
 headers, both because it may be of interest to sophisticated readers
 and because it may be crucial to tracing propagation problems.
 Gateway implementors should take particular note of the discussion of
 mailed replies, or more precisely the ban on same, in Section 9.1.
 Gateway problems MUST be reported to the local administration, not to
 the innocent originator of traffic.  "Gateway problems" here includes
 all forms of propagation anomaly on the non-news side of the gateway,
 e.g., unreachable addresses on a mailing list.  Note that this
 requires consideration of possible misbehavior of "downstream" hosts,
 not just the gateway host.

Spencer Historic [Page 84] RFC 1849 Son of 1036 March 2010

10.2. Header Synthesis

 News articles prepared by gateways MUST be legal news articles.  In
 particular, they MUST include all of the mandatory headers (see
 Section 5) and MUST fully conform to the restrictions on said
 headers.  This often requires that a gateway function not only as a
 relayer but also partly as a posting agent, aiding in the synthesis
 of a conforming article from non-conforming input.
    NOTE: The full-conformance requirement needs particularly careful
    attention when gatewaying mailing lists to news, because a number
    of constructs that are legal in MAIL headers are NOT permissible
    in news headers.  (Note also that not all mail traffic fully
    conforms to even the MAIL specification.)  The rest of this
    section will be phrased in terms of mail-to-news gatewaying, but
    most of it is more generally applicable.
 The mandatory headers generally present few problems.
 If no date information is available, the gateway should supply a Date
 header with the gateway's current date.  If only partial information
 is available (e.g., date but not time), this should be fleshed out to
 a full Date header by adding default values, not by mixing in parts
 of the gateway's current date.  (Defaults should be chosen so that
 fleshed-out dates will not be in the future!)  It may be necessary to
 map time zone information to the restricted forms permitted in the
 news Date header.  See Section 5.1.
    NOTE: The prohibition of mixing dates is on the theory that it is
    better to admit ignorance than to lie.
 If the author's address as supplied in the original message is not
 suitable for inclusion in a From header, the gateway MUST transform
 it so it is (for example, by use of the "% hack" and the domain
 address of the gateway).  The desire to preserve information is NOT
 an excuse for violating the rules.  If the transformation is drastic
 enough that there is reason to suspect loss of information, it may be
 desirable to include the original form in an "X-" header, but the
 From header's contents MUST be as specified in Section 5.2.
 If the message contains a Message-ID header, the contents should be
 dealt with as discussed in Section 10.3.  If there is no message ID
 present, it will be necessary to synthesize one, following the news
 rules (see Section 5.3).
 Every effort should be made to produce a meaningful Subject header;
 see Section 5.4.  Many news readers select articles to read based on
 Subject headers, and inserting a placeholder like "<no subject

Spencer Historic [Page 85] RFC 1849 Son of 1036 March 2010

 available>" is considered highly objectionable.  Even synthesizing a
 Subject header by picking out the first half-dozen nouns and
 adjectives in the article body is better than using a placeholder,
 since it offers SOME indication of what the article might contain.
 The contents of the Newsgroups header (Section 5.5) are usually
 predetermined by gateway configuration, but a gateway to a network
 that has its own concept of newsgroups or discussions might have to
 make transformations.  Such transformations should be reversible;
 otherwise, confusion is likely on both sides.
 It will rarely be possible for gateways to provide a Path header that
 is both an accurate history of the relayers the article has passed
 through AS NEWS and a usable reply address.  The history function
 MUST be given priority; see the discussion in Section 5.6.  It will
 usually be necessary for a gateway to supply an empty path list,
 abandoning the reply function.
 It is desirable for gatewayed articles to convey as much useful
 information as possible, e.g., by use of optional news headers (see
 Section 6) when the relevant information is available.  Synthesis of
 optional headers can generally follow similar rules.
 Software synthesizing References headers should note the discussion
 in Section 6.5 concerning the incompatibility between MAIL and news.
 Also of interest is the possibility of incorporating information from
 In-Reply-To headers and from attribution lines in the body; an
 incomplete or somewhat conjectural References header is much better
 than none at all, and reading agents already have to cope with
 incomplete or slightly erroneous References lists.

10.3. Message ID Mapping

 This section, like the previous one, is phrased in terms of mail
 being gatewayed into news, but most of the discussion should be more
 generally applicable.
 A particularly sticky problem of gatewaying mail into news is
 supplying legal news message IDs.  Note, in particular, that not all
 MAIL message IDs are legal in news; the news syntax (specified in
 Section 5.3, with related material in Section 5.2) is more
 restrictive.  Generating a fully conforming news article from a mail
 message may require transforming the message ID somewhat.
 Generation and transformation of message IDs assumes particular
 importance if a given mailing list (or whatever) is being handled by
 more than one gateway.  It is highly desirable that the same article
 contents not appear twice in the same newsgroup, which requires that

Spencer Historic [Page 86] RFC 1849 Son of 1036 March 2010

 they receive the same message ID from all gateways.  Gateways SHOULD
 use the following algorithm (possibly modified by the later
 discussion of gatewaying into more than one newsgroup) unless local
 considerations dictate another:
    1. Separate message ID from surroundings, if necessary.  A
       plausible method for this is to start at the first "<", end at
       the next ">", and reject the message if no ">" is found or a
       second "<" is seen before the ">".  Also reject the message if
       the message ID contains no "@" or more than one "@", or if it
       contains no ".".  Also reject the message if the message ID
       contains non-ASCII characters, ASCII control characters, or
       white space.
          NOTE: Any legitimate domain will include at least one ".".
          [RFC822], Section 6.2.2, forbids white space in this context
          when passing mail on to non-MAIL software.
    2. Delete the leading "<" and trailing ">".  Separate message ID
       into local part and domain at the "@".
    3. In both components, transliterate leading dots (".", ASCII 46),
       trailing dots, and dots after the first in sequences of two or
       more consecutive dots, into underscores (ASCII 95).
    4. In both components, transliterate disallowed characters other
       than dots (see the definition of <unquoted-char> in
       Section 5.2) to underscores (ASCII 95).
    5. Form the message ID as
          "<" local-part "@" domain ">"
    NOTE: This algorithm is approximately that of Rich Salz's
    successful gatewaying package.
 Despite the desire to keep message IDs consistent across multiple
 gateways, there is also a more subtle issue that can require a
 different approach.  If the same articles are being gatewayed into
 more than one newsgroup, and it is not possible to arrange that all
 gateways gateway them to the same cross-posted set of newsgroups,
 then the message IDs in the different newsgroups MUST be DIFFERENT.
    NOTE: Otherwise, arrival of an article in one newsgroup will
    prevent it from appearing in another, and which newsgroup a
    particular article appears in will be an accident of which
    direction it arrives from first.  It is very difficult to maintain
    a coherent discussion when each participant sees a randomly

Spencer Historic [Page 87] RFC 1849 Son of 1036 March 2010

    selected 50% of the traffic.  The fundamental problem here is that
    the basic assumption behind message IDs is being violated: the
    gateways are assigning the same message ID to articles that differ
    in an important respect (Newsgroups header).
 In such cases, it is suggested that the newsgroup name, or an agreed-
 on abbreviation thereof, be prepended to the local part of the
 message ID (with a separating ".") by the gateway.  This will ensure
 that multiple gateways generate the same message ID, while also
 ensuring that different newsgroups can be read independently.
    NOTE: It is preferable to have the gateway(s) cross-post the
    article, avoiding the issue altogether, but this may not be
    feasible, especially if one newsgroup is widespread and the other
    is purely local.

10.4. Mail to and from News

 Gatewaying mail to news, and vice versa, is the most obvious form of
 news gatewaying.  It is common to set up gateways between news and
 mail rather too casually.
 It is hard to go very wrong in gatewaying news into a mailing list,
 except for the non-trivial matter of making sure that error reports
 go to the local administration rather than to the authors of news
 articles.  (This requires attention to the "envelope address" as well
 as to the message headers.)  Doing the reverse connection correctly
 is much harder than it looks.
    NOTE: In particular, just feeding the mail message to "inews -h"
    or the equivalent is NOT, repeat NOT, adequate to gateway mail to
    news.  Significant gatewaying software is necessary to do it
    right.  Not all headers of mail messages conform to even the MAIL
    specifications, never mind the stricter rules for news.
 It is useful to distinguish between two different forms of
 mail-to-news gatewaying: gatewaying a mailing list into a newsgroup,
 and operating a "post-by-mail" service in which individual articles
 can be posted to a newsgroup by mailing them to a specific address.
 In the first case, the message is already being "broadcast", and the
 situation can be viewed as gatewaying one form of news into another.
 The second case is closer to that of a moderator posting submissions
 to a moderated newsgroup.
 In either case, the discussions in the preceding two sections are
 relevant, as is the Hippocratic Principle of Section 9.  However,
 some additional considerations are specific to mail-to-news

Spencer Historic [Page 88] RFC 1849 Son of 1036 March 2010

 As mentioned in Section 6, point-to-point headers like To and Cc
 SHOULD NOT appear as such in news, although it is suggested that they
 be transformed to "X-" headers, e.g., X-To and X-Cc, to preserve
 their information content for possible use by readers or
 troubleshooters.  The Received header is entirely specific to MAIL
 and SHOULD be deleted completely during gatewaying, except perhaps
 for the Received header supplied by the gateway host itself.
 The Sender header is a tricky case, one where mailing-list and post-
 by-mail practice should differ.  For gatewaying mailing lists, the
 mailing-list host should be considered a relayer, and the From and
 Sender headers supplied in its transmissions left strictly untouched.
 For post-by-mail, as for a moderator posting a mailed submission, the
 Sender header should reflect the poster rather than the author.  If a
 post-by-mail gateway receives a message with its own Sender header,
 it might wish to preserve the content in an X-Sender header.
 It will generally be necessary to transform between mail's
 In-Reply-To/References convention and news's References/See-Also
 convention, to preserve correct semantics of cross references.  This
 also requires attention when going the other way, from news to mail.
 See the discussion of the difference in Section 6.5.

10.5. Gateway Administration

 Any news system will benefit from an attentive administrator,
 preferably assisted by automated monitoring for anomalies.  This is
 particularly true of gateways.  Gateway software SHOULD be
 instrumented so that unusual occurrences, such as sudden massive
 surges in traffic, are reported promptly.  It is desirable, in fact,
 to go further: gateway software SHOULD endeavor to limit damage in
 the event that the administrator does not respond promptly.
    NOTE: For example, software might limit the gatewaying rate by
    queueing incoming traffic and emptying the queue at a finite
    maximum rate (well below the maximum that the host is capable of!)
    that is set by the administrator and is not raised automatically.
 Traffic gatewayed into a news network SHOULD include a suitable
 header, perhaps X-Gateway-Administrator, giving an electronic address
 that can be used to report problems.  This SHOULD be an address that
 goes directly to a human, and not to a "routine administrative
 issues" mailbox that is examined only occasionally, since the point
 is to be able to reach the administrator quickly in an emergency.
 Gateway administrators SHOULD arrange substitutes to cover gateway
 operation (with suitable redirection of mail) when they are on
 vacation, etc.

Spencer Historic [Page 89] RFC 1849 Son of 1036 March 2010

11. Security and Related Issues

 Although the interchange format itself raises no significant security
 issues, the wider context does.

11.1. Leakage

 The most obvious form of security problem with news is "leakage" of
 articles that are intended to have only restricted circulation.  The
 flooding algorithm is EXTREMELY good at finding any path by which
 articles can leave a subnet with supposedly restrictive boundaries.
 Substantial administrative effort is required to ensure that local
 newsgroups remain local, unless connections to the outside world are
 tightly restricted.
 A related problem is that the sendme control message can be used to
 ask for any article by its message ID.  The usefulness of this has
 declined as message-ID generation algorithms have become less
 predictable, but it remains a potential problem for "secure"
 newsgroups.  Hosts with such newsgroups may wish to disable the
 sendme control message entirely.
 The sendsys, version, and whogets control messages also allow
 "outsiders" to request information from "inside", which may reveal
 details of internal topology (etc.)  that are considered
 confidential.  (Note that at least limited openness about such
 matters may be a condition of membership in such networks, e.g.,
 Organizations wishing to control these forms of leakage are strongly
 advised to designate a small number of "official gateway" hosts to
 handle all news exchange with the outside world, so that a bounded
 amount of administrative effort is needed to control propagation and
 eliminate problems.  Attempts to keep news out entirely, by refusing
 to support an official gateway, typically result in large numbers of
 unofficial partial gateways appearing over time.  Such a
 configuration is much more difficult to troubleshoot.
 A somewhat related problem is the possibility of proprietary material
 being disclosed unintentionally by a poster who does not realize how
 far his words will propagate, either from sheer misunderstanding or
 because of errors made (by human or software) in followup
 preparation.  There is little that can be done about this except

Spencer Historic [Page 90] RFC 1849 Son of 1036 March 2010

11.2. Attacks

 Although the limitations of the medium restrict what can be done to
 attack a host via news, some possibilities exist, most of them
 problems news shares with mail.
 If reading agents are careless about transmitting non-printable
 characters to output devices, malicious posters may post articles
 containing control sequences ("letterbombs") meant to have various
 destructive effects on output devices.  Possible effects depend on
 the device, but they can include hardware damage (e.g., by repeated
 writing of values into configuration memories that can tolerate only
 a limited number of write cycles) and security violation (e.g., by
 reprogramming function keys potentially used by privileged readers).
 A more sophisticated variation on the letterbomb is inclusion of
 "Trojan horses" in programs.  Obviously, readers must be cautious
 about using software found in news, but more subtly, reading agents
 must also exercise care.  MIME messages can include material that is
 executable in some sense, such as PostScript documents (which are
 programs!), and letterbombs may be introduced into such material.
 Given the presence of finite resources and other software
 limitations, some degree of system disruption can be achieved by
 posting otherwise-innocent material in great volume, either in single
 huge articles (see Section 4.6) or in a stream of modest-sized
 articles.  (Some would say that the steady growth of Usenet volume
 constitutes a subtle and unintentional attack of the latter type;
 certainly it can have disruptive effects if administrators are
 inattentive.)  Systems need some ability to cope with surges, because
 single huge articles occur occasionally as the result of software
 error, innocent misunderstanding, or deliberate malice; and downtime
 at upstream hosts can cause droughts, followed by floods, of
 legitimate articles.  (There is also a certain amount of normal
 variation; for example, Usenet traffic is noticeably lighter on
 weekends and during Christmas holidays, and rises noticeably at the
 start of the school term of North American universities.)  However, a
 site that normally receives little traffic may be quite vulnerable to
 "swamping" attack if its software is insufficiently careful.
 In general, careless implementation may open doors that are not
 intrinsic to news.  In particular, implementation of control messages
 (see Sections 6.6 and 7) and unbatchers (see Sections 8.1 and 8.2)
 via a command interpreter requires substantial precautions to ensure
 that only the intended capabilities are available.  Care must also be
 taken that article-supplied text is not fed to programs that have
 escapes to command interpreters.

Spencer Historic [Page 91] RFC 1849 Son of 1036 March 2010

 Finally, there is considerable potential for malice in the sendsys,
 version, and whogets control messages.  They are not harmful to the
 hosts receiving them as news, but they can be used to enlist those
 hosts (by the thousands) as unwitting allies in a mail-swamping
 attack on a victim who may not even receive news.  The precautions
 discussed in Section 7.5 can reduce the potential for such attacks
 considerably, but the hazard cannot be eliminated as long as these
 control messages exist.

11.3. Anarchy

 The highly distributed nature of news propagation, and the lack of
 adequate authentication protocols (especially for use over the less-
 interactive transport mechanisms such as UUCP), make article forgery
 relatively straightforward.  It may be possible to at least track a
 forgery to its source, once it is recognized as such, but clever
 forgers can make even that relatively difficult.  The assumption that
 forgeries will be recognized as such is also not to be taken for
 granted; readers are notoriously prone to blindly assuming
 authenticity.  If a forged article's initial path list includes the
 relayer name of the supposed poster's host, the article will never be
 sent to that host, and the alleged author may learn about the forgery
 secondhand or not at all.
 A particularly noxious form of forgery is the forged "cancel" control
 message.  Notably, it is relatively straightforward to write software
 that will automatically send out a (forged) cancel message for any
 article meeting some criterion, e.g., written by a specific author.
 The authentication problems discussed in Section 7.1 make it
 difficult to solve this without crippling cancel's important
 A related problem is the possibility of disagreements over newsgroup
 creation, on networks where such things are not decided by central
 authorities.  There have been cases of "rmgroup wars", where one
 poster persistently sends out newgroup messages to create a newsgroup
 and another, equally persistently, sends out rmgroup messages asking
 that it be removed.  This is not particularly damaging, if relayers
 are configured to be cautious, but it can cause serious confusion
 among innocent third parties who just want to know whether or not
 they can use the newsgroup for communication.

11.4. Liability

 News shares the legal uncertainty surrounding other forms of
 electronic communication: what rules apply to this new medium of
 information exchange?  News is a particularly problematic case

Spencer Historic [Page 92] RFC 1849 Son of 1036 March 2010

 because it is a broadcast medium rather than a point-to-point one
 like mail, and analogies to older forms of communication are
 particularly weak.
 Are news-carrying hosts common carriers, like the phone companies,
 providing communications paths without having either authority over
 or responsibility for content?  Or are they publishers, responsible
 for the content regardless of whether they are aware of it or not?
 Or something in between?  Such questions are particularly significant
 when the content is technically criminal, e.g., some types of
 sexually oriented material in some jurisdictions, in which case
 ignorance of its presence may not be an adequate defense.
 Even in milder situations such as libel or copyright violation, the
 responsibilities of the poster, his host, and other hosts carrying
 the traffic are unclear.  Note, in particular, the problems arising
 when the article is a forgery, or when the alleged author claims it
 is a forgery but cannot prove this.

12. References

 [ISO/IEC9899]  "Information technology - Programming Language C",
                ISO/IEC 9899:1990 {more recently 9899:1999}, 1990.
 [Metamail]     Borenstein, N.,
                February 1994.
 [RFC821]       Postel, J., "Simple Mail Transfer Protocol", STD 10,
                RFC 821, August 1982.
                TEXT MESSAGES", STD 11, RFC 822, August 1982.
 [RFC850]       Horton, M., "Standard for interchange of Usenet
                messages", RFC 850, June 1983.
 [RFC977]       Kantor, B. and P. Lapsley, "Network News Transfer
                Protocol - A Proposed Standard for the Stream-Based
                Transmission of News", RFC 977, February 1986.
 [RFC1036]      Horton, M. and R. Adams, "Standard for interchange of
                USENET Messages", RFC 1036, December 1987.
 [RFC1123]      Braden, R., Ed., "Requirements for Internet Hosts -
                Application and Support", STD 3, RFC 1123,
                October 1989.

Spencer Historic [Page 93] RFC 1849 Son of 1036 March 2010

 [RFC1341]      Borenstein, N. and N. Freed, "MIME (Multipurpose
                Internet Mail Extensions): Mechanisms for Specifying
                and Describing the Format of Internet Message Bodies",
                RFC 1341, June 1992.
 [RFC1342]      Moore, K., "Representation of Non-ASCII Text in
                Internet Message Headers", RFC 1342, June 1992.
 [RFC1345]      Simonsen, K., "Character Mnemonics and Character
                Sets", RFC 1345, June 1992.
 [RFC1413]      St. Johns, M., "Identification Protocol", RFC 1413,
                February 1993.
 [RFC1456]      Vietnamese Standardization Working Group, "Conventions
                for Encoding the Vietnamese Language", RFC 1456,
                May 1993.
 [RFC1544]      Rose, M., "The Content-MD5 Header Field", RFC 1544,
                November 1993.
 [RFC1896]      Resnick, P. and A. Walker, "The text/enriched MIME
                Content-type", RFC 1896, February 1996.
 [RFC2045]      Freed, N. and N. Borenstein, "Multipurpose Internet
                Mail Extensions (MIME) Part One: Format of Internet
                Message Bodies", RFC 2045, November 1996.
 [RFC2046]      Freed, N. and N. Borenstein, "Multipurpose Internet
                Mail Extensions (MIME) Part Two: Media Types",
                RFC 2046, November 1996.
 [RFC2047]      Moore, K., "MIME (Multipurpose Internet Mail
                Extensions) Part Three: Message Header Extensions for
                Non-ASCII Text", RFC 2047, November 1996.
 [RFC2049]      Freed, N. and N. Borenstein, "Multipurpose Internet
                Mail Extensions (MIME) Part Five: Conformance Criteria
                and Examples", RFC 2049, November 1996.
 [RFC2822]      Resnick, P., Ed., "Internet Message Format", RFC 2822,
                April 2001.
 [RFC3977]      Feather, C., "Network News Transfer Protocol (NNTP)",
                RFC 3977, October 2006.

Spencer Historic [Page 94] RFC 1849 Son of 1036 March 2010

 [RFC5322]      Resnick, P., Ed., "Internet Message Format", RFC 5322,
                October 2008.
 [RFC5536]      Murchison, K., Ed., Lindsey, C., and D. Kohn, "Netnews
                Article Format", RFC 5536, November 2009.
 [RFC5537]      Allbery, R., Ed., and C. Lindsey, "Netnews
                Architecture and Protocols", RFC 5537, November 2009.
 [Sanderson]    David Sanderson, Smileys, O'Reilly & Associates Ltd.,
 [UUCP]         Tim O'Reilly and Grace Todino, Managing UUCP and
                Usenet, O'Reilly & Associates Ltd., January 1992.
 [X3.4]         "American National Standard for Information Systems -
                Coded Character Sets - 7-Bit American National
                Standard Code for Information Interchange (7-Bit
                ASCII)", ANSI X3.4, March 1986.

Spencer Historic [Page 95] RFC 1849 Son of 1036 March 2010

Appendix A. Archaeological Notes

A.1. "A News" Article Format

 The obsolete "A News" article format consisted of exactly five lines
 of header information, followed by the body.  For example:
    Fri Nov 19 16:14:55 1982
    Usenet Etiquette - Please Read
 The first line consisted of an "A" followed by an article ID
 (analogous to a message ID and used for similar purposes).  The
 second line was the list of newsgroups.  The third line was the path.
 The fourth was the date, in the format above (all fields fixed
 width), resembling an Internet date but not quite the same.  The
 fifth was the subject.
 This format is documented for archaeological purposes only.  Do not
 generate articles in this format.

A.2. Early "B News" Article Format

 This obsolete pseudo-Internet article format, used briefly during the
 transition between the A News format and the modern format, followed
 the general outline of a MAIL message but with some non-standard
 headers.  For example:
    From: cbosgd!mhuxj!mhuxt!eagle!jerry (Jerry Schwarz)
    Newsgroups: news.misc
    Title: Usenet Etiquette -- Please Read
    Article-I.D.: eagle.642
    Posted: Fri Nov 19 16:14:55 1982
    Received: Fri Nov 19 16:59:30 1982
    Expires: Mon Jan 1 00:00:00 1990
 The From header contained the information now found in the Path
 header, plus possibly the full name now typically found in the From
 header.  The Title header contained what is now the Subject content.

Spencer Historic [Page 96] RFC 1849 Son of 1036 March 2010

 The Posted header contained what is now the Date content.  The
 Article-I.D. header contained an article ID, analogous to a message
 ID and used for similar purposes.  The Newsgroups and Expires headers
 were approximately as they are now.  The Received header contained
 the date when the latest relayer to process the article first saw it.
 All dates were in the above format, with all fields fixed width,
 resembling an Internet date but not quite the same.
 This format is documented for archaeological purposes only.  Do not
 generate articles in this format.

A.3. Obsolete Headers

 Early versions of news software following the modern format sometimes
 generated headers like the following:
    Relay-Version: version B 2.10 2/13/83; site cbosgd.UUCP
    Posting-Version: version B 2.10 2/13/83; site eagle.UUCP
    Date-Received: Friday, 19-Nov-82 16:59:30 EST
 Relay-Version contained version information about the relayer that
 last processed the article.  Posting-Version contained version
 information about the posting agent that posted the article.  Date-
 Received contained the date when the last relayer to process the
 article first saw it (in a slightly nonstandard format).
 These headers are documented for archaeological purposes only.  Do
 not generate articles using them.

A.4. Obsolete Control Messages

 There once was a senduuname control message, resembling sendsys but
 requesting transmission of the list of hosts to which the receiving
 host had UUCP connections.  This rapidly ceased to be of much use,
 and many organizations consider information about their internal
 connectivity to be confidential.
 Historically, a checkgroups body consisting of one or two lines, the
 first of the form "-n newsgroup", caused checkgroups to apply to only
 that single newsgroup.  This form is documented for archaeological
 purposes only; do not use it.
 Historically, an article posted to a newsgroup whose name had exactly
 three components of which the third was "ctl" signified that article
 was to be taken as a control message.  The Subject header specified
 the actions in the same way the Control header does now.  This form
 is documented for archaeological purposes only; do not use it; do not
 implement it.

Spencer Historic [Page 97] RFC 1849 Son of 1036 March 2010

Appendix B. A Quick Tour of MIME

 (The editor wishes to thank Luc Rooijakkers; most of this appendix is
 a lightly edited version of a summary he kindly supplied.)
 MIME (Multipurpose Internet Mail Extensions) is an upward-compatible
 set of extensions to [RFC822], currently documented in [RFC2045],
 [RFC2046], and [RFC2047].  This appendix summarizes these documents.
 See the MIME RFCs for more information; they are very readable.
    UNRESOLVED ISSUE: These RFC numbers (here and elsewhere in this
    Draft) need updating when the new MIME RFCs come out {now
 MIME defines the following new headers:
 The MIME-Version header is mandatory for all messages conforming to
 the MIME specification and carries the version number of the MIME
 specification.  Example:
    MIME-Version: 1.0
 The Content-Type header indicates the content type of the message.
 Content types are split into a top-level type and a subtype,
 separated by a slash.  Auxiliary information can also be supplied,
 using an attribute-value notation.  Example:
    Content-Type: text/plain; charset=us-ascii
 (In the absence of a Content-Type header this is in fact the default
 content type.)
 Important type/subtype combinations are:
 text/plain              Plain text, possibly in a non-ASCII character
 text/enriched           A very simple wordprocessor-like language
                         supporting character attributes (e.g.,
                         underlining), justification control, and
                         multiple character sets.  (This proposal has

Spencer Historic [Page 98] RFC 1849 Son of 1036 March 2010

                         gone through several iterations and has
                         recently split off from the main MIME RFCs
                         into a separate document [RFC1896].)
 message/rfc822          A mail message conforming to a slightly
                         relaxed version of [RFC822].
 message/partial         Part of a message (supporting the transparent
                         splitting and joining of messages when they
                         are too large to be handled by some transport
 message/external-body   A message whose body is external.  Possible
                         access methods include via mail, FTP, local
                         file, etc.
 multipart/mixed         A message whose body consists of multiple
                         parts, possibly of different types, intended
                         to be viewed in serial order.  Each part
                         looks like an [RFC822] message, consisting of
                         headers and a body.  Most of the [RFC822]
                         headers have no defined semantics for body
 multipart/parallel      Likewise, except that the parts are intended
                         to be viewed in parallel (on user agents that
                         support it).
 multipart/alternative   Likewise, except that the parts are intended
                         to be semantically equivalent such that the
                         part that best matches the capabilities of
                         the environment should be displayed.  For
                         example, a message may include plain-text,
                         enriched-text, and postscript versions of
                         some document.
 multipart/digest        A variant of multipart/mixed especially
                         intended for message digests (the default
                         type of the parts is message/rfc822 instead
                         of text/plain, saving on the number of
                         headers for the parts).
 application/postscript  A PostScript document.  (PostScript is a
                         trademark of Adobe.)
 Other top-level types exist for still images, audio, and video

Spencer Historic [Page 99] RFC 1849 Son of 1036 March 2010

 Some of the above types require the ability to transport binary data.
 Since the existing message systems usually do not support this, MIME
 provides a Content-Transfer-Encoding header to indicate the kind of
 encoding used.  The possible encodings are:
 7bit              No encoding; the data consists of short (less than
                   1000 characters) lines of 7-bit ASCII data,
                   delimited by EOL sequences.  This is the default
 8bit              Like 7bit, except that bytes with the high-order
                   bit set may be present.  Many transmission paths
                   are incapable of carrying messages that use this
 binary            No encoding; any sequence of bytes may be present.
                   Many transmission paths are incapable of carrying
                   messages that use this encoding.
 base64            The data is encoded by representing every group of
                   3 bytes as 4 characters from the alphabet
                   "A-Za-z0-9+/", which was chosen for its high
                   robustness through mail gateways (the alphabet used
                   by uuencode does not survive ASCII-EBCDIC-ASCII
                   translations).  In the final group of 4 characters,
                   "=" is used for those characters not representing
                   data bytes.  Line length is limited, and EOLs in
                   the encoded form are ignored.
 quoted-printable  Any byte can be represented by a three-character
                   "=XX" sequence where the X's are uppercase
                   hexadecimal digits.  Bytes representing printable
                   7-bit US-ASCII characters except "=" may be
                   represented literally.  Tabs and blanks may be
                   represented literally if not at the end of a line.
                   Line length is limited, and an EOL preceded by "="
                   was inserted for this purpose and is not present in
                   the original.
 The base64 and quoted-printable encodings are applied to data in
 Internet canonical form, which means that any EOL encoded as anything
 but EOL must be an Internet canonical EOL: CR followed by LF.
 The Content-Description header allows further description of a body
 part, analogous to the use of Subject for messages.

Spencer Historic [Page 100] RFC 1849 Son of 1036 March 2010

 Finally, the Content-ID header can be used to assign an
 identification to body parts, analogous to the assignment of
 identifications to messages by Message-ID.
 Note that most of these headers are structured header fields, as
 defined in [RFC822].  Consequently, comments are allowed in their
 values.  The following is a legal MIME header:
    Content-Type: (a comment) text (yeah)   /
            plain    (and now some params:) ; charset= (guess what)
       iso-8859-1 (we don't have iso-10646 yet, pity)
    NOTE: Although the MIME specification was developed for mail,
    there is nothing precluding its use for news as well.  While it
    might simplify implementation to restrict the MIME headers
    somewhat, in the same way that other news headers (e.g., From) are
    restricted subsets of the [RFC822] originals, this would add yet
    another divergence between two formats that ought to be as
    compatible as possible.  In the case of the MIME headers, there is
    no body of existing code posing compatibility concerns.  A full-
    featured MIME reading agent needs a full [RFC822] parser anyway,
    to properly handle body parts of types like message/rfc822, so
    there is little gain from restricting MIME headers.  Adopting the
    MIME specification unchanged seems best.  However, article-level
    MIME headers must still comply with the overall news header syntax
    given in Section 4, so that news software that is NOT interested
    in MIME need not contain a full [RFC822] parser.
 "MIME (Multipurpose Internet Mail Extensions) Part Three: Message
 Header Extensions for Non-ASCII Text" [RFC2047] addresses the problem
 of non-ASCII characters in headers.  An example of a header using the
 [RFC2047] mechanism is
    From: =?ISO-8859-1?Q?Andr=E9_?= Pirard <>
 Such encodings are allowed in selected headers, subject to the
 restrictions listed in [RFC2047].
 The MIME effort has also produced an RFC defining a Content-MD5
 header [RFC1544] containing an MD5-based "checksum" of the contents
 of an article or body part, giving high confidence of detecting
 accidental modifications to the contents.
 The "metamail" software package [Metamail] helps provide MIME support
 with minimal changes to mailers and may also be relevant to news
 reading agents.

Spencer Historic [Page 101] RFC 1849 Son of 1036 March 2010

 The PEM (Privacy Enhanced Mail) effort is pursuing analogous
 facilities to offer stronger guarantees against malicious
 modifications, unauthorized eavesdropping, and forgery.  This work
 too may be applicable to news, once it is reconciled with MIME (by
 efforts now underway).

Spencer Historic [Page 102] RFC 1849 Son of 1036 March 2010

Appendix C. Summary of Changes Since RFC 1036

 This Draft is much longer than [RFC1036], so there is obviously much
 change in content.  Much of this is just increased precision and
 rigor.  Noteworthy changes and additions include:
    + restrictions on article bodies (Section 4.3)
    + all references to MIME facilities
    + size limits on articles
    + precise specification of Date-content syntax
    + message IDs must never be re-used, ever
    + "!" is the only Path delimiter
    + multiple moderators in the Approved header
    + rules on References trimming, and the _-_ mechanism
    + generalization of the Xref rules
    + multiple message IDs in Cancel and Supersedes
    + Also-Control
    + See-Also
    + Article-Names
    + Article-Updates
    + more precise rules for cancellation
    + cancellation authorization based on From, not Sender
    + "unmoderated" and descriptors in newgroup messages
    + restrictive rules on handling of sendsys and version messages
    + the whogets control message
    + precise specification of checkgroups messages
    + compression type preferably specified out-of-band

Spencer Historic [Page 103] RFC 1849 Son of 1036 March 2010

    + rules for encapsulating news in MIME mail
    + tighter specification of relayer functioning (Section 9.1)
    + the "newsmaster" contact address
    + rules for gatewaying (Section 10)
    + discussion of security issues (Section 11)

Spencer Historic [Page 104] RFC 1849 Son of 1036 March 2010

Appendix D. Summary of Completely New Features

 Most of this Draft merely documents existing practice, preferred
 versions thereof, or straightforward generalizations of it, but there
 are a few outright inventions.  These are:
    + the _-_ mechanism for References trimming
    + Also-Control
    + See-Also
    + Article-Names
    + Article-Updates
    + the whogets control message

Spencer Historic [Page 105] RFC 1849 Son of 1036 March 2010

Appendix E. Summary of Differences from RFCs 822 and 1123

 The following are noteworthy differences between this Draft's
 articles and MAIL messages:
    + generally less-permissive header syntax
    + notably, limited From syntax
    + MAIL header comments allowed in only a few contexts
    + slightly more restricted message-ID syntax
    + several more mandatory headers
    + duplicate headers forbidden
    + References/See-Also versus In-Reply-To/References (Section 6.5)
    + case sensitivity in some contexts
    + point-to-point headers, e.g., To and Cc, forbidden (Section 6)
    + several new headers

Author's Address

 Henry Spencer
 SP Systems
 Box 280 Stn. A
 Toronto, Ontario M5W1B2

Spencer Historic [Page 106]

/data/webs/external/dokuwiki/data/pages/rfc/rfc1849.txt · Last modified: 2010/03/26 23:22 by

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki