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rfc:rfc2822

Network Working Group P. Resnick, Editor Request for Comments: 2822 QUALCOMM Incorporated Obsoletes: 822 April 2001 Category: Standards Track

                      Internet Message Format

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

 This standard specifies a syntax for text messages that are sent
 between computer users, within the framework of "electronic mail"
 messages.  This standard supersedes the one specified in Request For
 Comments (RFC) 822, "Standard for the Format of ARPA Internet Text
 Messages", updating it to reflect current practice and incorporating
 incremental changes that were specified in other RFCs.

Table of Contents

 1. Introduction ............................................... 3
 1.1. Scope .................................................... 3
 1.2. Notational conventions ................................... 4
 1.2.1. Requirements notation .................................. 4
 1.2.2. Syntactic notation ..................................... 4
 1.3. Structure of this document ............................... 4
 2. Lexical Analysis of Messages ............................... 5
 2.1. General Description ...................................... 5
 2.1.1. Line Length Limits ..................................... 6
 2.2. Header Fields ............................................ 7
 2.2.1. Unstructured Header Field Bodies ....................... 7
 2.2.2. Structured Header Field Bodies ......................... 7
 2.2.3. Long Header Fields ..................................... 7
 2.3. Body ..................................................... 8
 3. Syntax ..................................................... 9
 3.1. Introduction ............................................. 9
 3.2. Lexical Tokens ........................................... 9

Resnick Standards Track [Page 1] RFC 2822 Internet Message Format April 2001

 3.2.1. Primitive Tokens ....................................... 9
 3.2.2. Quoted characters ......................................10
 3.2.3. Folding white space and comments .......................11
 3.2.4. Atom ...................................................12
 3.2.5. Quoted strings .........................................13
 3.2.6. Miscellaneous tokens ...................................13
 3.3. Date and Time Specification ..............................14
 3.4. Address Specification ....................................15
 3.4.1. Addr-spec specification ................................16
 3.5 Overall message syntax ....................................17
 3.6. Field definitions ........................................18
 3.6.1. The origination date field .............................20
 3.6.2. Originator fields ......................................21
 3.6.3. Destination address fields .............................22
 3.6.4. Identification fields ..................................23
 3.6.5. Informational fields ...................................26
 3.6.6. Resent fields ..........................................26
 3.6.7. Trace fields ...........................................28
 3.6.8. Optional fields ........................................29
 4. Obsolete Syntax ............................................29
 4.1. Miscellaneous obsolete tokens ............................30
 4.2. Obsolete folding white space .............................31
 4.3. Obsolete Date and Time ...................................31
 4.4. Obsolete Addressing ......................................33
 4.5. Obsolete header fields ...................................33
 4.5.1. Obsolete origination date field ........................34
 4.5.2. Obsolete originator fields .............................34
 4.5.3. Obsolete destination address fields ....................34
 4.5.4. Obsolete identification fields .........................35
 4.5.5. Obsolete informational fields ..........................35
 4.5.6. Obsolete resent fields .................................35
 4.5.7. Obsolete trace fields ..................................36
 4.5.8. Obsolete optional fields ...............................36
 5. Security Considerations ....................................36
 6. Bibliography ...............................................37
 7. Editor's Address ...........................................38
 8. Acknowledgements ...........................................39
 Appendix A. Example messages ..................................41
 A.1. Addressing examples ......................................41
 A.1.1. A message from one person to another with simple
        addressing .............................................41
 A.1.2. Different types of mailboxes ...........................42
 A.1.3. Group addresses ........................................43
 A.2. Reply messages ...........................................43
 A.3. Resent messages ..........................................44
 A.4. Messages with trace fields ...............................46
 A.5. White space, comments, and other oddities ................47
 A.6. Obsoleted forms ..........................................47

Resnick Standards Track [Page 2] RFC 2822 Internet Message Format April 2001

 A.6.1. Obsolete addressing ....................................48
 A.6.2. Obsolete dates .........................................48
 A.6.3. Obsolete white space and comments ......................48
 Appendix B. Differences from earlier standards ................49
 Appendix C. Notices ...........................................50
 Full Copyright Statement ......................................51

1. Introduction

1.1. Scope

 This standard specifies a syntax for text messages that are sent
 between computer users, within the framework of "electronic mail"
 messages.  This standard supersedes the one specified in Request For
 Comments (RFC) 822, "Standard for the Format of ARPA Internet Text
 Messages" [RFC822], updating it to reflect current practice and
 incorporating incremental changes that were specified in other RFCs
 [STD3].
 This standard specifies a syntax only for text messages.  In
 particular, it makes no provision for the transmission of images,
 audio, or other sorts of structured data in electronic mail messages.
 There are several extensions published, such as the MIME document
 series [RFC2045, RFC2046, RFC2049], which describe mechanisms for the
 transmission of such data through electronic mail, either by
 extending the syntax provided here or by structuring such messages to
 conform to this syntax.  Those mechanisms are outside of the scope of
 this standard.
 In the context of electronic mail, messages are viewed as having an
 envelope and contents.  The envelope contains whatever information is
 needed to accomplish transmission and delivery.  (See [RFC2821] for a
 discussion of the envelope.)  The contents comprise the object to be
 delivered to the recipient.  This standard applies only to the format
 and some of the semantics of message contents.  It contains no
 specification of the information in the envelope.
 However, some message systems may use information from the contents
 to create the envelope.  It is intended that this standard facilitate
 the acquisition of such information by programs.
 This specification is intended as a definition of what message
 content format is to be passed between systems.  Though some message
 systems locally store messages in this format (which eliminates the
 need for translation between formats) and others use formats that
 differ from the one specified in this standard, local storage is
 outside of the scope of this standard.

Resnick Standards Track [Page 3] RFC 2822 Internet Message Format April 2001

 Note: This standard is not intended to dictate the internal formats
 used by sites, the specific message system features that they are
 expected to support, or any of the characteristics of user interface
 programs that create or read messages.  In addition, this standard
 does not specify an encoding of the characters for either transport
 or storage; that is, it does not specify the number of bits used or
 how those bits are specifically transferred over the wire or stored
 on disk.

1.2. Notational conventions

1.2.1. Requirements notation

 This document occasionally uses terms that appear in capital letters.
 When the terms "MUST", "SHOULD", "RECOMMENDED", "MUST NOT", "SHOULD
 NOT", and "MAY" appear capitalized, they are being used to indicate
 particular requirements of this specification.  A discussion of the
 meanings of these terms appears in [RFC2119].

1.2.2. Syntactic notation

 This standard uses the Augmented Backus-Naur Form (ABNF) notation
 specified in [RFC2234] for the formal definitions of the syntax of
 messages.  Characters will be specified either by a decimal value
 (e.g., the value %d65 for uppercase A and %d97 for lowercase A) or by
 a case-insensitive literal value enclosed in quotation marks (e.g.,
 "A" for either uppercase or lowercase A).  See [RFC2234] for the full
 description of the notation.

1.3. Structure of this document

 This document is divided into several sections.
 This section, section 1, is a short introduction to the document.
 Section 2 lays out the general description of a message and its
 constituent parts.  This is an overview to help the reader understand
 some of the general principles used in the later portions of this
 document.  Any examples in this section MUST NOT be taken as
 specification of the formal syntax of any part of a message.
 Section 3 specifies formal ABNF rules for the structure of each part
 of a message (the syntax) and describes the relationship between
 those parts and their meaning in the context of a message (the
 semantics).  That is, it describes the actual rules for the structure
 of each part of a message (the syntax) as well as a description of
 the parts and instructions on how they ought to be interpreted (the
 semantics).  This includes analysis of the syntax and semantics of

Resnick Standards Track [Page 4] RFC 2822 Internet Message Format April 2001

 subparts of messages that have specific structure.  The syntax
 included in section 3 represents messages as they MUST be created.
 There are also notes in section 3 to indicate if any of the options
 specified in the syntax SHOULD be used over any of the others.
 Both sections 2 and 3 describe messages that are legal to generate
 for purposes of this standard.
 Section 4 of this document specifies an "obsolete" syntax.  There are
 references in section 3 to these obsolete syntactic elements.  The
 rules of the obsolete syntax are elements that have appeared in
 earlier revisions of this standard or have previously been widely
 used in Internet messages.  As such, these elements MUST be
 interpreted by parsers of messages in order to be conformant to this
 standard.  However, since items in this syntax have been determined
 to be non-interoperable or to cause significant problems for
 recipients of messages, they MUST NOT be generated by creators of
 conformant messages.
 Section 5 details security considerations to take into account when
 implementing this standard.
 Section 6 is a bibliography of references in this document.
 Section 7 contains the editor's address.
 Section 8 contains acknowledgements.
 Appendix A lists examples of different sorts of messages.  These
 examples are not exhaustive of the types of messages that appear on
 the Internet, but give a broad overview of certain syntactic forms.
 Appendix B lists the differences between this standard and earlier
 standards for Internet messages.
 Appendix C has copyright and intellectual property notices.

2. Lexical Analysis of Messages

2.1. General Description

 At the most basic level, a message is a series of characters.  A
 message that is conformant with this standard is comprised of
 characters with values in the range 1 through 127 and interpreted as
 US-ASCII characters [ASCII].  For brevity, this document sometimes
 refers to this range of characters as simply "US-ASCII characters".

Resnick Standards Track [Page 5] RFC 2822 Internet Message Format April 2001

 Note: This standard specifies that messages are made up of characters
 in the US-ASCII range of 1 through 127.  There are other documents,
 specifically the MIME document series [RFC2045, RFC2046, RFC2047,
 RFC2048, RFC2049], that extend this standard to allow for values
 outside of that range.  Discussion of those mechanisms is not within
 the scope of this standard.
 Messages are divided into lines of characters.  A line is a series of
 characters that is delimited with the two characters carriage-return
 and line-feed; that is, the carriage return (CR) character (ASCII
 value 13) followed immediately by the line feed (LF) character (ASCII
 value 10).  (The carriage-return/line-feed pair is usually written in
 this document as "CRLF".)
 A message consists of header fields (collectively called "the header
 of the message") followed, optionally, by a body.  The header is a
 sequence of lines of characters with special syntax as defined in
 this standard. The body is simply a sequence of characters that
 follows the header and is separated from the header by an empty line
 (i.e., a line with nothing preceding the CRLF).

2.1.1. Line Length Limits

 There are two limits that this standard places on the number of
 characters in a line. Each line of characters MUST be no more than
 998 characters, and SHOULD be no more than 78 characters, excluding
 the CRLF.
 The 998 character limit is due to limitations in many implementations
 which send, receive, or store Internet Message Format messages that
 simply cannot handle more than 998 characters on a line. Receiving
 implementations would do well to handle an arbitrarily large number
 of characters in a line for robustness sake. However, there are so
 many implementations which (in compliance with the transport
 requirements of [RFC2821]) do not accept messages containing more
 than 1000 character including the CR and LF per line, it is important
 for implementations not to create such messages.
 The more conservative 78 character recommendation is to accommodate
 the many implementations of user interfaces that display these
 messages which may truncate, or disastrously wrap, the display of
 more than 78 characters per line, in spite of the fact that such
 implementations are non-conformant to the intent of this
 specification (and that of [RFC2821] if they actually cause
 information to be lost). Again, even though this limitation is put on
 messages, it is encumbant upon implementations which display messages

Resnick Standards Track [Page 6] RFC 2822 Internet Message Format April 2001

 to handle an arbitrarily large number of characters in a line
 (certainly at least up to the 998 character limit) for the sake of
 robustness.

2.2. Header Fields

 Header fields are lines composed of a field name, followed by a colon
 (":"), followed by a field body, and terminated by CRLF.  A field
 name MUST be composed of printable US-ASCII characters (i.e.,
 characters that have values between 33 and 126, inclusive), except
 colon.  A field body may be composed of any US-ASCII characters,
 except for CR and LF.  However, a field body may contain CRLF when
 used in header "folding" and  "unfolding" as described in section
 2.2.3.  All field bodies MUST conform to the syntax described in
 sections 3 and 4 of this standard.

2.2.1. Unstructured Header Field Bodies

 Some field bodies in this standard are defined simply as
 "unstructured" (which is specified below as any US-ASCII characters,
 except for CR and LF) with no further restrictions.  These are
 referred to as unstructured field bodies.  Semantically, unstructured
 field bodies are simply to be treated as a single line of characters
 with no further processing (except for header "folding" and
 "unfolding" as described in section 2.2.3).

2.2.2. Structured Header Field Bodies

 Some field bodies in this standard have specific syntactical
 structure more restrictive than the unstructured field bodies
 described above. These are referred to as "structured" field bodies.
 Structured field bodies are sequences of specific lexical tokens as
 described in sections 3 and 4 of this standard.  Many of these tokens
 are allowed (according to their syntax) to be introduced or end with
 comments (as described in section 3.2.3) as well as the space (SP,
 ASCII value 32) and horizontal tab (HTAB, ASCII value 9) characters
 (together known as the white space characters, WSP), and those WSP
 characters are subject to header "folding" and "unfolding" as
 described in section 2.2.3.  Semantic analysis of structured field
 bodies is given along with their syntax.

2.2.3. Long Header Fields

 Each header field is logically a single line of characters comprising
 the field name, the colon, and the field body.  For convenience
 however, and to deal with the 998/78 character limitations per line,
 the field body portion of a header field can be split into a multiple
 line representation; this is called "folding".  The general rule is

Resnick Standards Track [Page 7] RFC 2822 Internet Message Format April 2001

 that wherever this standard allows for folding white space (not
 simply WSP characters), a CRLF may be inserted before any WSP.  For
 example, the header field:
         Subject: This is a test
 can be represented as:
         Subject: This
          is a test
 Note: Though structured field bodies are defined in such a way that
 folding can take place between many of the lexical tokens (and even
 within some of the lexical tokens), folding SHOULD be limited to
 placing the CRLF at higher-level syntactic breaks.  For instance, if
 a field body is defined as comma-separated values, it is recommended
 that folding occur after the comma separating the structured items in
 preference to other places where the field could be folded, even if
 it is allowed elsewhere.
 The process of moving from this folded multiple-line representation
 of a header field to its single line representation is called
 "unfolding". Unfolding is accomplished by simply removing any CRLF
 that is immediately followed by WSP.  Each header field should be
 treated in its unfolded form for further syntactic and semantic
 evaluation.

2.3. Body

 The body of a message is simply lines of US-ASCII characters.  The
 only two limitations on the body are as follows:
  1. CR and LF MUST only occur together as CRLF; they MUST NOT appear

independently in the body.

  1. Lines of characters in the body MUST be limited to 998 characters,

and SHOULD be limited to 78 characters, excluding the CRLF.

 Note: As was stated earlier, there are other standards documents,
 specifically the MIME documents [RFC2045, RFC2046, RFC2048, RFC2049]
 that extend this standard to allow for different sorts of message
 bodies.  Again, these mechanisms are beyond the scope of this
 document.

Resnick Standards Track [Page 8] RFC 2822 Internet Message Format April 2001

3. Syntax

3.1. Introduction

 The syntax as given in this section defines the legal syntax of
 Internet messages.  Messages that are conformant to this standard
 MUST conform to the syntax in this section.  If there are options in
 this section where one option SHOULD be generated, that is indicated
 either in the prose or in a comment next to the syntax.
 For the defined expressions, a short description of the syntax and
 use is given, followed by the syntax in ABNF, followed by a semantic
 analysis.  Primitive tokens that are used but otherwise unspecified
 come from [RFC2234].
 In some of the definitions, there will be nonterminals whose names
 start with "obs-".  These "obs-" elements refer to tokens defined in
 the obsolete syntax in section 4.  In all cases, these productions
 are to be ignored for the purposes of generating legal Internet
 messages and MUST NOT be used as part of such a message.  However,
 when interpreting messages, these tokens MUST be honored as part of
 the legal syntax.  In this sense, section 3 defines a grammar for
 generation of messages, with "obs-" elements that are to be ignored,
 while section 4 adds grammar for interpretation of messages.

3.2. Lexical Tokens

 The following rules are used to define an underlying lexical
 analyzer, which feeds tokens to the higher-level parsers.  This
 section defines the tokens used in structured header field bodies.
 Note: Readers of this standard need to pay special attention to how
 these lexical tokens are used in both the lower-level and
 higher-level syntax later in the document.  Particularly, the white
 space tokens and the comment tokens defined in section 3.2.3 get used
 in the lower-level tokens defined here, and those lower-level tokens
 are in turn used as parts of the higher-level tokens defined later.
 Therefore, the white space and comments may be allowed in the
 higher-level tokens even though they may not explicitly appear in a
 particular definition.

3.2.1. Primitive Tokens

 The following are primitive tokens referred to elsewhere in this
 standard, but not otherwise defined in [RFC2234].  Some of them will
 not appear anywhere else in the syntax, but they are convenient to
 refer to in other parts of this document.

Resnick Standards Track [Page 9] RFC 2822 Internet Message Format April 2001

 Note: The "specials" below are just such an example.  Though the
 specials token does not appear anywhere else in this standard, it is
 useful for implementers who use tools that lexically analyze
 messages.  Each of the characters in specials can be used to indicate
 a tokenization point in lexical analysis.

NO-WS-CTL = %d1-8 / ; US-ASCII control characters

                      %d11 /          ;  that do not include the
                      %d12 /          ;  carriage return, line feed,
                      %d14-31 /       ;  and white space characters
                      %d127

text = %d1-9 / ; Characters excluding CR and LF

                      %d11 /
                      %d12 /
                      %d14-127 /
                      obs-text

specials = "(" / ")" / ; Special characters used in

                      "<" / ">" /     ;  other parts of the syntax
                      "[" / "]" /
                      ":" / ";" /
                      "@" / "\" /
                      "," / "." /
                      DQUOTE
 No special semantics are attached to these tokens.  They are simply
 single characters.

3.2.2. Quoted characters

 Some characters are reserved for special interpretation, such as
 delimiting lexical tokens.  To permit use of these characters as
 uninterpreted data, a quoting mechanism is provided.

quoted-pair = ("\" text) / obs-qp

 Where any quoted-pair appears, it is to be interpreted as the text
 character alone.  That is to say, the "\" character that appears as
 part of a quoted-pair is semantically "invisible".
 Note: The "\" character may appear in a message where it is not part
 of a quoted-pair.  A "\" character that does not appear in a
 quoted-pair is not semantically invisible.  The only places in this
 standard where quoted-pair currently appears are ccontent, qcontent,
 dcontent, no-fold-quote, and no-fold-literal.

Resnick Standards Track [Page 10] RFC 2822 Internet Message Format April 2001

3.2.3. Folding white space and comments

 White space characters, including white space used in folding
 (described in section 2.2.3), may appear between many elements in
 header field bodies.  Also, strings of characters that are treated as
 comments may be included in structured field bodies as characters
 enclosed in parentheses.  The following defines the folding white
 space (FWS) and comment constructs.
 Strings of characters enclosed in parentheses are considered comments
 so long as they do not appear within a "quoted-string", as defined in
 section 3.2.5.  Comments may nest.
 There are several places in this standard where comments and FWS may
 be freely inserted.  To accommodate that syntax, an additional token
 for "CFWS" is defined for places where comments and/or FWS can occur.
 However, where CFWS occurs in this standard, it MUST NOT be inserted
 in such a way that any line of a folded header field is made up
 entirely of WSP characters and nothing else.

FWS = ([*WSP CRLF] 1*WSP) / ; Folding white space

                      obs-FWS

ctext = NO-WS-CTL / ; Non white space controls

                      %d33-39 /       ; The rest of the US-ASCII
                      %d42-91 /       ;  characters not including "(",
                      %d93-126        ;  ")", or "\"

ccontent = ctext / quoted-pair / comment

comment = "(" *([FWS] ccontent) [FWS] ")"

CFWS = *([FWS] comment) 1) / obs-mbox-list

address-list = (address *("," address)) / obs-addr-list

 A mailbox receives mail.  It is a conceptual entity which does not
 necessarily pertain to file storage.  For example, some sites may
 choose to print mail on a printer and deliver the output to the
 addressee's desk.  Normally, a mailbox is comprised of two parts: (1)
 an optional display name that indicates the name of the recipient
 (which could be a person or a system) that could be displayed to the
 user of a mail application, and (2) an addr-spec address enclosed in
 angle brackets ("<" and ">").  There is also an alternate simple form
 of a mailbox where the addr-spec address appears alone, without the
 recipient's name or the angle brackets.  The Internet addr-spec
 address is described in section 3.4.1.
 Note: Some legacy implementations used the simple form where the
 addr-spec appears without the angle brackets, but included the name
 of the recipient in parentheses as a comment following the addr-spec.
 Since the meaning of the information in a comment is unspecified,
 implementations SHOULD use the full name-addr form of the mailbox,
 instead of the legacy form, to specify the display name associated
 with a mailbox.  Also, because some legacy implementations interpret
 the comment, comments generally SHOULD NOT be used in address fields
 to avoid confusing such implementations.
 When it is desirable to treat several mailboxes as a single unit
 (i.e., in a distribution list), the group construct can be used.  The
 group construct allows the sender to indicate a named group of
 recipients. This is done by giving a display name for the group,
 followed by a colon, followed by a comma separated list of any number
 of mailboxes (including zero and one), and ending with a semicolon.
 Because the list of mailboxes can be empty, using the group construct
 is also a simple way to communicate to recipients that the message
 was sent to one or more named sets of recipients, without actually
 providing the individual mailbox address for each of those
 recipients.

3.4.1. Addr-spec specification

 An addr-spec is a specific Internet identifier that contains a
 locally interpreted string followed by the at-sign character ("@",
 ASCII value 64) followed by an Internet domain.  The locally
 interpreted string is either a quoted-string or a dot-atom.  If the
 string can be represented as a dot-atom (that is, it contains no
 characters other than atext characters or "." surrounded by atext

Resnick Standards Track [Page 16] RFC 2822 Internet Message Format April 2001

 characters), then the dot-atom form SHOULD be used and the
 quoted-string form SHOULD NOT be used. Comments and folding white
 space SHOULD NOT be used around the "@" in the addr-spec.

addr-spec = local-part "@" domain

local-part = dot-atom / quoted-string / obs-local-part

domain = dot-atom / domain-literal / obs-domain

domain-literal = [CFWS] "[" *([FWS] dcontent) [FWS] "]" [CFWS]

dcontent = dtext / quoted-pair

dtext = NO-WS-CTL / ; Non white space controls

                      %d33-90 /       ; The rest of the US-ASCII
                      %d94-126        ;  characters not including "[",
                                      ;  "]", or "\"
 The domain portion identifies the point to which the mail is
 delivered. In the dot-atom form, this is interpreted as an Internet
 domain name (either a host name or a mail exchanger name) as
 described in [STD3, STD13, STD14].  In the domain-literal form, the
 domain is interpreted as the literal Internet address of the
 particular host.  In both cases, how addressing is used and how
 messages are transported to a particular host is covered in the mail
 transport document [RFC2821].  These mechanisms are outside of the
 scope of this document.
 The local-part portion is a domain dependent string.  In addresses,
 it is simply interpreted on the particular host as a name of a
 particular mailbox.

3.5 Overall message syntax

 A message consists of header fields, optionally followed by a message
 body.  Lines in a message MUST be a maximum of 998 characters
 excluding the CRLF, but it is RECOMMENDED that lines be limited to 78
 characters excluding the CRLF.  (See section 2.1.1 for explanation.)
 In a message body, though all of the characters listed in the text
 rule MAY be used, the use of US-ASCII control characters (values 1
 through 8, 11, 12, and 14 through 31) is discouraged since their
 interpretation by receivers for display is not guaranteed.

Resnick Standards Track [Page 17] RFC 2822 Internet Message Format April 2001

message = (fields / obs-fields)

                      [CRLF body]

body = *(*998text CRLF) *998text

 The header fields carry most of the semantic information and are
 defined in section 3.6.  The body is simply a series of lines of text
 which are uninterpreted for the purposes of this standard.

3.6. Field definitions

 The header fields of a message are defined here.  All header fields
 have the same general syntactic structure: A field name, followed by
 a colon, followed by the field body.  The specific syntax for each
 header field is defined in the subsequent sections.
 Note: In the ABNF syntax for each field in subsequent sections, each
 field name is followed by the required colon.  However, for brevity
 sometimes the colon is not referred to in the textual description of
 the syntax.  It is, nonetheless, required.
 It is important to note that the header fields are not guaranteed to
 be in a particular order.  They may appear in any order, and they
 have been known to be reordered occasionally when transported over
 the Internet.  However, for the purposes of this standard, header
 fields SHOULD NOT be reordered when a message is transported or
 transformed.  More importantly, the trace header fields and resent
 header fields MUST NOT be reordered, and SHOULD be kept in blocks
 prepended to the message.  See sections 3.6.6 and 3.6.7 for more
 information.
 The only required header fields are the origination date field and
 the originator address field(s).  All other header fields are
 syntactically optional.  More information is contained in the table
 following this definition.

fields = *(trace

  • (resent-date /

resent-from /

                         resent-sender /
                         resent-to /
                         resent-cc /
                         resent-bcc /
                         resent-msg-id))
                      *(orig-date /
                      from /
                      sender /
                      reply-to /

Resnick Standards Track [Page 18] RFC 2822 Internet Message Format April 2001

                      to /
                      cc /
                      bcc /
                      message-id /
                      in-reply-to /
                      references /
                      subject /
                      comments /
                      keywords /
                      optional-field)
 The following table indicates limits on the number of times each
 field may occur in a message header as well as any special
 limitations on the use of those fields.  An asterisk next to a value
 in the minimum or maximum column indicates that a special restriction
 appears in the Notes column.

Field Min number Max number Notes

trace 0 unlimited Block prepended - see

                                              3.6.7

resent-date 0* unlimited* One per block, required

                                              if other resent fields
                                              present - see 3.6.6

resent-from 0 unlimited* One per block - see

                                              3.6.6

resent-sender 0* unlimited* One per block, MUST

                                              occur with multi-address
                                              resent-from - see 3.6.6

resent-to 0 unlimited* One per block - see

                                              3.6.6

resent-cc 0 unlimited* One per block - see

                                              3.6.6

resent-bcc 0 unlimited* One per block - see

                                              3.6.6

resent-msg-id 0 unlimited* One per block - see

                                              3.6.6

orig-date 1 1

from 1 1 See sender and 3.6.2

Resnick Standards Track [Page 19] RFC 2822 Internet Message Format April 2001

sender 0* 1 MUST occur with multi-

                                              address from - see 3.6.2

reply-to 0 1

to 0 1

cc 0 1

bcc 0 1

message-id 0* 1 SHOULD be present - see

                                              3.6.4

in-reply-to 0* 1 SHOULD occur in some

                                              replies - see 3.6.4

references 0* 1 SHOULD occur in some

                                              replies - see 3.6.4

subject 0 1

comments 0 unlimited

keywords 0 unlimited

optional-field 0 unlimited

 The exact interpretation of each field is described in subsequent
 sections.

3.6.1. The origination date field

 The origination date field consists of the field name "Date" followed
 by a date-time specification.

orig-date = "Date:" date-time CRLF

 The origination date specifies the date and time at which the creator
 of the message indicated that the message was complete and ready to
 enter the mail delivery system.  For instance, this might be the time
 that a user pushes the "send" or "submit" button in an application
 program.  In any case, it is specifically not intended to convey the
 time that the message is actually transported, but rather the time at
 which the human or other creator of the message has put the message
 into its final form, ready for transport.  (For example, a portable
 computer user who is not connected to a network might queue a message

Resnick Standards Track [Page 20] RFC 2822 Internet Message Format April 2001

 for delivery.  The origination date is intended to contain the date
 and time that the user queued the message, not the time when the user
 connected to the network to send the message.)

3.6.2. Originator fields

 The originator fields of a message consist of the from field, the
 sender field (when applicable), and optionally the reply-to field.
 The from field consists of the field name "From" and a
 comma-separated list of one or more mailbox specifications.  If the
 from field contains more than one mailbox specification in the
 mailbox-list, then the sender field, containing the field name
 "Sender" and a single mailbox specification, MUST appear in the
 message.  In either case, an optional reply-to field MAY also be
 included, which contains the field name "Reply-To" and a
 comma-separated list of one or more addresses.

from = "From:" mailbox-list CRLF

sender = "Sender:" mailbox CRLF

reply-to = "Reply-To:" address-list CRLF

 The originator fields indicate the mailbox(es) of the source of the
 message.  The "From:" field specifies the author(s) of the message,
 that is, the mailbox(es) of the person(s) or system(s) responsible
 for the writing of the message.  The "Sender:" field specifies the
 mailbox of the agent responsible for the actual transmission of the
 message.  For example, if a secretary were to send a message for
 another person, the mailbox of the secretary would appear in the
 "Sender:" field and the mailbox of the actual author would appear in
 the "From:" field.  If the originator of the message can be indicated
 by a single mailbox and the author and transmitter are identical, the
 "Sender:" field SHOULD NOT be used.  Otherwise, both fields SHOULD
 appear.
 The originator fields also provide the information required when
 replying to a message.  When the "Reply-To:" field is present, it
 indicates the mailbox(es) to which the author of the message suggests
 that replies be sent.  In the absence of the "Reply-To:" field,
 replies SHOULD by default be sent to the mailbox(es) specified in the
 "From:" field unless otherwise specified by the person composing the
 reply.
 In all cases, the "From:" field SHOULD NOT contain any mailbox that
 does not belong to the author(s) of the message.  See also section
 3.6.3 for more information on forming the destination addresses for a
 reply.

Resnick Standards Track [Page 21] RFC 2822 Internet Message Format April 2001

3.6.3. Destination address fields

 The destination fields of a message consist of three possible fields,
 each of the same form: The field name, which is either "To", "Cc", or
 "Bcc", followed by a comma-separated list of one or more addresses
 (either mailbox or group syntax).

to = "To:" address-list CRLF

cc = "Cc:" address-list CRLF

bcc = "Bcc:" (address-list / [CFWS]) CRLF

 The destination fields specify the recipients of the message.  Each
 destination field may have one or more addresses, and each of the
 addresses indicate the intended recipients of the message.  The only
 difference between the three fields is how each is used.
 The "To:" field contains the address(es) of the primary recipient(s)
 of the message.
 The "Cc:" field (where the "Cc" means "Carbon Copy" in the sense of
 making a copy on a typewriter using carbon paper) contains the
 addresses of others who are to receive the message, though the
 content of the message may not be directed at them.
 The "Bcc:" field (where the "Bcc" means "Blind Carbon Copy") contains
 addresses of recipients of the message whose addresses are not to be
 revealed to other recipients of the message.  There are three ways in
 which the "Bcc:" field is used.  In the first case, when a message
 containing a "Bcc:" field is prepared to be sent, the "Bcc:" line is
 removed even though all of the recipients (including those specified
 in the "Bcc:" field) are sent a copy of the message.  In the second
 case, recipients specified in the "To:" and "Cc:" lines each are sent
 a copy of the message with the "Bcc:" line removed as above, but the
 recipients on the "Bcc:" line get a separate copy of the message
 containing a "Bcc:" line.  (When there are multiple recipient
 addresses in the "Bcc:" field, some implementations actually send a
 separate copy of the message to each recipient with a "Bcc:"
 containing only the address of that particular recipient.) Finally,
 since a "Bcc:" field may contain no addresses, a "Bcc:" field can be
 sent without any addresses indicating to the recipients that blind
 copies were sent to someone.  Which method to use with "Bcc:" fields
 is implementation dependent, but refer to the "Security
 Considerations" section of this document for a discussion of each.

Resnick Standards Track [Page 22] RFC 2822 Internet Message Format April 2001

 When a message is a reply to another message, the mailboxes of the
 authors of the original message (the mailboxes in the "From:" field)
 or mailboxes specified in the "Reply-To:" field (if it exists) MAY
 appear in the "To:" field of the reply since these would normally be
 the primary recipients of the reply.  If a reply is sent to a message
 that has destination fields, it is often desirable to send a copy of
 the reply to all of the recipients of the message, in addition to the
 author.  When such a reply is formed, addresses in the "To:" and
 "Cc:" fields of the original message MAY appear in the "Cc:" field of
 the reply, since these are normally secondary recipients of the
 reply.  If a "Bcc:" field is present in the original message,
 addresses in that field MAY appear in the "Bcc:" field of the reply,
 but SHOULD NOT appear in the "To:" or "Cc:" fields.
 Note: Some mail applications have automatic reply commands that
 include the destination addresses of the original message in the
 destination addresses of the reply.  How those reply commands behave
 is implementation dependent and is beyond the scope of this document.
 In particular, whether or not to include the original destination
 addresses when the original message had a "Reply-To:" field is not
 addressed here.

3.6.4. Identification fields

 Though optional, every message SHOULD have a "Message-ID:" field.
 Furthermore, reply messages SHOULD have "In-Reply-To:" and
 "References:" fields as appropriate, as described below.
 The "Message-ID:" field contains a single unique message identifier.
 The "References:" and "In-Reply-To:" field each contain one or more
 unique message identifiers, optionally separated by CFWS.
 The message identifier (msg-id) is similar in syntax to an angle-addr
 construct without the internal CFWS.

message-id = "Message-ID:" msg-id CRLF

in-reply-to = "In-Reply-To:" 1*msg-id CRLF

references = "References:" 1*msg-id CRLF

msg-id = [CFWS] "<" id-left "@" id-right ">" [CFWS]

id-left = dot-atom-text / no-fold-quote / obs-id-left

id-right = dot-atom-text / no-fold-literal / obs-id-right

no-fold-quote = DQUOTE *(qtext / quoted-pair) DQUOTE

Resnick Standards Track [Page 23] RFC 2822 Internet Message Format April 2001

no-fold-literal = "[" *(dtext / quoted-pair) "]"

 The "Message-ID:" field provides a unique message identifier that
 refers to a particular version of a particular message.  The
 uniqueness of the message identifier is guaranteed by the host that
 generates it (see below).  This message identifier is intended to be
 machine readable and not necessarily meaningful to humans.  A message
 identifier pertains to exactly one instantiation of a particular
 message; subsequent revisions to the message each receive new message
 identifiers.
 Note: There are many instances when messages are "changed", but those
 changes do not constitute a new instantiation of that message, and
 therefore the message would not get a new message identifier.  For
 example, when messages are introduced into the transport system, they
 are often prepended with additional header fields such as trace
 fields (described in section 3.6.7) and resent fields (described in
 section 3.6.6).  The addition of such header fields does not change
 the identity of the message and therefore the original "Message-ID:"
 field is retained.  In all cases, it is the meaning that the sender
 of the message wishes to convey (i.e., whether this is the same
 message or a different message) that determines whether or not the
 "Message-ID:" field changes, not any particular syntactic difference
 that appears (or does not appear) in the message.
 The "In-Reply-To:" and "References:" fields are used when creating a
 reply to a message.  They hold the message identifier of the original
 message and the message identifiers of other messages (for example,
 in the case of a reply to a message which was itself a reply).  The
 "In-Reply-To:" field may be used to identify the message (or
 messages) to which the new message is a reply, while the
 "References:" field may be used to identify a "thread" of
 conversation.
 When creating a reply to a message, the "In-Reply-To:" and
 "References:" fields of the resultant message are constructed as
 follows:
 The "In-Reply-To:" field will contain the contents of the "Message-
 ID:" field of the message to which this one is a reply (the "parent
 message").  If there is more than one parent message, then the "In-
 Reply-To:" field will contain the contents of all of the parents'
 "Message-ID:" fields.  If there is no "Message-ID:" field in any of
 the parent messages, then the new message will have no "In-Reply-To:"
 field.

Resnick Standards Track [Page 24] RFC 2822 Internet Message Format April 2001

 The "References:" field will contain the contents of the parent's
 "References:" field (if any) followed by the contents of the parent's
 "Message-ID:" field (if any).  If the parent message does not contain
 a "References:" field but does have an "In-Reply-To:" field
 containing a single message identifier, then the "References:" field
 will contain the contents of the parent's "In-Reply-To:" field
 followed by the contents of the parent's "Message-ID:" field (if
 any).  If the parent has none of the "References:", "In-Reply-To:",
 or "Message-ID:" fields, then the new message will have no
 "References:" field.
 Note: Some implementations parse the "References:" field to display
 the "thread of the discussion".  These implementations assume that
 each new message is a reply to a single parent and hence that they
 can walk backwards through the "References:" field to find the parent
 of each message listed there.  Therefore, trying to form a
 "References:" field for a reply that has multiple parents is
 discouraged and how to do so is not defined in this document.
 The message identifier (msg-id) itself MUST be a globally unique
 identifier for a message.  The generator of the message identifier
 MUST guarantee that the msg-id is unique.  There are several
 algorithms that can be used to accomplish this.  Since the msg-id has
 a similar syntax to angle-addr (identical except that comments and
 folding white space are not allowed), a good method is to put the
 domain name (or a domain literal IP address) of the host on which the
 message identifier was created on the right hand side of the "@", and
 put a combination of the current absolute date and time along with
 some other currently unique (perhaps sequential) identifier available
 on the system (for example, a process id number) on the left hand
 side.  Using a date on the left hand side and a domain name or domain
 literal on the right hand side makes it possible to guarantee
 uniqueness since no two hosts use the same domain name or IP address
 at the same time.  Though other algorithms will work, it is
 RECOMMENDED that the right hand side contain some domain identifier
 (either of the host itself or otherwise) such that the generator of
 the message identifier can guarantee the uniqueness of the left hand
 side within the scope of that domain.
 Semantically, the angle bracket characters are not part of the
 msg-id; the msg-id is what is contained between the two angle bracket
 characters.

Resnick Standards Track [Page 25] RFC 2822 Internet Message Format April 2001

3.6.5. Informational fields

 The informational fields are all optional.  The "Keywords:" field
 contains a comma-separated list of one or more words or
 quoted-strings. The "Subject:" and "Comments:" fields are
 unstructured fields as defined in section 2.2.1, and therefore may
 contain text or folding white space.

subject = "Subject:" unstructured CRLF

comments = "Comments:" unstructured CRLF

keywords = "Keywords:" phrase *("," phrase) CRLF

 These three fields are intended to have only human-readable content
 with information about the message.  The "Subject:" field is the most
 common and contains a short string identifying the topic of the
 message.  When used in a reply, the field body MAY start with the
 string "Re: " (from the Latin "res", in the matter of) followed by
 the contents of the "Subject:" field body of the original message.
 If this is done, only one instance of the literal string "Re: " ought
 to be used since use of other strings or more than one instance can
 lead to undesirable consequences.  The "Comments:" field contains any
 additional comments on the text of the body of the message.  The
 "Keywords:" field contains a comma-separated list of important words
 and phrases that might be useful for the recipient.

3.6.6. Resent fields

 Resent fields SHOULD be added to any message that is reintroduced by
 a user into the transport system.  A separate set of resent fields
 SHOULD be added each time this is done.  All of the resent fields
 corresponding to a particular resending of the message SHOULD be
 together.  Each new set of resent fields is prepended to the message;
 that is, the most recent set of resent fields appear earlier in the
 message.  No other fields in the message are changed when resent
 fields are added.
 Each of the resent fields corresponds to a particular field elsewhere
 in the syntax.  For instance, the "Resent-Date:" field corresponds to
 the "Date:" field and the "Resent-To:" field corresponds to the "To:"
 field.  In each case, the syntax for the field body is identical to
 the syntax given previously for the corresponding field.
 When resent fields are used, the "Resent-From:" and "Resent-Date:"
 fields MUST be sent.  The "Resent-Message-ID:" field SHOULD be sent.
 "Resent-Sender:" SHOULD NOT be used if "Resent-Sender:" would be
 identical to "Resent-From:".

Resnick Standards Track [Page 26] RFC 2822 Internet Message Format April 2001

resent-date = "Resent-Date:" date-time CRLF

resent-from = "Resent-From:" mailbox-list CRLF

resent-sender = "Resent-Sender:" mailbox CRLF

resent-to = "Resent-To:" address-list CRLF

resent-cc = "Resent-Cc:" address-list CRLF

resent-bcc = "Resent-Bcc:" (address-list / [CFWS]) CRLF

resent-msg-id = "Resent-Message-ID:" msg-id CRLF

 Resent fields are used to identify a message as having been
 reintroduced into the transport system by a user.  The purpose of
 using resent fields is to have the message appear to the final
 recipient as if it were sent directly by the original sender, with
 all of the original fields remaining the same.  Each set of resent
 fields correspond to a particular resending event.  That is, if a
 message is resent multiple times, each set of resent fields gives
 identifying information for each individual time.  Resent fields are
 strictly informational.  They MUST NOT be used in the normal
 processing of replies or other such automatic actions on messages.
 Note: Reintroducing a message into the transport system and using
 resent fields is a different operation from "forwarding".
 "Forwarding" has two meanings: One sense of forwarding is that a mail
 reading program can be told by a user to forward a copy of a message
 to another person, making the forwarded message the body of the new
 message.  A forwarded message in this sense does not appear to have
 come from the original sender, but is an entirely new message from
 the forwarder of the message.  On the other hand, forwarding is also
 used to mean when a mail transport program gets a message and
 forwards it on to a different destination for final delivery.  Resent
 header fields are not intended for use with either type of
 forwarding.
 The resent originator fields indicate the mailbox of the person(s) or
 system(s) that resent the message.  As with the regular originator
 fields, there are two forms: a simple "Resent-From:" form which
 contains the mailbox of the individual doing the resending, and the
 more complex form, when one individual (identified in the
 "Resent-Sender:" field) resends a message on behalf of one or more
 others (identified in the "Resent-From:" field).
 Note: When replying to a resent message, replies behave just as they
 would with any other message, using the original "From:",

Resnick Standards Track [Page 27] RFC 2822 Internet Message Format April 2001

 "Reply-To:", "Message-ID:", and other fields.  The resent fields are
 only informational and MUST NOT be used in the normal processing of
 replies.
 The "Resent-Date:" indicates the date and time at which the resent
 message is dispatched by the resender of the message.  Like the
 "Date:" field, it is not the date and time that the message was
 actually transported.
 The "Resent-To:", "Resent-Cc:", and "Resent-Bcc:" fields function
 identically to the "To:", "Cc:", and "Bcc:" fields respectively,
 except that they indicate the recipients of the resent message, not
 the recipients of the original message.
 The "Resent-Message-ID:" field provides a unique identifier for the
 resent message.

3.6.7. Trace fields

 The trace fields are a group of header fields consisting of an
 optional "Return-Path:" field, and one or more "Received:" fields.
 The "Return-Path:" header field contains a pair of angle brackets
 that enclose an optional addr-spec.  The "Received:" field contains a
 (possibly empty) list of name/value pairs followed by a semicolon and
 a date-time specification.  The first item of the name/value pair is
 defined by item-name, and the second item is either an addr-spec, an
 atom, a domain, or a msg-id.  Further restrictions may be applied to
 the syntax of the trace fields by standards that provide for their
 use, such as [RFC2821].

trace = [return]

                      1*received

return = "Return-Path:" path CRLF

path = ([CFWS] "<" ([CFWS] / addr-spec) ">" [CFWS]) /

                      obs-path

received = "Received:" name-val-list ";" date-time CRLF

name-val-list = [CFWS] [name-val-pair *(CFWS name-val-pair)]

name-val-pair = item-name CFWS item-value

item-name = ALPHA *(["-"] (ALPHA / DIGIT))

item-value = 1*angle-addr / addr-spec /

                       atom / domain / msg-id

Resnick Standards Track [Page 28] RFC 2822 Internet Message Format April 2001

 A full discussion of the Internet mail use of trace fields is
 contained in [RFC2821].  For the purposes of this standard, the trace
 fields are strictly informational, and any formal interpretation of
 them is outside of the scope of this document.

3.6.8. Optional fields

 Fields may appear in messages that are otherwise unspecified in this
 standard.  They MUST conform to the syntax of an optional-field.
 This is a field name, made up of the printable US-ASCII characters
 except SP and colon, followed by a colon, followed by any text which
 conforms to unstructured.
 The field names of any optional-field MUST NOT be identical to any
 field name specified elsewhere in this standard.

optional-field = field-name ":" unstructured CRLF

field-name = 1*ftext

ftext = %d33-57 / ; Any character except

                      %d59-126                ;  controls, SP, and
                                              ;  ":".
 For the purposes of this standard, any optional field is
 uninterpreted.

4. Obsolete Syntax

 Earlier versions of this standard allowed for different (usually more
 liberal) syntax than is allowed in this version.  Also, there have
 been syntactic elements used in messages on the Internet whose
 interpretation have never been documented.  Though some of these
 syntactic forms MUST NOT be generated according to the grammar in
 section 3, they MUST be accepted and parsed by a conformant receiver.
 This section documents many of these syntactic elements.  Taking the
 grammar in section 3 and adding the definitions presented in this
 section will result in the grammar to use for interpretation of
 messages.
 Note: This section identifies syntactic forms that any implementation
 MUST reasonably interpret.  However, there are certainly Internet
 messages which do not conform to even the additional syntax given in
 this section.  The fact that a particular form does not appear in any
 section of this document is not justification for computer programs
 to crash or for malformed data to be irretrievably lost by any
 implementation.  To repeat an example, though this document requires
 lines in messages to be no longer than 998 characters, silently

Resnick Standards Track [Page 29] RFC 2822 Internet Message Format April 2001

 discarding the 999th and subsequent characters in a line without
 warning would still be bad behavior for an implementation.  It is up
 to the implementation to deal with messages robustly.
 One important difference between the obsolete (interpreting) and the
 current (generating) syntax is that in structured header field bodies
 (i.e., between the colon and the CRLF of any structured header
 field), white space characters, including folding white space, and
 comments can be freely inserted between any syntactic tokens.  This
 allows many complex forms that have proven difficult for some
 implementations to parse.
 Another key difference between the obsolete and the current syntax is
 that the rule in section 3.2.3 regarding lines composed entirely of
 white space in comments and folding white space does not apply.  See
 the discussion of folding white space in section 4.2 below.
 Finally, certain characters that were formerly allowed in messages
 appear in this section.  The NUL character (ASCII value 0) was once
 allowed, but is no longer for compatibility reasons.  CR and LF were
 allowed to appear in messages other than as CRLF; this use is also
 shown here.
 Other differences in syntax and semantics are noted in the following
 sections.

4.1. Miscellaneous obsolete tokens

 These syntactic elements are used elsewhere in the obsolete syntax or
 in the main syntax.  The obs-char and obs-qp elements each add ASCII
 value 0. Bare CR and bare LF are added to obs-text and obs-utext.
 The period character is added to obs-phrase. The obs-phrase-list
 provides for "empty" elements in a comma-separated list of phrases.
 Note: The "period" (or "full stop") character (".") in obs-phrase is
 not a form that was allowed in earlier versions of this or any other
 standard.  Period (nor any other character from specials) was not
 allowed in phrase because it introduced a parsing difficulty
 distinguishing between phrases and portions of an addr-spec (see
 section 4.4).  It appears here because the period character is
 currently used in many messages in the display-name portion of
 addresses, especially for initials in names, and therefore must be
 interpreted properly.  In the future, period may appear in the
 regular syntax of phrase.

obs-qp = "\" (%d0-127)

obs-text = *LF *CR *(obs-char *LF *CR)

Resnick Standards Track [Page 30] RFC 2822 Internet Message Format April 2001

obs-char = %d0-9 / %d11 / ; %d0-127 except CR and

                      %d12 / %d14-127         ;  LF

obs-utext = obs-text

obs-phrase = word *(word / "." / CFWS)

obs-phrase-list = phrase / 1*([phrase] [CFWS] "," [CFWS]) [phrase]

 Bare CR and bare LF appear in messages with two different meanings.
 In many cases, bare CR or bare LF are used improperly instead of CRLF
 to indicate line separators.  In other cases, bare CR and bare LF are
 used simply as ASCII control characters with their traditional ASCII
 meanings.

4.2. Obsolete folding white space

 In the obsolete syntax, any amount of folding white space MAY be
 inserted where the obs-FWS rule is allowed.  This creates the
 possibility of having two consecutive "folds" in a line, and
 therefore the possibility that a line which makes up a folded header
 field could be composed entirely of white space.
 obs-FWS         =       1*WSP *(CRLF 1*WSP)

4.3. Obsolete Date and Time

 The syntax for the obsolete date format allows a 2 digit year in the
 date field and allows for a list of alphabetic time zone
 specifications that were used in earlier versions of this standard.
 It also permits comments and folding white space between many of the
 tokens.

obs-day-of-week = [CFWS] day-name [CFWS]

obs-year = [CFWS] 2*DIGIT [CFWS]

obs-month = CFWS month-name CFWS

obs-day = [CFWS] 1*2DIGIT [CFWS]

obs-hour = [CFWS] 2DIGIT [CFWS]

obs-minute = [CFWS] 2DIGIT [CFWS]

obs-second = [CFWS] 2DIGIT [CFWS]

obs-zone = "UT" / "GMT" / ; Universal Time

Resnick Standards Track [Page 31] RFC 2822 Internet Message Format April 2001

                                              ; North American UT
                                              ; offsets
                      "EST" / "EDT" /         ; Eastern:  - 5/ - 4
                      "CST" / "CDT" /         ; Central:  - 6/ - 5
                      "MST" / "MDT" /         ; Mountain: - 7/ - 6
                      "PST" / "PDT" /         ; Pacific:  - 8/ - 7
                      %d65-73 /               ; Military zones - "A"
                      %d75-90 /               ; through "I" and "K"
                      %d97-105 /              ; through "Z", both
                      %d107-122               ; upper and lower case
 Where a two or three digit year occurs in a date, the year is to be
 interpreted as follows: If a two digit year is encountered whose
 value is between 00 and 49, the year is interpreted by adding 2000,
 ending up with a value between 2000 and 2049.  If a two digit year is
 encountered with a value between 50 and 99, or any three digit year
 is encountered, the year is interpreted by adding 1900.
 In the obsolete time zone, "UT" and "GMT" are indications of
 "Universal Time" and "Greenwich Mean Time" respectively and are both
 semantically identical to "+0000".
 The remaining three character zones are the US time zones.  The first
 letter, "E", "C", "M", or "P" stands for "Eastern", "Central",
 "Mountain" and "Pacific".  The second letter is either "S" for
 "Standard" time, or "D" for "Daylight" (or summer) time.  Their
 interpretations are as follows:
 EDT is semantically equivalent to -0400
 EST is semantically equivalent to -0500
 CDT is semantically equivalent to -0500
 CST is semantically equivalent to -0600
 MDT is semantically equivalent to -0600
 MST is semantically equivalent to -0700
 PDT is semantically equivalent to -0700
 PST is semantically equivalent to -0800
 The 1 character military time zones were defined in a non-standard
 way in [RFC822] and are therefore unpredictable in their meaning.
 The original definitions of the military zones "A" through "I" are
 equivalent to "+0100" through "+0900" respectively; "K", "L", and "M"
 are equivalent to  "+1000", "+1100", and "+1200" respectively; "N"
 through "Y" are equivalent to "-0100" through "-1200" respectively;
 and "Z" is equivalent to "+0000".  However, because of the error in
 [RFC822], they SHOULD all be considered equivalent to "-0000" unless
 there is out-of-band information confirming their meaning.

Resnick Standards Track [Page 32] RFC 2822 Internet Message Format April 2001

 Other multi-character (usually between 3 and 5) alphabetic time zones
 have been used in Internet messages.  Any such time zone whose
 meaning is not known SHOULD be considered equivalent to "-0000"
 unless there is out-of-band information confirming their meaning.

4.4. Obsolete Addressing

 There are three primary differences in addressing.  First, mailbox
 addresses were allowed to have a route portion before the addr-spec
 when enclosed in "<" and ">".  The route is simply a comma-separated
 list of domain names, each preceded by "@", and the list terminated
 by a colon.  Second, CFWS were allowed between the period-separated
 elements of local-part and domain (i.e., dot-atom was not used).  In
 addition, local-part is allowed to contain quoted-string in addition
 to just atom.  Finally, mailbox-list and address-list were allowed to
 have "null" members.  That is, there could be two or more commas in
 such a list with nothing in between them.

obs-angle-addr = [CFWS] "<" [obs-route] addr-spec ">" [CFWS]

obs-route = [CFWS] obs-domain-list ":" [CFWS]

obs-domain-list = "@" domain *(*(CFWS / "," ) [CFWS] "@" domain)

obs-local-part = word *("." word)

obs-domain = atom *("." atom)

obs-mbox-list = 1*([mailbox] [CFWS] "," [CFWS]) [mailbox]

obs-addr-list = 1*([address] [CFWS] "," [CFWS]) [address]

 When interpreting addresses, the route portion SHOULD be ignored.

4.5. Obsolete header fields

 Syntactically, the primary difference in the obsolete field syntax is
 that it allows multiple occurrences of any of the fields and they may
 occur in any order.  Also, any amount of white space is allowed
 before the ":" at the end of the field name.

obs-fields = *(obs-return /

                      obs-received /
                      obs-orig-date /
                      obs-from /
                      obs-sender /
                      obs-reply-to /
                      obs-to /

Resnick Standards Track [Page 33] RFC 2822 Internet Message Format April 2001

                      obs-cc /
                      obs-bcc /
                      obs-message-id /
                      obs-in-reply-to /
                      obs-references /
                      obs-subject /
                      obs-comments /
                      obs-keywords /
                      obs-resent-date /
                      obs-resent-from /
                      obs-resent-send /
                      obs-resent-rply /
                      obs-resent-to /
                      obs-resent-cc /
                      obs-resent-bcc /
                      obs-resent-mid /
                      obs-optional)
 Except for destination address fields (described in section 4.5.3),
 the interpretation of multiple occurrences of fields is unspecified.
 Also, the interpretation of trace fields and resent fields which do
 not occur in blocks prepended to the message is unspecified as well.
 Unless otherwise noted in the following sections, interpretation of
 other fields is identical to the interpretation of their non-obsolete
 counterparts in section 3.

4.5.1. Obsolete origination date field

obs-orig-date = "Date" *WSP ":" date-time CRLF

4.5.2. Obsolete originator fields

obs-from = "From" *WSP ":" mailbox-list CRLF

obs-sender = "Sender" *WSP ":" mailbox CRLF

obs-reply-to = "Reply-To" *WSP ":" mailbox-list CRLF

4.5.3. Obsolete destination address fields

obs-to = "To" *WSP ":" address-list CRLF

obs-cc = "Cc" *WSP ":" address-list CRLF

obs-bcc = "Bcc" *WSP ":" (address-list / [CFWS]) CRLF

Resnick Standards Track [Page 34] RFC 2822 Internet Message Format April 2001

 When multiple occurrences of destination address fields occur in a
 message, they SHOULD be treated as if the address-list in the first
 occurrence of the field is combined with the address lists of the
 subsequent occurrences by adding a comma and concatenating.

4.5.4. Obsolete identification fields

 The obsolete "In-Reply-To:" and "References:" fields differ from the
 current syntax in that they allow phrase (words or quoted strings) to
 appear.  The obsolete forms of the left and right sides of msg-id
 allow interspersed CFWS, making them syntactically identical to
 local-part and domain respectively.

obs-message-id = "Message-ID" *WSP ":" msg-id CRLF

obs-in-reply-to = "In-Reply-To" *WSP ":" *(phrase / msg-id) CRLF

obs-references = "References" *WSP ":" *(phrase / msg-id) CRLF

obs-id-left = local-part

obs-id-right = domain

 For purposes of interpretation, the phrases in the "In-Reply-To:" and
 "References:" fields are ignored.
 Semantically, none of the optional CFWS surrounding the local-part
 and the domain are part of the obs-id-left and obs-id-right
 respectively.

4.5.5. Obsolete informational fields

obs-subject = "Subject" *WSP ":" unstructured CRLF

obs-comments = "Comments" *WSP ":" unstructured CRLF

obs-keywords = "Keywords" *WSP ":" obs-phrase-list CRLF

4.5.6. Obsolete resent fields

 The obsolete syntax adds a "Resent-Reply-To:" field, which consists
 of the field name, the optional comments and folding white space, the
 colon, and a comma separated list of addresses.

obs-resent-from = "Resent-From" *WSP ":" mailbox-list CRLF

obs-resent-send = "Resent-Sender" *WSP ":" mailbox CRLF

Resnick Standards Track [Page 35] RFC 2822 Internet Message Format April 2001

obs-resent-date = "Resent-Date" *WSP ":" date-time CRLF

obs-resent-to = "Resent-To" *WSP ":" address-list CRLF

obs-resent-cc = "Resent-Cc" *WSP ":" address-list CRLF

obs-resent-bcc = "Resent-Bcc" *WSP ":"

                       (address-list / [CFWS]) CRLF

obs-resent-mid = "Resent-Message-ID" *WSP ":" msg-id CRLF

obs-resent-rply = "Resent-Reply-To" *WSP ":" address-list CRLF

 As with other resent fields, the "Resent-Reply-To:" field is to be
 treated as trace information only.

4.5.7. Obsolete trace fields

 The obs-return and obs-received are again given here as template
 definitions, just as return and received are in section 3.  Their
 full syntax is given in [RFC2821].

obs-return = "Return-Path" *WSP ":" path CRLF

obs-received = "Received" *WSP ":" name-val-list CRLF

obs-path = obs-angle-addr

4.5.8. Obsolete optional fields

obs-optional = field-name *WSP ":" unstructured CRLF

5. Security Considerations

 Care needs to be taken when displaying messages on a terminal or
 terminal emulator.  Powerful terminals may act on escape sequences
 and other combinations of ASCII control characters with a variety of
 consequences.  They can remap the keyboard or permit other
 modifications to the terminal which could lead to denial of service
 or even damaged data.  They can trigger (sometimes programmable)
 answerback messages which can allow a message to cause commands to be
 issued on the recipient's behalf.  They can also effect the operation
 of terminal attached devices such as printers.  Message viewers may
 wish to strip potentially dangerous terminal escape sequences from
 the message prior to display.  However, other escape sequences appear
 in messages for useful purposes (cf. [RFC2045, RFC2046, RFC2047,
 RFC2048, RFC2049, ISO2022]) and therefore should not be stripped
 indiscriminately.

Resnick Standards Track [Page 36] RFC 2822 Internet Message Format April 2001

 Transmission of non-text objects in messages raises additional
 security issues.  These issues are discussed in [RFC2045, RFC2046,
 RFC2047, RFC2048, RFC2049].
 Many implementations use the "Bcc:" (blind carbon copy) field
 described in section 3.6.3 to facilitate sending messages to
 recipients without revealing the addresses of one or more of the
 addressees to the other recipients.  Mishandling this use of "Bcc:"
 has implications for confidential information that might be revealed,
 which could eventually lead to security problems through knowledge of
 even the existence of a particular mail address.  For example, if
 using the first method described in section 3.6.3, where the "Bcc:"
 line is removed from the message, blind recipients have no explicit
 indication that they have been sent a blind copy, except insofar as
 their address does not appear in the message header.  Because of
 this, one of the blind addressees could potentially send a reply to
 all of the shown recipients and accidentally reveal that the message
 went to the blind recipient.  When the second method from section
 3.6.3 is used, the blind recipient's address appears in the "Bcc:"
 field of a separate copy of the message. If the "Bcc:" field sent
 contains all of the blind addressees, all of the "Bcc:" recipients
 will be seen by each "Bcc:" recipient.  Even if a separate message is
 sent to each "Bcc:" recipient with only the individual's address,
 implementations still need to be careful to process replies to the
 message as per section 3.6.3 so as not to accidentally reveal the
 blind recipient to other recipients.

6. Bibliography

 [ASCII]    American National Standards Institute (ANSI), Coded
            Character Set - 7-Bit American National Standard Code for
            Information Interchange, ANSI X3.4, 1986.
 [ISO2022] International Organization for Standardization (ISO),
            Information processing - ISO 7-bit and 8-bit coded
            character sets - Code extension techniques, Third edition
            - 1986-05-01, ISO 2022, 1986.
 [RFC822]   Crocker, D., "Standard for the Format of ARPA Internet
            Text Messages", RFC 822, August 1982.
 [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.

Resnick Standards Track [Page 37] RFC 2822 Internet Message Format April 2001

 [RFC2047]  Moore, K., "Multipurpose Internet Mail Extensions (MIME)
            Part Three: Message Header Extensions for Non-ASCII Text",
            RFC 2047, November 1996.
 [RFC2048]  Freed, N., Klensin, J. and J. Postel, "Multipurpose
            Internet Mail Extensions (MIME) Part Four: Format of
            Internet Message Bodies", RFC 2048, November 1996.
 [RFC2049]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
            Extensions (MIME) Part Five: Conformance Criteria and
            Examples", RFC 2049, November 1996.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2234]  Crocker, D., Editor, and P. Overell, "Augmented BNF for
            Syntax Specifications: ABNF", RFC 2234, November 1997.
 [RFC2821]  Klensin, J., Editor, "Simple Mail Transfer Protocol", RFC
            2821, March 2001.
 [STD3]     Braden, R., "Host Requirements", STD 3, RFC 1122 and RFC
            1123, October 1989.
 [STD12]    Mills, D., "Network Time Protocol", STD 12, RFC 1119,
            September 1989.
 [STD13]    Mockapetris, P., "Domain Name System", STD 13, RFC 1034
            and RFC 1035,  November 1987.
 [STD14]    Partridge, C., "Mail Routing and the Domain System", STD
            14, RFC 974, January 1986.

7. Editor's Address

 Peter W. Resnick
 QUALCOMM Incorporated
 5775 Morehouse Drive
 San Diego, CA 92121-1714
 USA
 Phone: +1 858 651 4478
 Fax:   +1 858 651 1102
 EMail: presnick@qualcomm.com

Resnick Standards Track [Page 38] RFC 2822 Internet Message Format April 2001

8. Acknowledgements

 Many people contributed to this document.  They included folks who
 participated in the Detailed Revision and Update of Messaging
 Standards (DRUMS) Working Group of the Internet Engineering Task
 Force (IETF), the chair of DRUMS, the Area Directors of the IETF, and
 people who simply sent their comments in via e-mail.  The editor is
 deeply indebted to them all and thanks them sincerely.  The below
 list includes everyone who sent e-mail concerning this document.
 Hopefully, everyone who contributed is named here:
 Matti Aarnio              Barry Finkel           Larry Masinter
 Tanaka Akira              Erik Forsberg          Denis McKeon
 Russ Allbery              Chuck Foster           William P McQuillan
 Eric Allman               Paul Fox               Alexey Melnikov
 Harald Tveit Alvestrand   Klaus M. Frank         Perry E. Metzger
 Ran Atkinson              Ned Freed              Steven Miller
 Jos Backus                Jochen Friedrich       Keith Moore
 Bruce Balden              Randall C. Gellens     John Gardiner Myers
 Dave Barr                 Sukvinder Singh Gill   Chris Newman
 Alan Barrett              Tim Goodwin            John W. Noerenberg
 John Beck                 Philip Guenther        Eric Norman
 J. Robert von Behren      Tony Hansen            Mike O'Dell
 Jos den Bekker            John Hawkinson         Larry Osterman
 D. J. Bernstein           Philip Hazel           Paul Overell
 James Berriman            Kai Henningsen         Jacob Palme
 Norbert Bollow            Robert Herriot         Michael A. Patton
 Raj Bose                  Paul Hethmon           Uzi Paz
 Antony Bowesman           Jim Hill               Michael A. Quinlan
 Scott Bradner             Paul E. Hoffman        Eric S. Raymond
 Randy Bush                Steve Hole             Sam Roberts
 Tom Byrer                 Kari Hurtta            Hugh Sasse
 Bruce Campbell            Marco S. Hyman         Bart Schaefer
 Larry Campbell            Ofer Inbar             Tom Scola
 W. J. Carpenter           Olle Jarnefors         Wolfgang Segmuller
 Michael Chapman           Kevin Johnson          Nick Shelness
 Richard Clayton           Sudish Joseph          John Stanley
 Maurizio Codogno          Maynard Kang           Einar Stefferud
 Jim Conklin               Prabhat Keni           Jeff Stephenson
 R. Kelley Cook            John C. Klensin        Bernard Stern
 Steve Coya                Graham Klyne           Peter Sylvester
 Mark Crispin              Brad Knowles           Mark Symons
 Dave Crocker              Shuhei Kobayashi       Eric Thomas
 Matt Curtin               Peter Koch             Lee Thompson
 Michael D'Errico          Dan Kohn               Karel De Vriendt
 Cyrus Daboo               Christian Kuhtz        Matthew Wall
 Jutta Degener             Anand Kumria           Rolf Weber
 Mark Delany               Steen Larsen           Brent B. Welch

Resnick Standards Track [Page 39] RFC 2822 Internet Message Format April 2001

 Steve Dorner              Eliot Lear             Dan Wing
 Harold A. Driscoll        Barry Leiba            Jack De Winter
 Michael Elkins            Jay Levitt             Gregory J. Woodhouse
 Robert Elz                Lars-Johan Liman       Greg A. Woods
 Johnny Eriksson           Charles Lindsey        Kazu Yamamoto
 Erik E. Fair              Pete Loshin            Alain Zahm
 Roger Fajman              Simon Lyall            Jamie Zawinski
 Patrik Faltstrom          Bill Manning           Timothy S. Zurcher
 Claus Andre Farber        John Martin

Resnick Standards Track [Page 40] RFC 2822 Internet Message Format April 2001

Appendix A. Example messages

 This section presents a selection of messages.  These are intended to
 assist in the implementation of this standard, but should not be
 taken as normative; that is to say, although the examples in this
 section were carefully reviewed, if there happens to be a conflict
 between these examples and the syntax described in sections 3 and 4
 of this document, the syntax in those sections is to be taken as
 correct.
 Messages are delimited in this section between lines of "----".  The
 "----" lines are not part of the message itself.

A.1. Addressing examples

 The following are examples of messages that might be sent between two
 individuals.

A.1.1. A message from one person to another with simple addressing

 This could be called a canonical message.  It has a single author,
 John Doe, a single recipient, Mary Smith, a subject, the date, a
 message identifier, and a textual message in the body.

From: John Doe jdoe@machine.example To: Mary Smith mary@example.net Subject: Saying Hello Date: Fri, 21 Nov 1997 09:55:06 -0600 Message-ID: 1234@local.machine.example

This is a message just to say hello. So, "Hello".


Resnick Standards Track [Page 41] RFC 2822 Internet Message Format April 2001

 If John's secretary Michael actually sent the message, though John
 was the author and replies to this message should go back to him, the
 sender field would be used:

From: John Doe jdoe@machine.example Sender: Michael Jones mjones@machine.example To: Mary Smith mary@example.net Subject: Saying Hello Date: Fri, 21 Nov 1997 09:55:06 -0600 Message-ID: 1234@local.machine.example

This is a message just to say hello. So, "Hello".


A.1.2. Different types of mailboxes

 This message includes multiple addresses in the destination fields
 and also uses several different forms of addresses.

From: "Joe Q. Public" john.q.public@example.com To: Mary Smith mary@x.test, jdoe@example.org, Who? one@y.test Cc: boss@nil.test, "Giant; \"Big\" Box" sysservices@example.net Date: Tue, 1 Jul 2003 10:52:37 +0200 Message-ID: 5678.21-Nov-1997@example.com

Hi everyone.


 Note that the display names for Joe Q. Public and Giant; "Big" Box
 needed to be enclosed in double-quotes because the former contains
 the period and the latter contains both semicolon and double-quote
 characters (the double-quote characters appearing as quoted-pair
 construct).  Conversely, the display name for Who? could appear
 without them because the question mark is legal in an atom.  Notice
 also that jdoe@example.org and boss@nil.test have no display names
 associated with them at all, and jdoe@example.org uses the simpler
 address form without the angle brackets.

Resnick Standards Track [Page 42] RFC 2822 Internet Message Format April 2001

A.1.3. Group addresses


From: Pete pete@silly.example To: A Group:Chris Jones c@a.test,joe@where.test,John jdoe@one.test; Cc: Undisclosed recipients:; Date: Thu, 13 Feb 1969 23:32:54 -0330 Message-ID: testabcd.1234@silly.example

Testing.


 In this message, the "To:" field has a single group recipient named A
 Group which contains 3 addresses, and a "Cc:" field with an empty
 group recipient named Undisclosed recipients.

A.2. Reply messages

 The following is a series of three messages that make up a
 conversation thread between John and Mary.  John firsts sends a
 message to Mary, Mary then replies to John's message, and then John
 replies to Mary's reply message.
 Note especially the "Message-ID:", "References:", and "In-Reply-To:"
 fields in each message.

From: John Doe jdoe@machine.example To: Mary Smith mary@example.net Subject: Saying Hello Date: Fri, 21 Nov 1997 09:55:06 -0600 Message-ID: 1234@local.machine.example

This is a message just to say hello. So, "Hello".


Resnick Standards Track [Page 43] RFC 2822 Internet Message Format April 2001

 When sending replies, the Subject field is often retained, though
 prepended with "Re: " as described in section 3.6.5.

From: Mary Smith mary@example.net To: John Doe jdoe@machine.example Reply-To: "Mary Smith: Personal Account" smith@home.example Subject: Re: Saying Hello Date: Fri, 21 Nov 1997 10:01:10 -0600 Message-ID: 3456@example.net In-Reply-To: 1234@local.machine.example References: 1234@local.machine.example

This is a reply to your hello.


 Note the "Reply-To:" field in the above message.  When John replies
 to Mary's message above, the reply should go to the address in the
 "Reply-To:" field instead of the address in the "From:" field.

To: "Mary Smith: Personal Account" smith@home.example From: John Doe jdoe@machine.example Subject: Re: Saying Hello Date: Fri, 21 Nov 1997 11:00:00 -0600 Message-ID: abcd.1234@local.machine.tld In-Reply-To: 3456@example.net References: 1234@local.machine.example 3456@example.net

This is a reply to your reply.


A.3. Resent messages

 Start with the message that has been used as an example several
 times:

From: John Doe jdoe@machine.example To: Mary Smith mary@example.net Subject: Saying Hello Date: Fri, 21 Nov 1997 09:55:06 -0600 Message-ID: 1234@local.machine.example

This is a message just to say hello. So, "Hello".


Resnick Standards Track [Page 44] RFC 2822 Internet Message Format April 2001

 Say that Mary, upon receiving this message, wishes to send a copy of
 the message to Jane such that (a) the message would appear to have
 come straight from John; (b) if Jane replies to the message, the
 reply should go back to John; and (c) all of the original
 information, like the date the message was originally sent to Mary,
 the message identifier, and the original addressee, is preserved.  In
 this case, resent fields are prepended to the message:

Resent-From: Mary Smith mary@example.net Resent-To: Jane Brown j-brown@other.example Resent-Date: Mon, 24 Nov 1997 14:22:01 -0800 Resent-Message-ID: 78910@example.net From: John Doe jdoe@machine.example To: Mary Smith mary@example.net Subject: Saying Hello Date: Fri, 21 Nov 1997 09:55:06 -0600 Message-ID: 1234@local.machine.example

This is a message just to say hello. So, "Hello".


 If Jane, in turn, wished to resend this message to another person,
 she would prepend her own set of resent header fields to the above
 and send that.

Resnick Standards Track [Page 45] RFC 2822 Internet Message Format April 2001

A.4. Messages with trace fields

 As messages are sent through the transport system as described in
 [RFC2821], trace fields are prepended to the message.  The following
 is an example of what those trace fields might look like.  Note that
 there is some folding white space in the first one since these lines
 can be long.

Received: from x.y.test

 by example.net
 via TCP
 with ESMTP
 id ABC12345
 for <mary@example.net>;  21 Nov 1997 10:05:43 -0600

Received: from machine.example by x.y.test; 21 Nov 1997 10:01:22 -0600 From: John Doe jdoe@machine.example To: Mary Smith mary@example.net Subject: Saying Hello Date: Fri, 21 Nov 1997 09:55:06 -0600 Message-ID: 1234@local.machine.example

This is a message just to say hello. So, "Hello".


Resnick Standards Track [Page 46] RFC 2822 Internet Message Format April 2001

A.5. White space, comments, and other oddities

 White space, including folding white space, and comments can be
 inserted between many of the tokens of fields.  Taking the example
 from A.1.3, white space and comments can be inserted into all of the
 fields.

From: Pete(A wonderful \) chap) <pete(his account)@silly.test(his host)> To:A Group(Some people)

   :Chris Jones <c@(Chris's host.)public.example>,
       joe@example.org,
John <jdoe@one.test> (my dear friend); (the end of the group)

Cc:(Empty list)(start)Undisclosed recipients :(nobody(that I know)) ; Date: Thu,

    13
      Feb
        1969
    23:32
             -0330 (Newfoundland Time)

Message-ID: testabcd.1234@silly.test

Testing.


 The above example is aesthetically displeasing, but perfectly legal.
 Note particularly (1) the comments in the "From:" field (including
 one that has a ")" character appearing as part of a quoted-pair); (2)
 the white space absent after the ":" in the "To:" field as well as
 the comment and folding white space after the group name, the special
 character (".") in the comment in Chris Jones's address, and the
 folding white space before and after "joe@example.org,"; (3) the
 multiple and nested comments in the "Cc:" field as well as the
 comment immediately following the ":" after "Cc"; (4) the folding
 white space (but no comments except at the end) and the missing
 seconds in the time of the date field; and (5) the white space before
 (but not within) the identifier in the "Message-ID:" field.

A.6. Obsoleted forms

 The following are examples of obsolete (that is, the "MUST NOT
 generate") syntactic elements described in section 4 of this
 document.

Resnick Standards Track [Page 47] RFC 2822 Internet Message Format April 2001

A.6.1. Obsolete addressing

 Note in the below example the lack of quotes around Joe Q. Public,
 the route that appears in the address for Mary Smith, the two commas
 that appear in the "To:" field, and the spaces that appear around the
 "." in the jdoe address.

From: Joe Q. Public john.q.public@example.com To: Mary Smith <@machine.tld:mary@example.net>, , jdoe@test . example Date: Tue, 1 Jul 2003 10:52:37 +0200 Message-ID: 5678.21-Nov-1997@example.com

Hi everyone.


A.6.2. Obsolete dates

 The following message uses an obsolete date format, including a non-
 numeric time zone and a two digit year.  Note that although the
 day-of-week is missing, that is not specific to the obsolete syntax;
 it is optional in the current syntax as well.

From: John Doe jdoe@machine.example To: Mary Smith mary@example.net Subject: Saying Hello Date: 21 Nov 97 09:55:06 GMT Message-ID: 1234@local.machine.example

This is a message just to say hello. So, "Hello".


A.6.3. Obsolete white space and comments

 White space and comments can appear between many more elements than
 in the current syntax.  Also, folding lines that are made up entirely
 of white space are legal.

Resnick Standards Track [Page 48] RFC 2822 Internet Message Format April 2001


From : John Doe <jdoe@machine(comment). example> To : Mary Smith mary@example.net Subject : Saying Hello Date : Fri, 21 Nov 1997 09(comment): 55 : 06 -0600 Message-ID : <1234 @ local(blah) .machine .example> This is a message just to say hello. So, "Hello". —- Note especially the second line of the "To:" field. It starts with two space characters. (Note that "" represent blank spaces.)

 Therefore, it is considered part of the folding as described in
 section 4.2.  Also, the comments and white space throughout
 addresses, dates, and message identifiers are all part of the
 obsolete syntax.

Appendix B. Differences from earlier standards

 This appendix contains a list of changes that have been made in the
 Internet Message Format from earlier standards, specifically [RFC822]
 and [STD3].  Items marked with an asterisk (*) below are items which
 appear in section 4 of this document and therefore can no longer be
 generated.
 1. Period allowed in obsolete form of phrase.
 2. ABNF moved out of document to [RFC2234].
 3. Four or more digits allowed for year.
 4. Header field ordering (and lack thereof) made explicit.
 5. Encrypted header field removed.
 6. Received syntax loosened to allow any token/value pair.
 7. Specifically allow and give meaning to "-0000" time zone.
 8. Folding white space is not allowed between every token.
 9. Requirement for destinations removed.
 10. Forwarding and resending redefined.
 11. Extension header fields no longer specifically called out.
 12. ASCII 0 (null) removed.*
 13. Folding continuation lines cannot contain only white space.*
 14. Free insertion of comments not allowed in date.*
 15. Non-numeric time zones not allowed.*
 16. Two digit years not allowed.*
 17. Three digit years interpreted, but not allowed for generation.
 18. Routes in addresses not allowed.*
 19. CFWS within local-parts and domains not allowed.*
 20. Empty members of address lists not allowed.*

Resnick Standards Track [Page 49] RFC 2822 Internet Message Format April 2001

 21. Folding white space between field name and colon not allowed.*
 22. Comments between field name and colon not allowed.
 23. Tightened syntax of in-reply-to and references.*
 24. CFWS within msg-id not allowed.*
 25. Tightened semantics of resent fields as informational only.
 26. Resent-Reply-To not allowed.*
 27. No multiple occurrences of fields (except resent and received).*
 28. Free CR and LF not allowed.*
 29. Routes in return path not allowed.*
 30. Line length limits specified.
 31. Bcc more clearly specified.

Appendix C. Notices

 Intellectual Property
 The IETF takes no position regarding the validity or scope of any
 intellectual property or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; neither does it represent that it
 has made any effort to identify any such rights.  Information on the
 IETF's procedures with respect to rights in standards-track and
 standards-related documentation can be found in BCP-11.  Copies of
 claims of rights made available for publication and any assurances of
 licenses to be made available, or the result of an attempt made to
 obtain a general license or permission for the use of such
 proprietary rights by implementors or users of this specification can
 be obtained from the IETF Secretariat.

Resnick Standards Track [Page 50] RFC 2822 Internet Message Format April 2001

Full Copyright Statement

 Copyright (C) The Internet Society (2001).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Resnick Standards Track [Page 51]

1)
[FWS] comment) / FWS)
 Throughout this standard, where FWS (the folding white space token)
 appears, it indicates a place where header folding, as discussed in
 section 2.2.3, may take place.  Wherever header folding appears in a
 message (that is, a header field body containing a CRLF followed by
 any WSP), header unfolding (removal of the CRLF) is performed before
 any further lexical analysis is performed on that header field
 according to this standard.  That is to say, any CRLF that appears in
 FWS is semantically "invisible."
 A comment is normally used in a structured field body to provide some
 human readable informational text.  Since a comment is allowed to
 contain FWS, folding is permitted within the comment.  Also note that
 since quoted-pair is allowed in a comment, the parentheses and
Resnick Standards Track [Page 11] RFC 2822 Internet Message Format April 2001
 backslash characters may appear in a comment so long as they appear
 as a quoted-pair.  Semantically, the enclosing parentheses are not
 part of the comment; the comment is what is contained between the two
 parentheses.  As stated earlier, the "\" in any quoted-pair and the
 CRLF in any FWS that appears within the comment are semantically
 "invisible" and therefore not part of the comment either.
 Runs of FWS, comment or CFWS that occur between lexical tokens in a
 structured field header are semantically interpreted as a single
 space character.
3.2.4. Atom
 Several productions in structured header field bodies are simply
 strings of certain basic characters.  Such productions are called
 atoms.
 Some of the structured header field bodies also allow the period
 character (".", ASCII value 46) within runs of atext.  An additional
 "dot-atom" token is defined for those purposes.
atext = ALPHA / DIGIT / ; Any character except controls,
                      "!" / "#" /     ;  SP, and specials.
                      "$" / "%" /     ;  Used for atoms
                      "&" / "'" /
                      "*" / "+" /
                      "-" / "/" /
                      "=" / "?" /
                      "^" / "_" /
                      "`" / "{" /
                      "|" / "}" /
                      "~"
atom = [CFWS] 1*atext [CFWS] dot-atom = [CFWS] dot-atom-text [CFWS] dot-atom-text = 1*atext *("." 1*atext)
 Both atom and dot-atom are interpreted as a single unit, comprised of
 the string of characters that make it up.  Semantically, the optional
 comments and FWS surrounding the rest of the characters are not part
 of the atom; the atom is only the run of atext characters in an atom,
 or the atext and "." characters in a dot-atom.
Resnick Standards Track [Page 12] RFC 2822 Internet Message Format April 2001 3.2.5. Quoted strings
 Strings of characters that include characters other than those
 allowed in atoms may be represented in a quoted string format, where
 the characters are surrounded by quote (DQUOTE, ASCII value 34)
 characters.
qtext = NO-WS-CTL / ; Non white space controls
                      %d33 /          ; The rest of the US-ASCII
                      %d35-91 /       ;  characters not including "\"
                      %d93-126        ;  or the quote character
qcontent = qtext / quoted-pair quoted-string = [CFWS]
                      DQUOTE *([FWS] qcontent) [FWS] DQUOTE
                      [CFWS]
 A quoted-string is treated as a unit.  That is, quoted-string is
 identical to atom, semantically.  Since a quoted-string is allowed to
 contain FWS, folding is permitted.  Also note that since quoted-pair
 is allowed in a quoted-string, the quote and backslash characters may
 appear in a quoted-string so long as they appear as a quoted-pair.
 Semantically, neither the optional CFWS outside of the quote
 characters nor the quote characters themselves are part of the
 quoted-string; the quoted-string is what is contained between the two
 quote characters.  As stated earlier, the "\" in any quoted-pair and
 the CRLF in any FWS/CFWS that appears within the quoted-string are
 semantically "invisible" and therefore not part of the quoted-string
 either.
3.2.6. Miscellaneous tokens
 Three additional tokens are defined, word and phrase for combinations
 of atoms and/or quoted-strings, and unstructured for use in
 unstructured header fields and in some places within structured
 header fields.
word = atom / quoted-string phrase = 1*word / obs-phrase Resnick Standards Track [Page 13] RFC 2822 Internet Message Format April 2001 utext = NO-WS-CTL / ; Non white space controls
                      %d33-126 /      ; The rest of US-ASCII
                      obs-utext
unstructured = *([FWS] utext) [FWS] 3.3. Date and Time Specification
 Date and time occur in several header fields.  This section specifies
 the syntax for a full date and time specification.  Though folding
 white space is permitted throughout the date-time specification, it
 is RECOMMENDED that a single space be used in each place that FWS
 appears (whether it is required or optional); some older
 implementations may not interpret other occurrences of folding white
 space correctly.
date-time = [ day-of-week "," ] date FWS time [CFWS] day-of-week = ([FWS] day-name) / obs-day-of-week day-name = "Mon" / "Tue" / "Wed" / "Thu" /
                      "Fri" / "Sat" / "Sun"
date = day month year year = 4*DIGIT / obs-year month = (FWS month-name FWS) / obs-month month-name = "Jan" / "Feb" / "Mar" / "Apr" /
                      "May" / "Jun" / "Jul" / "Aug" /
                      "Sep" / "Oct" / "Nov" / "Dec"
day = ([FWS] 1*2DIGIT) / obs-day time = time-of-day FWS zone time-of-day = hour ":" minute [ ":" second ] hour = 2DIGIT / obs-hour minute = 2DIGIT / obs-minute second = 2DIGIT / obs-second zone = (( "+" / "-" ) 4DIGIT) / obs-zone Resnick Standards Track [Page 14] RFC 2822 Internet Message Format April 2001
 The day is the numeric day of the month.  The year is any numeric
 year 1900 or later.
 The time-of-day specifies the number of hours, minutes, and
 optionally seconds since midnight of the date indicated.
 The date and time-of-day SHOULD express local time.
 The zone specifies the offset from Coordinated Universal Time (UTC,
 formerly referred to as "Greenwich Mean Time") that the date and
 time-of-day represent.  The "+" or "-" indicates whether the
 time-of-day is ahead of (i.e., east of) or behind (i.e., west of)
 Universal Time.  The first two digits indicate the number of hours
 difference from Universal Time, and the last two digits indicate the
 number of minutes difference from Universal Time.  (Hence, +hhmm
 means +(hh * 60 + mm) minutes, and -hhmm means -(hh * 60 + mm)
 minutes).  The form "+0000" SHOULD be used to indicate a time zone at
 Universal Time.  Though "-0000" also indicates Universal Time, it is
 used to indicate that the time was generated on a system that may be
 in a local time zone other than Universal Time and therefore
 indicates that the date-time contains no information about the local
 time zone.
 A date-time specification MUST be semantically valid.  That is, the
 day-of-the-week (if included) MUST be the day implied by the date,
 the numeric day-of-month MUST be between 1 and the number of days
 allowed for the specified month (in the specified year), the
 time-of-day MUST be in the range 00:00:00 through 23:59:60 (the
 number of seconds allowing for a leap second; see [STD12]), and the
 zone MUST be within the range -9959 through +9959.
3.4. Address Specification
 Addresses occur in several message header fields to indicate senders
 and recipients of messages.  An address may either be an individual
 mailbox, or a group of mailboxes.
address = mailbox / group mailbox = name-addr / addr-spec name-addr = [display-name] angle-addr angle-addr = [CFWS] "<" addr-spec ">" [CFWS] / obs-angle-addr group = display-name ":" [mailbox-list / CFWS] ";"
                      [CFWS]
Resnick Standards Track [Page 15] RFC 2822 Internet Message Format April 2001 display-name = phrase mailbox-list = (mailbox *("," mailbox
/data/webs/external/dokuwiki/data/pages/rfc/rfc2822.txt · Last modified: 2001/04/18 15:43 by 127.0.0.1

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