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rfc:rfc987

UCL Technical Report 120 Mailgroup Note 19

Network Working Group S.E. Kille Request for Comments: 987 University College London

                                                             June 1986
                 Mapping between X.400 and RFC 822

Status of This Memo

 This RFC suggests a proposed protocol for the ARPA-Internet
 community, and requests discussion and suggestions for improvements.
 Distribution of this memo is unlimited.
 This document describes a set of mappings which will enable
 interworking between systems operating the CCITT X.400 (1984) series
 of protocols [CCITT84a], and systems using the RFC 822 mail protocol
 [Crocker82a], or protocols derived from RFC 822.  The approach aims
 to maximise the services offered across the boundary, whilst not
 requiring unduly complex mappings.  The mappings should not require
 any changes to end systems.
 This specification should be used when this mapping is performed on
 the ARPA-Internet or in the UK Academic Community.  This
 specification may be modified in the light of implementation
 experience, but no substantial changes are expected.

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RFC 987 June 1986 Mapping between X.400 and RFC 822

Chapter 1 – Overview

 1.1.  X.400
    The X.400 series protocols have been defined by CCITT to provide
    an Interpersonal Messaging Service (IPMS), making use of a store
    and forward Message Transfer Service.  It is expected that this
    standard will be implemented very widely.  As well as the base
    standard (X.400), work is underway on various functional standards
    of profiles which specify how X.400 will be used in various
    communities.  Many of the major functional standards (e.g. from
    CEPT, CEN/CENELEC, and NBS) are likely to be similar.  Some of the
    decisions in this document are in the light of this work.  No
    reference is given, as these documents are not currently stable.
 1.2.  RFC 822
    RFC 822 evolved as a messaging standard on the DARPA (the US
    Defense Advanced Research Projects Agency) Internet.  It is
    currently used on the ARPA-Internet in conjunction with two other
    standards: RFC 821, also known as Simple Mail Transfer Protocol
    (SMTP) [Postel82a], and RFC 920 which is a specification for a
    domain name system and a distributed name service [Postel84a].
    RFC 822, or protocols derived from RFC 822 are used in a number of
    other networks.  In particular:
       UUCP Networks
          UUCP is the UNIX to UNIX CoPy protocol <0>, which is usually
          used over dialup telephone networks to provide a simple
          message transfer mechanism.  There are some extensions to
          RFC 822, particularly in the addressing.  They are likely to
          use domains which conform to RFC 920, but not the
          corresponding domain nameservers [Horton86a].
       CSNET
          Some portions of CSNET will follow the ARPA-Internet
          protocols. The dialup portion of CSNET uses the Phonenet
          protocols as a replacement for RFC 821.  This portion is
          likely to use domains which conform to RFC 920, but not the
          corresponding domain nameservers.
       BITNET
          Some parts of BITNET use RFC 822 related protocols, with
          EBCDIC encoding.

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       JNT Mail Networks
          A number of X.25 networks, particularly those associated
          with the UK Academic Community, use the JNT (Joint Network
          Team) Mail Protocol, also known as Greybook [Kille84a].
          This is used with domains and name service specified by the
          JNT NRS (Name Registration Scheme) [Larmouth83a].
    The mappings specified here are appropriate for all of these
    networks.
 1.3.  The Need for Conversion
    There is a large community using RFC 822 based protocols for mail
    services, who will wish to communicate with X.400 systems.  This
    will be a requirement, even in cases where communities intend to
    make a transition to use of X.400, where conversion will be needed
    to ensure a smooth service transition.  It is expected that there
    will be more than one gateway <1>, and this specification will
    enable them to behave in a consistent manner.  These gateways are
    sometimes called mail relays.  Consistency between gateways is
    desirable to provide:
       1.   Consistent service to users.
       2.   The best service in cases where a message passes through
            multiple gateways.
 1.4.  General Approach
    There are a number of basic principles underlying the details of
    the specification.
       1.   The specification should be pragmatic.  There should not
            be a requirement for complex mappings for 'Academic'
            reasons.  Complex mappings should not be required to
            support trivial additional functionality.
       2.   Subject to 1), functionality across a gateway should be as
            high as possible.
       3.   It is always a bad idea to lose information as a result of
            any transformation.  Hence, it is a bad idea for a gateway
            to discard information in the objects it processes.  This
            includes requested services which cannot be fully mapped.
       4.   All mail gateways actually operate at exactly one level

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RFC 987 June 1986 Mapping between X.400 and RFC 822

            above the layer on which they conceptually operate.  This
            implies that the gateway must not only be cognisant of the
            semantics of objects at the gateway level, but also be
            cognisant of higher level semantics.  If meaningful
            transformation of the objects that the gateway operates on
            is to occur, then the gateway needs to understand more
            than the objects themselves.
 1.5.  Gatewaying Model
    1.5.1.  X.400
       The CCITT X.400 series recommendations specify a number of
       services and protocols.  The services are specified in X.400.
       Two of these services are fundamental to this document:
          1.   The Message Transfer Service, which can be provided by
               either the P1 or P3 protocols, which are  specified in
               X.411 [CCITT84b]. This document talks in terms of P1,
               but the mappings are equally applicable to P3.
          2.   The Interpersonal Messaging Service (IPMS), which is
               provided by the P2 protocol specified in X.420
               [CCITT84c].
       This document considers only IPMS, and not of any other usage
       of the Message Transfer Service.  This is reasonable, as
       RFC 822, broadly speaking, provides a service corresponding to
       IPMS, and no services other than IPMS have been defined over
       the Message Transfer Service. As none of the RTS (Reliable
       Transfer Service) service elements is available to the IPMS
       user, this level and lower levels are of no concern in this
       gatewaying specification.  Note that in this memo "IP" means
       "InterPersonal" (not Internet Protocol).
       The Message Transfer Service defines an end-to-end service over
       a series of Message Transfer Agents (MTA).  It also defines a
       protocol, P1, which is used between a pair of MTAs.  This
       protocol is simply a file format (Message Protocol Data Unit,
       or MPDU), transferred between two MTAs using the RTS.  There
       are three types of MPDU:
          User MPDU
             This contains envelope information, and uninterpreted
             contents. The envelope includes an ID, an originator, a

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             list of recipients, and trace information.  It is used to
             carry data for higher level services.
          Probe
             This contains only envelope information.  It is used to
             determine whether a User UMPDU could be delivered to a
             given O/R (originator/recipient) name.
          Delivery Report
             This contains envelope information, and specified
             contents.  It is used to indicate delivery success or
             failure of a User or Probe MPDU over the Message Transfer
             Service.
       IPMS (P2) specifies two content types for the P1 User MPDU
       (User Agent Protocol Data Units or UAPDU):
          Interpersonal Message (IM-UAPDU)
             This has two components: a heading, and a body.  The body
             is structured as a sequence of body parts, which may be
             basic components (e.g.IA5 text, or G3 fax), or IP
             Messages.  The header contains end to end user
             information, such as subject, primary recipients (To:),
             and priority.  The validity of these fields is not
             guaranteed by the Message Transfer Service.  This
             provides the basic IPMS.
          Status Report (SR-UAPDU)
             This UAPDU has defined contents.  It is used to indicate
             that a message has been received by a User Agent.  It
             does not have to be implemented.
    1.5.2.  RFC 822
       RFC 822 is based on the assumption that there is an underlying
       service, which is here called the 822-P1 service.  The 822-P1
       service provides three basic functions:
          1.   Identification of a list of recipients.
          2.   Identification of an error return address.
          3.   Transfer of an RFC 822 message.

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       It is possible to achieve 2) within the RFC 822 header.  Some
       822-P1 protocols, in particular SMTP, can provide additional
       functionality, but as these are neither mandatory in SMTP, nor
       available in other 822-P1 protocols, they are not considered
       here.  Details of aspects specific to a number of 822-P1
       protocols are given in appendices B to E.  An RFC 822 message
       consists of a header, and content which is uninterpreted ASCII
       text.  The header is divided into fields, which are the
       protocol elements.  Most of these fields are analogous to P2
       header elements, although some are analogous to P1 envelope
       elements.
    1.5.3.  The Gateway
       Given this functional description of the two protocols, the
       functional nature of a gateway can now be considered.  It would
       be elegant to consider the 822-P1 service mapping onto P1 and
       RFC 822 mapping onto P2, but reality just does not fit.
       Therefore one must consider that P1 or P1 + P2 on one side are
       mapped into RFC 822 + 822-P1 on the other in a slightly tangled
       manner.  The details of the tangle will be made clear in
       chapter 5.  The following basic mappings are thus proposed.
       When going from RFC 822 to X.400, an RFC 822 message and the
       associated 822-P1 information is always mapped into an IM-UAPDU
       and the associated P1 envelope.  Going from X.400 to RFC 822,
       an RFC 822 message and the associated 822-P1 information may be
       derived from:
          1.   A Delivery Report MPDU
          2.   An SR-UAPDU and the associated P1 envelope.
          3.   An IM-UAPDU and the associated P1 envelope.
       Probe MPDUs must be processed by the gateway - this is
       discussed in chapter 5.  Any other User MPDUs are not mapped by
       the gateway, and should be rejected at the gateway.

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 1.6.  Document Structure
    This document has five chapters:
       1.   Overview - this document.
       2.   Service Elements - This describes the (end user) services
            mapped by a gateway.
       3.   Basic mappings - This describes some basic notation used
            in chapters 3-5, the mappings between character sets, and
            some fundamental protocol elements.
       4.   Addressing - This considers the mapping between X.400 O/R
            names and RFC 822 addresses, which is a fundamental
            gateway component.
       5.   Protocol Elements - This describes the details of all
            other mappings.
    There are also six appendices:
       A.   Quoted String Encodings.
       B.   Mappings Specific to JNT Mail.
       C.   Mappings Specific to Internet Mail.
       D.   Mappings Specific to Phonenet Mail.
       E.   Mappings Specific to UUCP Mail.
       F.   Format of Address Tables.
 1.7.  Acknowledgements
    This document is eclectic, and credit should be given:
  1. Study of the EAN X.400 system code which performs this

function [Neufeld85a]. Some detailed clarification was

            made by the DFN report on EAN [Bonacker85a].
  1. An unpublished ICL report, which considered a subset of

the problem [ICL84a].

  1. A document by Marshall Rose [Rose85a].

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  1. A document by Mark Horton [Horton85a]. The string

encodings of chapter 3 were derived directly from this

            work, as is much of chapter 4.
  1. Discussion on a number of electronic mailing lists.
  1. Meetings in the UK and the US.

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RFC 987 June 1986 Mapping between X.400 and RFC 822

Chapter 2 – Service Elements

 RFC 822 and X.400 provide a number of services to the end user.  This
 document describes the extent to which each service can be supported
 across an X.400 <-> RFC 822 gateway.  The cases considered are single
 transfers across such a gateway, although the problems of multiple
 crossings are noted where appropriate.
 When a service element is described as supported, this means that
 when this service element is specified by a message originator for a
 recipient behind a gateway, that it is mapped by the gateway to
 provide the service implied by the element.  For example, if an
 RFC 822 originator specifies a Subject: field, this is considered to
 be supported, as an X.400 recipient will get a subject indication.
 Support implies:
  1. Semantic correspondence.
  1. No loss of information.
  1. Any actions required by the service element.
 For some services, the corresponding protocol elements map well, and
 so the service can be fully provided.  In other cases, the service
 cannot be provided, as there is a complete mismatch.  In the
 remaining cases, the service can be partially fulfilled.  The level
 of partial support is summarised.
    NOTE:  It should be clear that support of service elements on
    reception is not a gatewaying issue.  It is assumed that all
    outbound messages are fully conforming to the appropriate
    standards.
 2.1.  RFC 822
    RFC 822 does not explicitly define service elements, as distinct
    from protocol elements.  However, all of the RFC 822 header
    fields, with the exception of trace, can be regarded as
    corresponding to implicit RFC 822 service elements.  A mechanism
    of mapping used in several cases, is to place the text of the
    header into the body of the IP Message.  This can usually be
    regarded as partial support, as it allows the information to be
    conveyed to the end user even though there is no corresponding
    X.400 protocol element.  Support for the various service elements
    (headers) is now listed.

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       Date:
          Supported.
       From:
          Supported.  For messages where there is also a sender field,
          the mapping is to "Authorising Addresses", which has subtly
          different semantics to the general RFC 822 usage of From:.
       Sender:
          Supported.
       Reply-To:
          Supported.
       To:
          Supported.
       Cc:
          Supported.
       Bcc:
          Supported.
       Message-Id:
          Supported.
       In-Reply-To:
          Supported, for a single reference in msg-id form.  Other
          cases are passed in the message text.
       References:
          Supported.
       Keywords:
          Passed in the message text.

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       Subject:
          Supported.
       Comments:
          Passed in the message text.
       Encrypted:
          Passed in the message text.  This may not be very useful.
       Resent-*
          Passed in the message text.  In principle, these could be
          supported in a fuller manner, but this is not suggested.
       Other Fields
          In particular X-* fields, and "illegal" fields in common
          usage (e.g. "Fruit-of-the-day:") are passed in the message
          text.
 2.2.  X.400
    When mapping from X.400 to RFC 822, it is not proposed to map any
    elements into the body of an RFC 822 message.  Rather, new RFC 822
    headers are defined.  It is intended that these fields will be
    registered, and that co-operating RFC 822 systems may use them.
    Where these new fields are used, and no system action is implied,
    the service can be regarded as being almost supported.  Chapter 5
    describes how to map these new headers in both directions.  Other
    elements are provided, in part, by the gateway as they cannot be
    provided by RFC 822.  Some service elements are are marked N/A
    (not applicable).  These elements are only applicable to User
    Agent / Message Transfer Agent interaction and have no end-to-end
    implication. These elements do not need to be mapped by the
    gateway.
    2.2.1.  Message Transfer Service Elements
       Access Management
          N/A.

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       Content Type Indication
          Not mapped.  As it can only have one value (P2), there is
          little use in creating a new RFC 822 header field, unless it
          was to distinguish delivery reports.
       Converted Indication
          Supported by a new RFC 822 header.
       Delivery Time Stamp Indication
          N/A.
       Message Identification
          Supported, by use of a new RFC 822 header.  This new header
          is required, as X.400 has two message-ids whereas RFC 822
          has only one.
       Non-delivery Notification
          Not supported, although in general an RFC 822 system will
          return errors as IP messages.  In other elements, this
          pragmatic result is treated as effective support of this
          service element.
       Original Encoded Information Types Indication
          Supported as a new RFC 822 header.
       Registered Encoded Information Types
          N/A.
       Submission Time Stamp Indication
          Supported.
       Alternate Recipient Allowed
          Not supported.  Any value is ignored by the gateway.
       Deferred Delivery
          Support is optional.  The framework is provided so that
          messages may be held at the gateway.  However, a gateway

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          following this specification does not have to do this.  This
          is in line with the emerging functional standards.
       Deferred Delivery Cancellation
          Supported.
       Delivery Notification
          Supported at gateway.  Thus, a notification is sent by the
          gateway to the originator  <2>.
       Disclosure of Other Recipients
          Supported by use of a new RFC 822 header.
       Grade of Delivery Selection
          Supported as a new RFC 822 header.  In general, this will
          only be for user information in the RFC 822 world.
       Multi-Destination Delivery
          Supported.
       Prevention of Non-delivery Notification
          Not Supported, as there is no control in the RFC 822 world
          (but see Non-delivery Notification).
       Return of Contents
          This is normally the case, although the user has no control
          (but see Non-delivery Notification).
       Conversion Prohibition
          Supported.  Note that in practice this support is restricted
          by the nature of the gateway.
       Explicit Conversion
          Supported, for appropriate values (See the IPMS Typed Body
          service element).

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       Implicit Conversion
          Supported, in the sense that there will be implicit
          conversion to IA5 in cases where this is practical.
       Probe
          Supported at the gateway (i.e. the gateway services the
          probe).
       Alternate Recipient Assignment
          N/A.
       Hold for Delivery
          N/A.
    2.2.2.  Interpersonal Message Service Elements
       IP-message Identification
          Supported.
       Typed Body
          Supported.  IA5 is fully supported.  ForwardedIPMessage is
          supported, with some loss of information.  A subset of TTX
          is supported (see section 5 for the specification of this
          subset), with some loss of information.  SFD may be
          supported, with some loss of information.  TTX and SFD are
          only supported when conversion is allowed.  Other types are
          not supported.
       Blind Copy Recipient Indication
          Supported.
       Non-receipt Notification
          Not supported.
       Receipt Notification
          Not supported.

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       Auto-forwarded Indication
          Supported as new RFC 822 header.
       Originator Indication
          Supported.
       Authorising User's Indication
          Supported, although the mapping (From:) is not quite the
          same.
       Primary and Copy Recipients Indication
          Supported.
       Expiry Date Indication
          Supported as new RFC 822 header.  In general, only human
          action can be expected.
       Cross Referencing Indication
          Supported.
       Importance Indication
          Supported as new RFC 822 header.
       Obsoleting Indication
          Supported as new RFC 822 header.
       Sensitivity Indication
          Supported as new RFC 822 header.
       Subject Indication
          Supported.
       Reply Request Indication
          Supported as comment next to address.

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       Forwarded IP-message Indication
          Supported, with some loss of information.
       Body Part Encryption Indication
          Not supported.
       Multi-part Body
          Supported, with some loss of information, in that the
          structuring cannot be formalised in RFC 822.

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RFC 987 June 1986 Mapping between X.400 and RFC 822

Chapter 3 – Basic Mappings

 3.1.  Notation
    The P1 and P2 protocols are encoded in a structured manner
    according to the X.409 specifications, whereas RFC 822 is text
    encoded.  To define a detailed mapping, it is necessary to refer
    to detailed protocol elements in each format.  This is described.
    3.1.4.  RFC 822
       Structured text is defined according to the Extended Backus
       Naur Form (EBNF) defined in section 2 of RFC 822 [Crocker82a].
       In the EBNF definitions used in this specification, the syntax
       rules given in Appendix D of RFC 822 are assumed.  When these
       EBNF tokens are referred to outside an EBNF definition, they
       are identified by the string "882." appended to the beginning
       of the string (e.g. 822.addr-spec).  Additional syntax rules,
       to be used throughout this specification are defined in this
       chapter.
       The EBNF is used in two ways.
          1.   To describe components of RFC 822 messages (or of
               822-P1 components).  In this case, the lexical analysis
               defined in section 3 of RFC 822 should be used.  When
               these new EBNF tokens are referred to outside an EBNF
               definition, they are identified by the string "EBNF."
               appended to the beginning of the string (e.g.
               EBNF.bilateral-info).
          2.   To describe the structure of IA5 or ASCII information
               not in an RFC 822 message.  In these cases, tokens will
               either be self delimiting, or be delimited by self
               delimiting tokens.  Comments and LWSP are not used as
               delimiters.
    3.1.5.  X.409
       An element is referred to with the following syntax, defined in
       EBNF:
          element        = protocol "." definition *( "." definition )
          protocol       = "P1" / "P2"
          definition     = identifier / context
          identifier     = ALPHA *< ALPHA or DIGIT or "-" >
          context        = "[" 1*DIGIT "]"

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       For example, P2.Heading.subject defines the subject element of
       the P2 heading.  The same syntax is also used to refer to
       element values. For example,
       P1.EncodedInformationTypes.[0].g3Fax refers to a value of
       P1.EncodedInformationTypes.[0] .
 3.2.  ASCII and IA5
    A gateway will interpret all IA5 as ASCII.  Thus, they are treated
    identically for the rest of this document.
 3.3.  Universal Primitives
    There is a need to convert between ASCII text, and some of the
    Universal Primitive types defined in X.409 [CCITT84d].  For each
    case, an EBNF syntax definition is given, for use in all of this
    specification.  All EBNF syntax definitions of Universal
    Primitives are in lower case, whereas X.409 primitives are
    referred to with the first letter in upper case.  Except as noted,
    all mappings are symmetrical.
    3.3.1.  Boolean
       Boolean is encoded as:
          boolean = "TRUE" / "FALSE"
    3.3.2.  NumericString
       NumericString is encoded as:
          numericstring = *DIGIT
    3.3.3.  PrintableString
       PrintableString is a restricted IA5String defined as:
          printablestring  = *( ps-char / ps-delim )
          ps-char          = 1DIGIT /  1ALPHA / " " / "'" / "+" / ")"
                             / "," / "-" / "." / "/" / ":" / "=" / "?"
          ps-delim         = "("
       A structured subset of EBNF.printablestring is now defined.
       This can be used to encode ASCII in the PrintableString
       character set.

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          ps-encoded       = *( ps-char / ps-encoded-char )
          ps-encoded-char  =   "(a)"               ; (@)
                             / "(p)"               ; (%)
                             / "(b)"               ; (!)
                             / "(q)"               ; (")
                             / "(u)"               ; (_)
                             / "(" 3DIGIT ")"
       The 822.3DIGIT in EBNF.ps-encoded-char must have range 0-127
       (Decimal), and is interpreted in decimal as the corresponding
       ASCII character. Special encodings are given for: at sign (@),
       percent (%), exclamation mark/bang (!), double quote ("), and
       underscore (_).  These characters are not included in
       PrintableString, but are common in RFC 822 addresses.  The
       abbreviations will ease specification of RFC 822 addresses from
       an X.400 system.
       An asymmetric mapping between PrintableString and ASCII can now
       be defined <3>.  To encode ASCII as PrintableString, the
       EBNF.ps-encoded syntax is used, with all EBNF.ps-char AND
       EBNF.ps-delim mapped directly <4>.  All other 822.CHAR are
       encoded as EBNF.ps-encoded-char. There are two cases of
       encoding PrintableString as ASCII.  If the PrintableString can
       be parsed as EBNF.ps-encoded, then the previous mapping should
       be reversed.  If not, it should be interpreted as
       EBNF.printablestring.
       Some examples are now given.  Note the arrows which indicate
       asymmetrical mappings:
          PrintableString           ASCII
          'a demo.'         <->   'a demo.'
          foo(a)bar         <->   foo@bar
          (q)(u)(p)(q)      <->   "_%"
          (a)               <->   @
          (a)               <-    (a)
          (040)a(041)       ->    (a)
          (040)(a)          ->    (@
          ((a)              <-    (@
       The algorithm is designed so that it is simple to use in all
       common cases, so that it is general, and so that it is
       straightforward to code.  It is not attempting to minimise the
       number of pathological cases.

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    3.3.4.  T.61String
       T.61 strings are, in general, only used for conveying human
       interpreted information.  Thus, the aim of a mapping should be
       to render the characters appropriately in the remote character
       set, rather than to maximise reversibility.  The mappings
       defined in the CEN/CENELEC X.400 functional standard should be
       used [CEN/CENELEC/85a].  These are based on the mappings of
       X.408 (sections 4.2.2 and 5.2.2).
    3.3.5.  UTCTime
       Both UTCTime and the RFC 822 822.date-time syntax contain: Year
       (lowest two digits), Month, Day of Month, hour, minute, second
       (optional), and Timezone.  822.date-time also contains an
       optional day of the week, but this is redundant.  Therefore a
       symmetrical mapping can be made between these constructs <5>.
       The UTCTime format which specifies the timezone offset should
       be used, in line with CEN/CENELEC recommendations.

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Chapter 4 – Addressing

 Addressing is probably the trickiest problem of an X.400 <-> RFC 822
 gateway.  Therefore it is given a separate chapter.  This chapter, as
 a side effect, also defines a standard textual representation of
 X.400 addresses.
 Initially we consider an address in the (human) mail user sense of
 "what is typed at the mailsystem to reference a human".  A basic
 RFC 822 address is defined by the EBNF EBNF.822-address:
    822-address     = [ route ] addr-spec
 In an 822-P1 protocol, the originator and each recipient should be
 considered to be defined by such a construct.  In an RFC 822 header,
 the EBNF.822-address is encapsulated in the 822.address syntax rule,
 and there may also be associated comments.  None of this extra
 information has any semantics, other than to the end user.
 The basic X.400 address is defined by P1.ORName.  In P1 all recipient
 P1.ORnames are encapsulated within P1.RecipientInfo, and in P2 all
 P2.ORNames <6> are encapsulated within P2.ORDescriptor.
 It can be seen that RFC 822 822.address must be mapped with
 P2.ORDescriptor, and that RFC 822 EBNF.822-address must be mapped
 with P1.ORName (originator) and P1.RecipientInfo (recipients).
 This chapter is structured as follows:
    4.1  Introduction.
    4.2  A textual representation of P1.ORName.  This is needed for
         the later mappings, and as a side effect provides a standard
         representation for O/R names.
    4.3  Mapping between EBNF.822-address and P1.ORName
    4.4  The Full P1 / 822-P1 Mapping
    4.5  The Full P2 / RFC 822 Mapping
    4.6  Mapping Message-IDs.

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 4.1.  A textual representation of P1.ORName.
    P1.ORName is structured as a set of attribute value pairs.  It is
    clearly necessary to be able to encode this in ASCII for
    gatewaying purposes.  A general encoding is given here, which may
    be used as a basis for a user interface, as well as for the
    defined gateway mapping.
    4.1.1.  Basic Representation
       A series of BNF definitions of each possible attribute value
       pair is given, which is given a 1:1 mapping with the X.400
       encoding.  The rest of the mapping then talks in terms of these
       BNF components, with the mapping to X.400 encoding being
       trivial.
       attributevalue = c / admd / prmd / x121 / t-id / o / ou
                       / ua-id / pn.g / pn.i / pn.s / pn.gq / dd.value
       c        = printablestring       ; P1.CountryName
       admd     = printablestring       ; P1.AdministrationDomainName
       prmd     = printablestring       ; P1.PrivateDomainName
       x121     = numericstring         ; P1.X121Address
       t-id     = numericstring         ; P1.TerminalID
       o        = printablestring       ; P1.OrganisationName
       ou       = printablestring       ; P1.OrganisationalUnit
       ua-id    = numericstring         ; P1.UniqueUAIdentifier
       pn.s     = printablestring       ; P1.PersonalName.surName
       pn.g     = printablestring       ; P1.PersonalName.givenName
       pn.i     = printablestring       ; P1.PersonalName.initials
       pn.gq    = printablestring       ; P1.PersonalName.generation
                                          Qualifier
       dd.value = printablestring       ; P1.DomainDefined
                                          Attribute.value
       In cases where an attribute can be encoded as either a
       PrintableString or NumericString (Country, ADMD, PRMD) it is
       assumed that the NumericString encoding will be adopted if
       possible.  This prevents the encoding of PrintableString where
       the characters are all numbers. This restriction seems
       preferable to the added complexity of a general solution.
       Similarly, we can define a set of attribute types.

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       dd.type = printablestring      ; P1.DomainDefinedAttribute.type
       standard-type =
                 "C"           ; P1.CountryName
               / "ADMD"        ; P1.AdministrationDomainName
               / "PRMD"        ; P1.PrivateDomainName
               / "X121"        ; P1.X121Address
               / "T-ID"        ; P1.TerminalID
               / "O"           ; P1.OrganisationName
               / "OU"          ; P1.OrganisationalUnit
               / "UA-ID"       ; P1.UniqueUAIdentifier
               / "S"           ; P1.PersonalName.surName
               / "G"           ; P1.PersonalName.givenName
               / "I"           ; P1.PersonalName.initials
               / "GQ"          ; P1.PersonalName.generationQualifier
       standard-dd-type =
                 "RFC-822"     ; dd.type = "RFC-822"
               / "JNT-Mail"    ; dd.type = "JNT-Mail"
               / "UUCP"        ; dd.type = "UUCP"
    4.1.2.  Encoding of Personal Name
       Handling of Personal Name based purely on the
       EBNF.standard-type syntax defined above is likely to be clumsy.
       It seems desirable to utilise the "human" conventions for
       encoding these components.  A syntax is proposed here.  It is
       designed to cope with the common cases of O/R Name
       specification where:
          1.   There is no generational qualifier
          2.   Initials contain only letters <7>.
          3.   Given Name does not contain full stop ("."), and is at
               least two characters long.
          4.   If Surname contains full stop, then it may not be in
               the first two characters, and either initials or given
               name is present.

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       The following EBNF is defined:
          encoded-pn      = [ given "." ] *( initial "." ) surname
          given           = 2*<ps-char not including ".">
          initial         = ALPHA
          surname         = printablestring
       Subject to the above restriction, this is a reversible mapping.
       For example:
          GivenName       = "Marshall"
          Surname         = "Rose"
          Maps with  "Marshall.Rose"
          Initials        = "MT"
          Surname         = "Rose"
          Maps with  "M.T.Rose"
          GivenName       = "Marshall"
          Initials        = "MT"
          Surname         = "Rose"
          Maps with  "Marshall.M.T.Rose"
       Note that CCITT guidelines suggest that Initials is used to
       encode ALL initials.  Therefore, the proposed encoding is
       "natural" when either GivenName or Initials, but not both, are
       present.  The case where both are present can be encoded, but
       this appears to be contrived!
    4.1.3.  Two encodings of P1.ORName
       Given this structure, we can specify a BNF representation of an
       O/R Name.

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          std-orname      = 1*( "/" attribute "=" value ) "/"
          attribute       = standard-type
                          / "PN"
                          / standard-dd-type
                          / registered-dd-type
                          / "DD." std-printablestring
          value           = std-printablestring
          registered-dd-type
                          = std-printablestring
          std-printablestring =
                          = *( std-char / std-pair )
          std-char        = <ps-delim, and any ps-char except "/"
                            and "=">
          std-pair        = "$" ( ps-delim / ps-char )
       If the type is PN, the value is interpreted according to
       EBNF.encoded-pn, and the components of P1.PersonalName derived
       accordingly.  If the value is registered-dd-type, if the value
       is registered at the SRI NIC as an accepted Domain Defined
       Attribute type, then the value should be interpreted
       accordingly.  This restriction maximises the syntax checking
       which can be done at a gateway.
       Another syntax is now defined.  This is intended to be
       compatible with the syntax used for 822.domains.  This syntax
       is not intended to be handled by users.
          dmn-orname      = dmn-part *( "." dmn-part )
          dmn-part        = attribute "$" value
          attribute       = standard-type
                          / "~" dmn-printablestring
          value           = dmn-printablestring
          dmn-printablestring =
                          = *( dmn-char / dmn-pair )
          dmn-char        = <ps-delim, and any ps-char except ".">
          dmn-pair        = "\."
       For example: C$US.ADMD$ATT.~ROLE$Big\.Chief

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 4.2.  Mapping between EBNF.822-address and P1.ORName
    Ideally, the mapping specified would be entirely symmetrical and
    global, to enable addresses to be referred to transparently in the
    remote system, with the choice of gateway being left to the
    Message Transfer Service.  There are two fundamental reasons why
    this is not possible:
       1.   The syntaxes are sufficiently different to make this
            awkward.
       2.   In the general case, there would not be the necessary
            administrative co-operation between the X.400 and RFC 822
            worlds, which would be needed for this to work.
    Therefore, an asymmetrical mapping is defined.
    4.2.1.  X.400 encoded in RFC 822
       The std-orname syntax is  used to encode O/R Name information
       in the 822.local-part of EBNF.822-address.  Further  O/R Name
       information may be associated with the 822.domain component.
       This cannot be used in the general case, basically due to
       character set problems, and lack of order in X.400 O/R Names.
       The only way to encode the full PrintableString character set
       in a domain is by use of the 822.domain-ref syntax.  This is
       likely to cause problems on many systems.  The effective
       character set of domains is in practice reduced from the
       RFC 822 set, by restrictions imposed by domain conventions and
       policy.
       A generic 822.address consists of a 822.local-part and a
       sequence of 822.domains (e.g.
       <@domain1,@domain2:user@domain3>).  All except the 822.domain
       associated with the 822.local-part (domain3 in this case)
       should be considered to specify routing within the RFC 822
       world, and will not be interpreted by the gateway (although
       they may have identified the gateway from within the RFC 822
       world).  The 822.domain associated with the 822.local-part may
       also identify the gateway from within the RFC 822 world.  This
       final 822.domain may be used to determine some number of O/R
       Name attributes.  The following O/R Name attributes are
       considered as a hierarchy, and may be specified by the domain.
       They are (in order of hierarchy):
          Country, ADMD, PRMD, Organisation, Organisational Unit

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       There may be multiple Organisational Units.
       Associations may be defined between domain specifications, and
       some set of attributes.  This association proceeds
       hierarchically: i.e. if a domain implies ADMD, it also implies
       country.  If one of the hierarchical components is omitted from
       an X.400 structure, this information can be associated with the
       corresponding domain (e.g. a domain can be mapped onto a
       Country/ADMD/Organisation tuple). Subdomains under this are
       associated according to the O/R Name hierarchy.  For example:
          => "AC.UK" might be associated with
                                        C="234", ADMD="BT", PRMD="DES"
          then domain "R-D.Salford.AC.UK" maps with
                 C="234", ADMD="BT", PRMD="DES", O="Salford", OU="R-D"
       There are two basic reasons why a domain/attribute mapping
       might be maintained, as opposed to using simply subdomains:
          1.   As a shorthand to avoid redundant X.400 information.
               In particular, there will often be only one ADMD per
               country, and so it does not need to be given
               explicitly.
          2.   To deal with cases where attribute values do not fit
               the syntax:
             domain-syntax   = ALPHA [ *alphanumhyphen alphanum ]
             alphanum        = <ALPHA or DIGIT>
             alphanumhyphen  = <ALPHA or DIGIT or HYPHEN>
       Although RFC 822 allows for a more general syntax, this
       restriced syntax is chosen as it is the one chosen by the
       various domain service administrations.
       This provides a general aliasing mechanism.
       This set of mappings need only be known by the gateways
       relaying between the RFC 822 world, and the O/R Name namespace
       associated with the mapping in question.  However, it is
       desirable (for the optimal mapping of third party addresses)
       for all gateways to know these mappings.  A format for the
       exchange of this information is defined in Appendix F.
       From the standpoint of the RFC 822 Message Transfer System, the
       domain specification is simply used to route the message in the

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       standard manner.  The standard domain mechanisms are used to
       identify gateways, and are used to select appropriate gateways
       for the corresponding O/R Name namespace.  In most cases, this
       will be done by registering the higher levels, and assuming
       that the gateway can handle the lower levels.
       As a further mechanism to simplify the encoding of common
       cases, where the only attributes to be encoded on the LHS are
       Personal Name attributes which comply with the restrictions of
       4.2.2, the 822.local-part may be encoded as EBNF.encoded-pn.
       An example encoding is:
          /PN=J.Linnimouth/GQ=5/@Marketing.Xerox.COM
          encodes the P1.ORName consisting of
             P1.CountryName                  = "US"
             P1.AdministrationDomainName     = "ATT"
             P1.OrganisationName             = "Xerox"
             P1.OrganisationalUnit           = "Marketing"
             P1.PersonalName.surName         = "Linnimouth"
             P1.PersonalName.initials        = "J"
             P1.PersonalName.GenerationQualifier = "5"
          If the GenerationQualifier was not present, the encoding
          J.Linnimouth@Marketing.Xerox.COM could be used.
       Note that in this example, the first three attributes are
       determined by the domain Xerox.COM.  The OrganisationalUnit is
       determined systematically.
       There has been an implicit assumption that an RFC 822 domain is
       either X.400 or RFC 822.  This is pragmatic, but undesirable,
       as the namespace should be structured on a logical basis which
       does not necessarily correspond to the choice of Message
       Transfer protocols. The restriction can be lifted, provided
       that the nameservice deals with multiple message transfer
       protocols.  This can happen in a straightforward manner for the
       UK NRS, as explained in [Kille86a].  It could also be achieved
       with the DARPA Domain Nameserver scheme by use of the WKS
       mechanism.

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    4.2.2.  RFC 822 Encoded in X.400
       In some cases, the encoding defined above may be reversed, to
       give a "natural" encoding of genuine RFC 822 addresses.  This
       depends largely on the allocation of appropriate management
       domains.
       The general case is mapped by use of domain defined attributes.
       Three are defined, according to the full environment used to
       interpret the RFC 822 information.
          1.   Domain defined type "RFC-822".  This string is to be
               interpreted in the context of RFC 822, and RFC 920
               [Crocker82a,Postel84a].
          2.   Domain defined type "JNT-Mail".  This string is to be
               interpreted in the context of the JNT Mail protocol,
               and the NRS [Kille84a,Larmouth83a].
          3.   Domain defined type "UUCP".  This is interpreted
               according to the constraints of the UUCP world
               [Horton86a].
       These three are values currently known to be of use.  Further
       recognised values may be defined.  These will be maintained in
       a list at the SRI Network Information Center.
       Other O/R Name attributes will be used to identify a context in
       which the O/R Name will be interpreted.  This might be a
       Management Domain, or some part of a Management Domain which
       identifies a gateway MTA.  For example:
          1)
          C               = "GB"
          ADMD            = "BT"
          PRMD            = "AC"
          "JNT-Mail"      = "Jimmy(a)UK.CO.BT-RESEARCH-LABS"
          2)
          C               = "US"
          ADMD            = "Telemail"
          PRMD            = "San Fransisco"
          O               = "U Cal"
          OU              = "Berkeley"
          "RFC-822"       = "postel(a)usc-isib.arpa"

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       Note in each case the PrintableString encoding of "@" as "(a)".
       In the first example, the "JNT-Mail" domain defined attribute
       is interpreted everywhere within the (Administrative or
       Private) Management Domain.  In the second example, further
       attributes are needed within the Management Domain to identify
       a gateway.  Thus, this scheme can be used with varying levels
       of Management Domain co-operation.
    4.2.3.  RFC 822 -> X.400
       There are two basic cases:
          1.   X.400 addresses encoded in RFC 822.  This will also
               include RFC 822 addresses which are given reversible
               encodings.
          2.   "Genuine" RFC 822 addresses.
       The mapping should proceed as follows, by first assuming case
       1).
       STAGE 1.
          1.   If the 822-address is not of the form:
             local-part "@" domain
             go to stage 2.
          2.   Attempt to parse domain as:
  • ( domain-syntax "." ) known-domain
             Where known-domain is the longest possible match in a
             list of gatewayed domains.  If this fails, and the domain
             does not explicitly identify the local gateway, go to
             stage 2.  If it succeeds, allocate the attributes
             associated with EBNF.known-domain, and systematically
             allocate the attributes implied by each
             EBNF.domain-syntax component.
          3.   Map 822.local-part to ASCII, according to the
               definition of Appendix A.  This step should be applied:
             A.  If the source network cannot support
                 822.quoted-string (as discussed in Appendix A).

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             B.  If the address is an 822-P1 recipient.
                This mapping is always applied in case B, as it
                increases the functionality of the gateway, and does
                not imply any loss of generality.  Mapping case B
                allows sites which cannot generate 822.quoted-string
                to address recipients the gateway, without the gateway
                having to know this explicitly.  There is no loss of
                functionality, as the quoting character of Appendix A
                (#) is not in PrintableString.  This seems desirable.
                It should not be applied in to other addresses, as a
                third party RFC#822 address containing the sequence
                EBNF.atom-encoded (as defined in Appendix A) would be
                transformed asymmetrically.
          4.   Map the result of 3) to EBNF.ps-encoded according to
               section 3.
          5.   Parse the result of 4) according to the EBNF
               EBNF.std-orname.  If this parse fails, parse the result
               of 4) according to the EBNF EBNF.encoded-pn.  If this
               also fails, go to stage 2.  Otherwise, the result is a
               set of type/value pairs.
          6.   Associate the EBNF.attribute-value syntax (determined
               from the identified type) with each value, and check
               that it conforms.  If not, go to stage 2.
          7.   Ensure that the set of attributes conforms both to the
               X.411 P1.ORName specification and to the restrictions
               on this set given in X.400.  If not go to stage 2.
          8.   Build the O/R Name from this information.
       STAGE 2.
       This will only be reached if the RFC 822 EBNF.822-address is
       not a valid X.400 encoding.  If the address is an 822-P1
       recipient address, it must be rejected, as there is a need to
       interpret such an address in X.400.  For the 822-P1 return
       address, and any addresses in the RFC 822 header, they should
       now be encoded as RFC 822 addresses in an X.400 O/R Name:
          1.   Convert the EBNF.822-address to PrintableString, as
               specified in chapter 3.
          2.   The domain defined attribute ("RFC-822", "JNT-Mail" or

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               "UUCP") appropriate to the gateway should be selected,
               and its value set.
          3.   Build the rest of the O/R Name in the local Management
               Domain agreed manner, so that the O/R Name will receive
               a correct global interpretation.
    4.2.4.  X.400 -> RFC 822
       There are two basic cases:
          1.   RFC 822 addresses encoded in X.400.
          2.   "Genuine" X.400 addresses.  This may include
               symmetrically encoded RFC 822 addresses.
       When a P1 Recipient O/R Name is interpreted, gatewaying will be
       selected if there a single special domain defined attribute
       present ("RFC-822", "JNT-Mail" or "UUCP").  In this case, use
       mapping A.  For other O/R Names which
          1.   Contain the special attribute.
             AND
          2.   Identify the local gateway with the other attributes.
       Use mapping A.  In other cases, use mapping B.
       Mapping A
          1.   Map the domain defined attribute value to ASCII, as
               defined in chapter 3.
          2.   Where appropriate (P1 recipients), interpret the string
               according to the semantics implied by the domain
               defined attribute.
       Mapping B.
       This will be used for X.400 addresses which do not use the
       explicit RFC 822 encoding.
          1.   Noting the hierarchy specified in 4.3.1, determine the
               maximum set of attributes which have an associated
               domain specification. If no match is found, allocate

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               the domain as the domain specification of the local
               gateway, and go to step 4.
          2.   Following the 4.3.1 hierarchy, if each successive
               component exists, and conforms to the syntax
               EBNF.domain-syntax (as defined in 4.3.1), allocate the
               next subdomain.
          3.   If the remaining components are personal-name
               components, conforming to the restrictions of 4.2.2,
               then EBNF.encoded-pn should be derived to form
               822.local-part.  In other cases the remaining
               components should simply be encoded as a 822.local-part
               using the EBNF.std-orname syntax.  Where registered
               domain defined types exist, the DD. syntax should not
               be used.
          4.   If this step is reached for an 822-P1 recipient, then
               the address is invalid.  For other addresses, if the
               derived 822.local-part can only be encoded by use of
               822.quoted-string, the gateway may optionally use the
               ASCII to 822.local-part mapping defined in Appendix A,
               dependent on the mail protocols of the networks being
               relayed to.  Use of this encoding is discouraged.
 4.3.  Repeated Mappings
    The mappings defined are symmetrical across a single gateway,
    except in certain pathological cases (see chapter 3).  However, it
    is always possible to specify any valid address across a gateway.
    This symmetry is particularly useful in cases of (mail exploder
    type) distribution list expansion.  For example, an X.400 user
    sends to a list on an RFC 822 system which he belongs to.  The
    received message will have the originator and any 3rd party X.400
    O/R names in correct format (rather than doubly encoded).  In
    cases (X.400 or RFC 822) where there is common agreement on
    gateway identification, then this will apply to multiple gateways.
    However, the syntax may be used to source route.
    For example:  X.400 -> RFC 822  -> X.400
       C               = "UK"
       ADMD            = "BT"
       PRMD            = "AC"
       "JNT-Mail"      = "/PN=Duval/DD.Title=Manager/(a)FR.PTT.Inria"

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       This will be sent to an arbitrary UK Academic Community gateway
       by X.400.  Then by JNT Mail to another gateway determined by
       the domain FR.PTT.Inria.  This will then derive the X.400 O/R
       Name:
          C               = "FR"
          ADMD            = "PTT"
          PRMD            = "Inria"
          PN.S            = "Duval"
          "Title"         = "Manager"
    Similarly:  RFC 822 -> X.400 -> RFC 822
       "/C=UK/ADMD=BT/PRMD=AC/RFC-822=jj(a)seismo.css.gov/"
                                                   @monet.berkeley.edu
       /C=UK/ADMD=BT/PRMD=AC/RFC-822=jj#l#a#r#seismo.css.gov/
                                                   @monet.berkeley.edu
       The second case uses the Appendix A encoding to avoid
       822.quoted-text. This will be sent to monet.berkeley.edu by
       RFC 822, then to the AC PRMD by X.400, and then to
       jj@seismo.css.gov by RFC 822.
 4.4.  The full P1 / 822-P1 mapping
    There are two basic mappings at the P1 level:
       1.   822-P1 return address <-> P1.UMPDUEnvelope.originator
       2.   822-P1 recipient <-> P1.RecipientInfo
    822-P1 recipients and return addresses are encoded as
    EBNF.822-address.  As P1.UMPDUEnvelope.originator is encoded as
    P1.ORName, mapping 1) has already been specified.
    P1.RecipientInfo contains a P1.ORName and additional information.
    The handling of this additional information is now specified.
    4.4.1.  RFC 822 -> X.400
       The following default settings should be made for each
       component of P1.RecipientInfo.
          P1.ExtensionIdentifier
             This can be set systematically by the X.400 system.

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          P1.RecipientInfo.perRecipientFlag
             Responsibility Flag should be set.  Report Request should
             be set according to content return policy, as discussed
             in section 5.3. User Report Request should be set to
             Basic.
          P1.ExplicitConversion
             This optional component should be omitted.
    4.4.2.  X.400 -> RFC 822
       The mapping only takes place in cases where
       P1.RecipientInfo.perRecipientFlag Responsibility Flag is set.
       The following treatment should be given to the other
       P1.RecipientInfo components.
          P1.ExtensionIdentifier
             Not used.
          P1.RecipientInfo.perRecipientFlag
             If ReportRequest is Confirmed or Audit-and-Confirmed then
             a delivery report indicating success should be sent by
             the gateway. This report should use each
             P1.ReportedRecipientInfo.SupplementaryInformation to
             indicate the identity of the gateway, and the nature of
             the report (i.e. only as far as the gateway).  Failures
             will be handled by returning RFC 822 messages, and so
             User Report Request set to No report is ignored.
          P1.ExplicitConversion
             If present, the O/R name should be rejected, unless the
             requested conversion can be achieved.  None of the
             currently recognised values of this parameter are
             appropriate to a gateway using this specification.

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 4.5.  The full P2 / RFC 822 mapping
    All RFC 822 addresses are assumed to use the 822.mailbox syntax.
    This should include all 822.comments associated with the lexical
    tokens of the 822.mailbox.  All P2.ORNames are encoded within the
    syntax P2.ORDescriptor, or P2.Recipient (or within Message IDs).
    An asymmetrical mapping is defined between these components.
    4.5.1.  RFC 822 -> X.400
       The following sequence is followed.
          1.   Take the address, and extract an EBNF.822-address.
               This can be derived trivially from either the
               822.addr-spec or 822.route-addr syntax.  This is mapped
               to P2.ORName as described above.
          2.   A string should be built consisting of (if present):
  1. The 822.phrase component if it is a 822.phrase

822.route-addr construct.

  1. Any 822.comments, in order, retaining the

parentheses.

                This string should then be encoded into T.61 (as
                described in chapter 3).  If the string is not null,
                it should be assigned to P2.ORDescriptor.freeformName.
          3.   P2.ORDescriptor.telephoneNumber should be omitted.
          4.   In cases of converting to P2.Recipient,
               P2.Recipient.replyRequest and
               P2.Recipient.reportRequest should be omitted.
       If the 822.group construct is present, each included
       822.mailbox should be encoded as above.  The 822.group should
       be mapped to T.61, and a P2.ORDesciptor with only a
       freeformName component built from it.
    4.5.2.  X.400 -> RFC 822
       In the basic case, where P2.ORName is present, proceed as
       follows.
          1.   Encode P2.ORName as EBNF.822-address.

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          2a.  If P2.ORDescriptor.freeformName is present, convert it
               to ASCII (chapter 3), and use use this as the
               822.phrase component of 822.mailbox using the
               822.phrase 822.route-addr construct.
          2b.  If P2.ORDescriptor.freeformName is absent, if
               EBNF.822-address is parsed as 822.addr-spec use this as
               the encoding of 822.mailbox. If EBNF.822-address is
               parsed as 822.route 822.addr-spec, then a 822.phrase
               taken from 822.local-part should be added.
          3.   If P2.ORDescriptor.telephoneNumber is present, this
               should be placed in a trailing 822.comment.
          4.   If P2.Recipient.reportRequest has the
               receiptNotification bit set, then an 822.comment
               "(Receipt Notification Requested)" should be appended
               to the address.  The effort of correlating P1 and P2
               information is too great to justify the gateway sending
               Receipt Notifications.
          5.   If P2.Recipient.replyRequest is present, an 822.comment
               "(Reply requested)" or "(Reply not requested)" should
               be appended to the address, dependent on its value.
       If P2.ORName is absent, P2.ORDescriptor.freeformName should be
       converted to ASCII, and used with the RFC 822 822.group syntax:
          freeformname ":" ";"
       Steps 3-5 should then be followed.
 4.6.  Message IDs
    There is a need to map both ways between 822.msg-id and
    P2.IPMessageID.  A mapping is defined which is symmetrical for
    non-pathological cases.  The mapping allows for the fact that
    P2.IPMessageID.PrintableString is mandatory for the Cen/Cenelec
    profile.  This allows for good things to happen when messages pass
    multiple times across the X.400/RFC 822 boundary.  A mapping
    between 822.msg-id and P1.MPDUIdentifier is defined.  This allows
    for X.400 error messages to reference an RFC 822 ID, which is
    preferable to a gateway generated ID.

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    4.6.1.  P2.IPMessageID -> 822.msg-id
       P2.IPMessageID.ORName is used to generate an 822.addr-spec, as
       defined above.  P2.IPMessageID.PrintableString is mapped to
       ASCII, as defined in chapter 3.  This string (if it is present
       and if the value is not "RFC-822") is appended to the front of
       the 822.local-part of the 822.msg-id, with "*" as a separator.
       If no ORName is present, an 822.msg-id of the form
       "PrintableString*@gateway-domain" is generated.
    4.6.2.  822.msg-id -> P2.IPMessageID
       822.local-part is parsed as:
          [ printablestring "*" ] real-local-part
       If EBNF.printablestring is found, it is mapped to
       PrintableString, and used as P2.IPMessageID.PrintableString.
       Otherwise
       P2.IPMessageID.PrintableString is set to "RFC-822".  This
       arbitrary value allows for conformance to Cen/Cenelec.  If
       EBNF.real-local-part is not present, no P2.IPMessageID.ORName
       is generated.  Otherwise,  822.local-part is replaced with
       EBNF.real-local-part, and 822.addr-spec is mapped to
       P2.IPMessageID.ORName as defined above.
    4.6.3.  822.msg-id -> P1.MPDUIdentifier
       P1.CountryName is assigned to "", P1.AdministrationDomainName
       to 822.domain (from 822.msg-id) and P1.MPDUIdentifier.IA5String
       to 822.local-part (from 822.msg-id).
    4.6.4.  P1.MPDUIdentifier -> 822.msg-id
       822.local-part is set to P1.MPDUIdentifier.IA5String, with any
       CRLF mapped to SPACE.  If P1.CountryName is "", 822.domain is
       set to P1.AdministrationDomainName; Otherwise to
       P1.AdministrationDomainName ".." P1.CountryName.  If there are
       any specials,  the domain literal encoding should be used.

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RFC 987 June 1986 Mapping between X.400 and RFC 822

Chapter 5 – Protocol Elements

 This chapter gives detailed mappings for the functions outlined in
 chapters 1 and 2.  It makes extensive use of the notations and
 mappings defined in chapters 3 and 4.  This chapter is structured as
 follows:
    5.1. Basic RFC 822 -> X.400 mappings
    5.2. A definition of some new RFC 822 elements, and their mapping
         to X.400.
    5.3  Some special handling associated with Return of Contents.
    5.4. X.400 -> RFC 822
 5.1.  RFC 822 -> X.400
    First, the basic functions of an 822-P1 protocol should be mapped
    as follows:
       822-P1 Originator
          Mapped to P1.UMPDUEnvelope.originator (see chapter 4).
       822-P1 Recipient
          Mapped to P1.RecipientInfo (see chapter 4).
    The RFC 822 headers are used to generate both a P1.UMPDUEnvelope
    and a P2.Heading.  The IP Message will have either one or two
    P2.BodyParts which will be type P2.IA5Text with no
    P2.IA5Text.repertoire component. The last P2.BodyPart will contain
    the RFC 822 message body.  If there are any RFC 822 headers which
    indicate mapping into the P2.BodyPart, then two P2.BodyParts are
    generated.  If a revised version of P2 allowed for extensible
    header specification, this would be seen as a preferable mapping.
    The first body part will start with the line:
       RFC-822-Headers:
    The rest of this body part will contain all of the headers not
    otherwise mapped (both 822.field-name and 822.field-body).  The
    order of any such headers should be preserved.  Similarly,
    ordering within P2.Heading and P1.UMPDUEnvelope should reflect
    ordering within the RFC 822 header.  No P1 or P2 optional fields
    are generated unless specified.

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    A pro-forma X.400 message is now specified.  Some of these
    defaults may be changed by the values in the RFC 822 message being
    mapped.  The mandatory P1 and P2 components have the following
    defaults.
       P1.MPDUIdentifier
          The default should be unique value generated by the gateway.
       P1.OriginatorORName
          Always generated from 822-P1.
       P1.ContentType
          P1.ContentType.p2
       P1.RecipientInfo
          These will always be supplied from 822-P1.
       P1.Trace
          The last P1.TraceInformation component is generated such
          that: P1.TraceInformation.GlobalDomainIdentifier is set to
          the local vaglue.  P1.DomainSuppliedInfo.action is set to
          relayed. P1.DomainSuppliedInfo.arrival is set to the current
          time. P1.DomainSuppliedInfo.previous may be set if there is
          anything sensible to set it to.
       P2.IPMessageID
          The default should be a unique value generated by the
          gateway.
    The following optional parameters should be set:
       P1.PerMessageFlag
          The P1.PerMessageFlag.contentReturnRequest bit should be set
          according to the discussion in section 5.3.  The
          P1.PerMessageFlag.alternateRecipientAllowed bit should be
          set, as it seems desirable to maximise opportunity for
          (reliable) delivery.

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RFC 987 June 1986 Mapping between X.400 and RFC 822

    The RFC 822 headings should be mapped as follows:
       Received:
          Fudged onto P1.TraceInformation (try not to grimace too
          much). P1.DomainSuppliedInfo.action is set to relayed.
          P1.DomainSuppliedInfo.arrival is set to the date-time
          component P1.TraceInformation.GlobalDomainIdentifier has
          P1.CountryName as a null string, and
          P1..AdministrationDomainName as the domain of the receiving
          host (if present - null string if not).
          P1.DomainSuppliedInfo.previous has P1.CountryName as a null
          string, and P1.AdministrationDomainName has the domain of
          the sending host with all other information enclosed in
          round parentheses.  The encoding of ASCII to PrintableString
          (chapter 3) should be used if needed.  For example:
             Received: from 44e.cs.ucl.ac.uk by vax2.Cs.Ucl.AC.UK
                            with SMTP  id a002110; 18 Dec 85 10:40 GMT
                maps to -
                P1.GlobalDomainIdentifier
                   CountryName                  = ""
                   AdministrationDomainName     = "vax2.Cs.Ucl.AC.UK"
                P1.DomainSuppliedInfo
                   arrival                      = 18 Dec 85 10:40 GMT
                   action                       = relayed
                   previous
                      CountryName               = ""
                      AdministrationDomainName  =
                             "44e.cs.ucl.ac.uk (with SMTP id a002110)"
       Date:
          This is used to set the first component of
          P1.TraceInformation. The mandatory components are set as
          follows:
             P1.GlobalDomainIdentifier
                CountryName                  = ""
                AdministrationDomainName     = ""
             P1.DomainSuppliedInfo
                arrival                      = time derived from Date:
                action                       = relayed
          No optional fields are used in the trace.

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       Message-Id:
          Mapped to P2.IPMessageID.  If the RFC 822 message does not
          contain a P1-Message-ID: field, the Message-Id: field is
          also mapped to P1.MPDUIdentifier.  For these, and all other
          fields containing msg-id the mappings of chapter 4 are used
          for each msg-id.
       From:
          If Sender: is present, this is mapped to
          P2.AuthorisingUsers.  If not, it is mapped to P2.Originator.
          For this, and other components containing addresses, the
          mappings of chapter 4 are used for each address.
       Sender:
          Mapped to P2.Originator.
       Reply-To:
          Mapped to P2.Heading.replyToUsers.
       To:
          Mapped to P2.Heading.primaryRecipients
       Cc:
          Mapped to P2.Heading.copyRecipients.
       Bcc:
          Mapped to P2.Heading.blindCopyRecipients.
       In-Reply-To:
          Mapped to P2.Heading.inReplyTo for the first (if any)
          822.msg-id component.  If the field contains an 822.phrase
          component, or there are multiple 822.msg-id components, the
          ENTIRE field is passed in the P2.BodyPart.
       References:
          Mapped to P2.Heading.crossReferences.

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RFC 987 June 1986 Mapping between X.400 and RFC 822

       Keywords:
          Passed in the P2.BodyPart.
       Subject:
          Mapped to P2.Heading.subject.  The field-body uses the
          mapping referenced in chapter 3 from ASCII to T.61.
       Comments:
          Passed in the P2.BodyPart.
       Encrypted:
          Passed in the P2.BodyPart.
       Resent-*
          Passed in the P2..BodyPart <8>.
       Other Fields
          In particular X-* fields, and "illegal" fields in common
          usage (e.g. "Fruit-of-the-day:") are passed in the
          P2.BodyPart.  The same treatment should be applied to
          RFC 822 fields where the content of the field does not
          conform to RFC 822 (e.g. a Date: field with unparsable
          syntax).
 5.2.  Extended RFC 822 Elements -> X.400
    First an EBNF definition of a number of extended fields is given,
    and then a mapping to X.400 is defined.  In most cases, the
    RFC 822 syntax is defined to make this mapping very
    straightforward, and so no detailed explanation of the mapping is
    needed.
       extended-field  = "P1-Message-ID" ":" p1-msg-id
                       / "X400-Trace" ":" x400-trace
                       / "Original-Encoded-Information-Types"
                          ":"encoded-info
                       / "P1-Content-Type" ":" p1-content-type
                       / "UA-Content-ID" ":" printablestring
                       / "Priority" ":" priority
                       / "P1-Recipient" : 1 mailbox
                       / "Deferred-Delivery" ":" date-time

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                       / "Bilateral-Info" ":" bilateral-info
                       / "Obsoletes" ":" 1 msg-id
                       / "Expiry-Date" ":" date-time
                       / "Reply-By" ":" date-time
                       / "Importance" ":" importance
                       / "Sensitivity" ":" sensitivity
                       / "Autoforwarded" ":" boolean
       p1-msg-id       = global-id ";" *text
       p1-content-type = "P2" / atom
       x400-trace      = global-id ";"
                       "arrival" date-time
                       [ "deferred" date-time ]
                       [ "action" action ]
                       [ "converted" "(" encoded-info ")" ]
                       [ "previous" global-id ]
       action          = "Relayed" / "Rerouted" / escape
       global-id       = c "*" admd [ "*" prmd ]
       encoded-info    = 1 encoded-type
       encoded-type    = "Undefined"           ; undefined (0)
                       / "Telex"               ; tLX (1)
                       / "IA5-Text"            ; iA5Text (2)
                       / "G3-Fax"              ; g3Fax (3)
                       / "TIF0"                ; tIF0 (4)
                       / "Teletex"             ; tTX (5)
                       / "Videotex"            ; videotex (6)
                       / "Voice"               ; voice (7)
                       / "SFD"                 ; sFD (8)
                       / "TIF1"                ; tIF1 (9)
                       / escape
       priority        = "normal" / "non-urgent" / "urgent" / escape
       bilateral-info  = c "*" admd "*" *text
       importance      = "low" / "normal" / "high" / escape
       sensitivity     = "Personal" / "Private"
                       / "Company-Confidential" / escape
       escape          = 1*DIGIT

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    With the exception of "Bilateral-Info:" and "X400-Trace:", there
    must be no more than one of each of these fields in an RFC 822
    header.  Any field beginning with the String "Autoforwarded-" is
    valid if the field would be syntactically valid with this string
    removed.
    The mappings to X.400 are as follows:
       P1-Message-ID:
          Mapped to P1.UMPDUEnvelope.MPDUIdentifier.  This take
          precedence over any value derived from Message-ID:.
       X400-Trace:
          Mapped to the next component of
          P1.UMPDUEnvelope.Traceinformation.  Care should be taken to
          preserve order.  If one or more of these mappings is made,
          then a trace component should NOT be generated from the
          Date: field which should be redundant.  This is because the
          message has previously come from X.400, and the Date:
          information will be redundant.  Note that all trace
          information (Received: and "X400-Trace:") in the RFC 822
          message will be in strict order, with the most recent at the
          top.  This order should be preserved in the mapping.
       Original-Encoded-Information-Types:
          This is used to set P1.UMPDUEnvelope.original.
          P1.EncodedInformationTypes.[0] has bits set according to
          each of the encoded-info components in this field.  Any
          escape values should not be encoded.
       P1-Content-Type:
          If the value is anything other than "P2", the mapping should
          not be performed (unless the new value has some semantics to
          the gateway).
       UA-Content-ID:
          Mapped to P1.UMPDUEnvelope.UAContentID.
       Priority:
          Mapped to P1.UMPDUEnvelope.Priority.  An escape value should
          be encoded as P1.Priority.normal.

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RFC 987 June 1986 Mapping between X.400 and RFC 822

       P1-Recipient:
          If this field is set, the
          P1.PerMessageFlag.discloseRecipients bit should be set.  Any
          of the addresses here which do not correspond to 822-P1
          recipients should be added to the P1 recipient list, with
          the responsibility bit turned off.
       Deferred-Delivery:
          Mapped to P1.UMPDUEnvelope.deferredDelivery.  Note that the
          value of this field should always be in the past, as this
          field should only be present in messages which have come
          originally from X.400.  Thus there should be no implied
          action.  See also the comments on the reverse mapping.
       Bilateral-Info:
          No attempt is made to reconvert this information back to
          X.400.
       Obsoletes:
          Mapped to P2.Heading.obsoletes.
       Expiry-Date:
          Mapped to P2.Heading.expiryDate.
       Reply-By:
          Mapped to P2.Heading.replyBy.
       Importance:
          Mapped to P2.Heading.importance.  An escape value should be
          encoded as P2.Heading.importance.normal.
       Sensitivity:
          Mapped to P2.Heading.sensitivity.  An escape value should be
          encoded as P2.Heading.sensitivity.normal.
       Autoforwarded:
          If this field is present and the value is "TRUE", there will
          be zero or more field names beginning "Autoforwarded-".

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          These should be taken, and the string "Autoforwarded-"
          stripped.  These fields, in conjunction with the 822-P1
          information should be used to build an IP Message.  Any
          implied actions should be taken. P2.Heading.autoforwarded is
          set in this message.  The other RFC 822 fields are used to
          build another IP Message, which is used as the single body
          part of the first message.  This mechanism does not nest.
 5.3.  Return of Contents
    It is not clear how widely supported X.400 return of contents
    service will be.  However, profiling work suggests that most
    systems will not support this service.  As this service is
    expected in the RFC 822 world, two approaches are specified (it is
    not so necessary in the X.400 world, as delivery reports are
    distinguished from messages).  The choice will depend on the
    service level of the X.400 community being serviced by the
    gateway.
    In environments where return of contents is widely supported, the
    P1.PerMessageFlag content return request bit will be set, and the
    Report Request bit in P1.PerRecipientFlag will be set to
    Confirmed, for every message passing from RFC 822 -> X.400.  The
    content return service can then be passed back to the end
    (RFC 822) user in a straightforward manner.
    In environments where return of contents is not widely supported,
    a gateway must make special provisions to handle return of
    contents.  For every message passing from RFC 822 -> X.400, the
    P1.PerMessageFlag content return request bit will be set, and the
    Report Request bit in P1.PerRecipientFlag will be set to
    Confirmed.  When the delivery report comes back, the gateway can
    note that the message has been delivered to the recipient(s) in
    question.  If a non-delivery report is received, a meaningful
    report (containing some or all of the original message) can be
    sent to the 822-P1 originator.  If no report is received for a
    recipient, a (timeout) failure notice should be sent to the 822-P1
    originator.  The gateway may retransmit the X.400 message if it
    wishes.  Delivery confirmations should only be sent back to the
    822-P1 originator if the P1.PerRecipientFlag User Report Request
    bit is set to Confirmed.

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 5.4.  X.400 -> RFC 822
    5.4.1.  General
       This section describes how to build a pro-forma message, and
       then explains how these defaults may be overridden.  It should
       be noted that RFC 822 folding of headers should be used in an
       appropriate manner.
    5.4.2.  Service MPDU
       5.4.2.1.  Probe
          Any P1.ProbeMPDU should be serviced by the gateway, as there
          is no equivalent RFC 822 functionality.  The value of the
          reply is dependent on whether the gateway could service a
          User MPDU with the values specified in the probe.  The reply
          should make use of P1.SupplementaryInformation to indicate
          that the probe was serviced by the gateway.
       5.4.2.2.  Delivery Report
          The 822-P1 components are constructed as follows:
             822-P1 Originator
                This is set to an 822.addr-spec pointing to an
                administrator at the gateway.
             822-P1 Recipient
                The single recipient is constructed from
                P1.DeliveryReportEnvelope.originator, using the
                mappings of chapter 4.
          The mandatory RFC 822 headers for an RFC 822 pro-forma are
          constructed as follows:
             Date:
                From the P1.DomainSuppliedInfo.arrival component of
                the first P1.TraceInformation component.
             From:
                This is set to the same as the 822-P1 originator.  An

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RFC 987 June 1986 Mapping between X.400 and RFC 822

                appropriate phrase component may be added (e.g. giving
                the name of the gateway).
             To:
                The same as the 822-P1 recipient.
          A Subject: field should be added, which contains some
          appropriate words (e.g. "Delivery Report").
          The other two P1.DeliveryReportEnvelope parameters should be
          mapped as follows:
             P1.DeliveryReportEnvelope.report
                This should be mapped to a P1-Message-Id: field.
             P1.DeliveryReportEnvelope.TraceInformation
                Each component should be mapped to an "X400-Trace:"
                field.  RFC 822 and X.400 ordering should be
                maintained (see 5.3).
          The P1.DeliveryReportContent parameters should be mapped to
          a series of new RFC 822 headers.  These new headers are
          intended for processing in the RFC 822 world.  No attempt
          will be made to reverse the mappings.
             drc-field    = "Delivery-Report-Content-Original"
                         ":" msg-id
               / "Delivery-Report-Content-Intermediate-Trace"
                         ":" x400-trace
               / "Delivery-Report-Content-UA-Content-ID"
                         ":" printablestring
               / "Delivery-Report-Content-Billing-Information"
                         ":" *text
               / "Delivery-Report-Content-Reported-Recipient-Info"
                         ":" drc-info
             drc-info     = mailbox ";"
                          last-trace ";"
                          "ext" 1*DIGIT
                          "flags" 2DIGIT
                          [ "intended" mailbox ] ";"
                          [ "info" printablestring ]

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             last-trace   = drc-report ";"
                          date-time ";"
                          [ "converted" "(" encoded-info ")"
             drc-report   = "SUCCESS" drc-success
                          / "FAILURE" drc-failure
             drc-success  = date-time ";" 1*DIGIT
             drc-failure  = *text [ ";" *text ] ";"
          There may be multiple
          "Delivery-Report-Content-Intermediate-Trace:" and
          "Delivery-Report-Content-Reported-Recipient-Info:" fields.
          The msg-id for "Delivery-Report-Content-Original" is derived
          according to the mapping of chapter 4.  EBNF.drc-failure may
          use numeric values or textual explanation.  The latter is
          preferred.  All P1.DeliveryReportContent parameters are
          mapped to the corresponding component.  The order of
          "Delivery-Report-Content-Intermediate-Trace:" should have
          the most recently stamped one first.
          The body of the RFC 822 message should be a human readable
          description of the critical parts of the
          P1.DeliveryReportContent.  In particular, the failed
          recipients, and failure reason should be given.  Some or all
          of the original message should be included in the delivery
          report. The original message will be available at the
          gateway, as discussed in section 5.3.
    5.4.3.  User MPDU
       These elements are the basis for both Status Report and IP
       Message.
       The 822-P1 components are constructed as follows:
          822-P1 Originator
             This is derived from P1.UMPDUEnvelope.originator.
          822-P1 Recipient
             Each recipient is constructed from the P1.RecipientInfo,
             as described in chapter 4.  This describes actions as
             well as format mappings.

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       The mandatory RFC 822 field pro-forma is derived as follows.
       In most cases where the P1.UMPDUContent is an IP Message, these
       defaults will be overridden:
          Date:
             From the P1.DomainSuppliedInfo.arrival component of the
             first P1.TraceInformation component.
          From:
             From the P1.UMPDUEnvelope.originator, as defined in
             chapter 4.
          To:
             This default is only required if the generated RFC 822
             message has no destination specification.  If
             P1.PerMessageFlag.discloseRecipients is set then it
             should contain the ORName in each P1.RecipientInfo
             component.  If it is not set, the it should be set to
             "To: No Recipients Specified : ;".
       The mappings, and any actions for each P1.UserMPDU element is
       now considered.
          P1.MPDUIdentifier
             Mapped to the extended RFC 822 field "P1-Message-ID:".
             Note that the sequence CRLF is mapped to SPACE, which
             makes the mapping irreversible for such cases.
          P1.UMPDUEnvelope.original
             Mapped to the extended RFC 822 field
             "Original-Encoded-Information-Types:".  If it contains
             only P2.IA5Text, the RFC 822 field may be omitted.
          P1.ContentType
             As this can currently only have one value, it is not
             mapped, on the basis that it is redundant.  If the field
             contains any value other than P2, then the UMPDU should
             be rejected.

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RFC 987 June 1986 Mapping between X.400 and RFC 822

          P1.UAContentID
             Mapped to the extended RFC 822 field "UA-Content-Id:".
          P1.Priority
             Mapped to the extended RFC 822 field "Priority:".
          P1.PerMesageFlag
             This has a number of components:
  1. discloseRecipients
                   If this bit is set, a "P1-Recipient:" field should
                   be generated, and contain each of the P1
                   recipients.
  1. conversionProhibited
                   If this bit is set, the message should be rejected
                   if it contains P2.BodyPart which is not P2.IA5Text
                   or P2.ForwardedIPMessage.
  1. alternateRecipientAllowed
                   The value of this bit is ignored.
  1. contentReturnRequest
                   The value of this bit is ignored.
          P1.UMPDUEnvelope.deferredDelivery
             This should be mapped to the extended RFC 822 field
             "Deferred-Delivery:".  X.400 profiles, and in particular
             the CEN/CENELEC profile [CEN/CENELEC/85a], specify that
             this element must be supported at the first MTA.  Thus,
             it is expected that the value of this element will always
             be in the past.  If it is not, the function may
             optionally be implemented by the gateway: that is, the
             gateway should hold the message until the time specified
             in the protocol element.  Thus the extended RFC 822 field
             is just for information.

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RFC 987 June 1986 Mapping between X.400 and RFC 822

          P1.PerDomainBilateralInformation
             Each component should be encoded in the extended RFC 822
             field "Bilateral-Info:".  P1.BilateralInfo should be
             mapped into ASCII in a manner appropriate to its
             contents.  This submapping is not reversible.
          P1.TraceInformation
             This should be mapped to "X400-Trace:", as for the
             delivery report.
    5.4.4.  Status Report
       The entire status report is mapped into the body of the RFC 822
       message, in the same manner as for a Delivery Report.  An
       appropriate "Subject:" field should be generated.  As status
       reports cannot be requested from the RFC 822 world, the mapping
       is not likely to be used a great deal.
    5.4.5.  IP Message
       The P1.UMPDUEnvelope pro-forma specification ensures all the
       822-P1 information, and a minimal (legal) RFC 822 message.  The
       mappings and actions for the P2.Heading components are now
       described.  Basically, these are interpreted as actions and/or
       mappings into RFC 822 fields. The following mappings are
       specified:
          P2.IPMessageID
             This is mapped to the field "Message-ID:", according to
             section 4.
          P2.Heading.originator
             If P2.Heading.authorisingUsers is present this is mapped
             to Sender:, if not to From:.
          P2.Heading.authorisingUsers
             Mapped to From:.
          P2.Heading.primaryRecipients
             Mapped to To:.

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          P2.Heading.copyRecipients
             Mapped to Cc:.
          P2.Heading.blindCopyRecipients
             Mapped to Bcc:.
          P2.Heading.inReplyTo
             Mapped to In-Reply-To:.
          P2.Heading.obsoletes
             Mapped to the extended RFC 822 field "Obsoletes:"
          P2.Heading.crossReferences
             Mapped to References:.
          P2.Heading.subject
             Mapped to subject.  The contents are converted to ASCII
             (as defined in chapter 3).  Any CRLF are not mapped, but
             are used as points at which the subject field must be
             folded.  line.
          P2.Heading.expiryDate
             Mapped to the extended RFC 822 field "Expiry-Date:".
          P2.Heading.replyBy
             Mapped to the extended RFC 822 field "Reply-By:".
          P2.Heading.replyToUsers
             Mapped to Reply-To:.
          P2.Heading.importance
             Mapped to the extended RFC 822 field "Importance:".
          P2.Heading.sensitivity
             Mapped to the extended RFC 822 field "Sensitivity:".

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          P2.Heading.autoforwarded
             If it is set to FALSE, it is simply mapped to the
             extended RFC 822 field "Autoforwarded:".  If this is set
             to TRUE, the P2.Body does not consist of a single
             P2.ForwardedIPMessage, then there is an X.400 error, and
             the message should be bounced.  Otherwise the following
             steps are taken.
                1.  The mappings for all of the message, except the
                    body part are completed.
                2.  Prepend each RFC 822 fieldname with the string
                    "Autoforwarded-". Mapped to the extended RFC 822
                    field "Autoforwarded:".
                3.  Add the field "Autoforwarded:" with value TRUE.
                4.  Convert the syntax of the P2.ForwardedIPMessage to
                    generate the remaining RFC 822 fields.
       The P2.Body is mapped into the RFC 822 message body.  Each
       P2.BodyPart is converted to ASCII.  If the P2.Body contains a
       P2.BodyPart not listed here, the entire message should be
       rejected.  If there are exactly two P2.IA5Text body parts, and
       the first line of the first is "RFC-822-Headers:", then the
       rest of this first body part should be treated as additional
       header information for the RFC 822 message.  If there is an
       "In-Reply-To:" field, this should be used to replace any
       generated In-Reply-To: field.
       In other cases of multiple P2.BodyPart, the mapping defined by
       Rose and Stefferud in [Rose85b], should be used to separate the
       P2.BodyParts in the single RFC 822 message body.
       Individual body parts are mapped as follows:
          P2.IA5Text
             The mapping is trivial.
          P2.TTX
             If any P1.Teletex.NonBasicParams are set, the message
             should be rejected.  Otherwise, it should be converted to
             ASCII according to chapter 3.

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          P2.SFD
             An SFD should be converted to ASCII as if it was being
             rendered on an 79 column ASCII only VDU.  It seems likely
             that many gateways will not support this conversion.  In
             these cases, the message should be rejected.
          P2.ForwardedIPMessage
             The P2.ForwardedIPMessage.delivery and
             P2.ForwardedIPMessage.DeliveryInformation are
             discarded <9>.  The IM-UAPDU should have its syntax
             mapped (recursively) according to this gatewaying
             specification.  Clearly, it makes no sense to apply any
             of the actions defined here.

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Appendix A – Quoted String Encodings

 This Appendix describes a quoting mechanism which may be used to
 allow general interworking between RFC 822, and variants of RFC 822
 which do not support 822.quoted-string.  This is important, as the
 basic X.400 <-> RFC 822 mapping makes use of 822.quoted-string.
 1.  ASCII <-> 822.atom
    The following EBNF is specified.
       atom-encoded    = *( a-char / a-encoded-char )
       a-char          = <any CHAR except specials, SPACE,
                               CTL, "_", and "#">
       a-encoded-char  = "_"                   ; (space)
                       / "#u#"                 ; (_)
                       / "#l#"                 ; <(>
                       / "#r#"                 ; <)>
                       / "#m#"                 ; (,)
                       / "#c#"                 ; (:)
                       / "#b#"                 ; (\)
                       / "#h#"                 ; (#)
                       / "#e#"                 ; ($=)
                       / "#s#"                 ; ($/)
                       / "#" 3DIGIT "#"
    NOTE: There are two encodings of double characters.  This is so
    that systems using this encoding, do not also need to know about
    the "$" quoting mechanism defined in chapter 4.
    The 822.3DIGIT in EBNF.a-encoded-char must have range 0-127
    (Decimal), and is interpreted in decimal as the corresponding
    ASCII character.  The choice of special abbreviations (as opposed
    to octal encoding) provided is based on the manner in which this
    mapping is most frequently used: encoding PrintableString
    components of O/R names as atom.  Therefore, there are special
    encodings for each of the PrintableString characters not in
    EBNF.a-char, except ".".  Space is given a single character
    encoding, due to its (expected) frequency of use, and backslash as
    the RFC 822 single quote character.
    To encode (ASCII -> atom): all EBNF.a-char are used directly and
    all other CHAR are encoded as EBNF.a-encoded-char.  To decode
    (822.atom -> ASCII): if 822.atom can be parsed as
    EBNF.encoded-atom reverse the previous mapping.  If it cannot be
    so parsed, map the characters directly.

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 2.  822.local-part <-> ASCII
    A related transformation is for 822.local-part (or other element
    defined as '822.word ("." 822.word)') where not 822.quoted-text is
    used.  To encode (ASCII -> 822.local-part), all EBNF.a-char and
    "." are used directly and all other 822.CHAR are encoded as
    EBNF.a-encoded-char.  To decode (822.local-part -> ASCII), first
    attempt to parse 822.local-part as '822.atom *("." 822.atom)'.  If
    this fails, or if each 822.atom cannot be parsed as
    EBNF.atom-encoded then map each character directly.  Otherwise map
    each "." directly, and each atom as in the previous section.
    There are places where it is needed to convert between
    PrintableString or IA5Text (X.400), and 822.word (RFC 822).  word
    may be encoded as 822.atom (which has a restricted character set)
    or as 822.quoted-string, which can handle all ASCII characters.
    If 822.quoted-string is used, clearly the mappings for
    PrintableString defined in Chapter 3 provide a straightforward
    mapping.  However, some RFC 822 based networks cannot handle the
    822.quoted-string format in all cases.  This Appendix is for use
    in these cases.  The major requirement for this mapping is the
    UNIX world, but it may well be needed in other places.
    These mappings are somewhat artificial, and their usage is
    discouraged, except in cases where there is no alternative.

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Appendix B – Mappings Specific to JNT Mail

 This Appendix is specific to the JNT Mail Protocol.  It describes
 specific changes in the context of this protocol.  Addressing is not
 discussed here, as it is covered in Appendix A.
 1.  Introduction
    There are four aspects of a gateway which are JNT Mail Specific,
    in addition to those relating to addressing.  These are each given
    a section of this appendix.
 2.  Acknowledge-To:
    This field has no direct functional equivalent in X.400.  However,
    it can be supported to an extent, and can be used to improve X.400
    support.
    When going from JNT Mail to X.400, the User Report Request bits of
    each P1.RecipientInfo.perRecipientFlag should be set to confirmed.
    If there is more that one address in the Acknowledge-To: field, or
    if the one address is not equivalent to the 822-P1 return address,
    then:
       a.   Acknowledgement(s) should be generated by the gateway.
            The text of these acknowledgements should indicate that
            they are generated by the gateway.
       b.   The Acknowledge-To: field should also be passed in the
            first P2.BodyPart.
    When going from X.400 to JNT Mail, in cases where
    P1.RecipientInfo.perRecipientFlag has the user bits set to
    confirmed the copy of the message to that recipient should have an
    Acknowledge-To: field containing the P.UMPDUEnvelope.originator.
    No attempt should be made to map Receipt notification requests
    onto Acknowledge-To:.  This is because no association can be
    guaranteed between P2 and P1 level addressing information.
 3.  Trace
    JNT Mail trace uses the Via: syntax.  When going from JNT Mail to
    X.400, the following mapping onto P1.TraceInformation is used.
       P1.DomainSuppliedInfo.action is set to relayed.
       P1.DomainSuppliedInfo.arrival is set to the date-time component

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       of the Via: field.  P1.DomainSuppliedInfo.previous has
       P1.CountryName as a null string, and
       P1.AdministrationDomainName as the domain specified in the Via:
       field.
       P1.TraceInformation.GlobalDomainIdentifier has P1.CountryName
       as a null string, and P1.AdministrationDomainName as any
       commented information in the Via: field.  For example:
          Via: UK.AC.Edinburgh ; 17 Jun 85 9:15:29 BST (EMAS V7)
          maps to -
          P1.GlobalDomainIdentifier
             CountryName                  = ""
             AdministrationDomainName     = "(EMAS V7)"
          P1.DomainSuppliedInfo
             arrival                      = 17 Jun 85 9:15:29 BST
             action                       = relayed
             previous
                CountryName               = ""
                AdministrationDomainName  = "UK.AC.Edinburgh"
 4.  Timezone specification
    The extended syntax of zone defined in the JNT Mail Protocol
    should be used in the mapping of UTCTime defined in chapter 3.
 5.  Lack of separate 822-P1 originator specification
    In JNT Mail the default mapping of the P1.MPDUEnvelope.originator
    is to the Sender: field.  This can cause a problem if the mapping
    of P2.Heading has already generated a Sender: field.  To overcome
    this, new extended JNT Mail field is defined.  This is chosen to
    align with the JNT recommendation for interworking with full
    RFC 822 systems [Kille84b].
       original-sender     = "Original-Sender" ":" mailbox
    If an IPM has no P2.heading.authorisingUsers component and
    P2.Heading.originator.ORName is different from
    P1.UMPDUEnvelope.originator, map P1.MPDUEnvelope.originator onto
    the Sender: field.
    If an IPM has a P2.heading.authorisingUsers component, and
    P2.Heading.originator.ORName is different from
    P1.UMPDUEnvelope.originator, P1.MPDUEnvelpoe.originator should be

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    mapped onto the Sender: field, and P2.Heading.originator mapped
    onto the Original-Sender: field.
    In other cases the P1.MPDUEnvelope.Originator is already correctly
    represented.
    Note that in some pathological cases, this mapping is
    asymmetrical.

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RFC 987 June 1986 Mapping between X.400 and RFC 822

Appendix C – Mappings Specific to Internet Mail

 The Simple Mail Transfer Protocol [Postel82a] is used in the
 ARPA-Internet, and in any network following the US DoD standards for
 internetwork protocols.  This appendix is specific to those hosts
 which use SMTP to exchange mail.
 1.   Mapping between O/R names and SMTP addresses
    The mappings of Chapter 4 are to be used.
 2.   Use of the ARPA Domain System
    Whenever possible, domain-qualified addresses should be be used to
    specify encoded O/R names.  These domain encodings naturally
    should be independent of any routing information.
 3.   Identification of gateways
    The ARPA-Internet Network Information Center (NIC) will maintain a
    list of registered X.400 gateways in the ARPA Internet.

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Appendix D – Mappings Specific to Phonenet Mail

 There are currently no mappings specific to Phonenet Mail.

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Appendix E – Mappings Specific to UUCP Mail

 Gatewaying of UUCP and X.400 is handled by first gatewaying the UUCP
 address into RFC 822 syntax (using RFC 976) [Horton86a] and then
 gatewaying the resulting RFC 822 address into X.400.  For example, an
 X.400 address
    Country         US
    Organization    Xerox
    Personal Name   John Smith
 might be expressed from UUCP as
    inthop!gate!gatehost.COM!/C=US/O=Xerox/PN=John.Smith/
 (assuming gate is a UUCP-ARPA gateway and gatehost.COM is an
 ARPA-X.400 gateway) or
    inthop!gate!Xerox.COM!John.Smith
 (assuming that Xerox.COM and /C=US/O=Xerox/ are equivalent.)
 In the other direction, a UUCP address Smith@ATT.COM, integrated into
 822, would be handled as any other 822 address.  A non-integrated
 address such as inthop!dest!user might be handled thought a pair of
 gateways:
    Country         US
    ADMD            ATT
    PRMD            ARPA
    Organization    GateOrg
    RFC-822         inthop!dest!user@gatehost.COM
 or through a single X.400 to UUCP gateway:
    Country         US
    ADMD            ATT
    PRMD            UUCP
    Organization    GateOrg
    UUCP            inthop!dest!user

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Appendix F – Format of Address Mapping Tables

 There is a need to specify the association between the domain and
 X.400 namespaces described in 4.2.1.  This is defined as a table
 syntax, but the syntax is defined in a manner which makes it suitable
 for use with domain nameservers (such as the DARPA Domain nameservers
 or the UK NRS).  The symmetry of the mapping is not clear, so a
 separate table is specified for each direction.  For domain -> X.400:
    domain-syntax "#" dmn-orname "#"
    For example:
    AC.UK#PRMD$DES.ADMD$BT.C$UK#
    XEROX.COM#O$Xerox.ADMD$ATT.C$US#
 For X.400 -> domain:
    dmn-orname "#" domain-syntax "#"
 EBNF.domain-syntax will be interpreted according to RFC 920.
 EBNF.dmn-orname will have components ordered as defined in section
 4.2.1, and with the most significant component on the RHS.

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References

 Bonacker85a.
    K.H. Bonacker, U. Pankoke-Babatz, and H. Santo, "EAN - Conformity
    to X.400 and DFN-Pflichtenheft," GMD (Gesellschaft fur Mathematik
    und Datenverarbeitung) report, June 1985.
 CCITT84a.
    CCITT SG 5/VII, "Recommendations X.400," Message Handling Systems:
    System Model - Service Elements, October 1984.
 CCITT84b.
    CCITT SG 5/VII, "Recommendations X.411," Message Handling Systems:
    Message Transfer Layer, October 1984.
 CCITT84c.
    CCITT SG 5/VII, "Recommendations X.420," Message Handling Systems:
    Interpersonal Messaging User Agent Layer, October 1984.
 CCITT84d.
    CCITT SG 5/VII, "Recommendations X.409," Message Handling Systems:
    Presentation Transfer Syntax and Notation, October 1984.
 CEN/CENELEC/85a.
    CEN/CENELEC/Information Technology/Working Group on Private
    Message Handling Systems, "FUNCTIONAL STANDARD A/3222,"
    CEN/CLC/IT/WG/PMHS N 17, October 1985.
 Crocker82a.
    D.H. Crocker, "Standard of the Format of ARPA Internet Text
    Messages," RFC 822, August 1982.
 Horton85a.
    M.R. Horton, "Draft Standard for ARPA/MHS Addressing Gateways,"
    AT&T Bell Laboratories, October 1985.

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 Horton86a.
    M.R. Horton, "UUCP Mail Interchange Format Standard", RFC 976,
    February 1986.
 ICL84a.
    ICL, "Comparison of service elements of Grey Book Mail and X.400,"
    Mailgroup Note 18: Extract from unpublished report for ITSU
    (Information Technology Standards Unit), July 1984.
 Kille84a.
    S.E. Kille, (editor), JNT Mail Protocol (revision 1.0), Joint
    Network Team, Rutherford Appleton Laboratory, March 1984.
 Kille84b.
    S.E. Kille, "Gatewaying between RFC 822 and JNT Mail," JNT
    Mailgroup Note 15, May 1984.
 Kille86a.
    S.E. Kille, "O/R Names in the UK Academic Community," UK Working
    Document, March 1986.
 Larmouth83a.
    J. Larmouth, "JNT Name Registration Technical Guide," Salford
    University Computer Centre, April 1983.
 Neufeld85a.
    G. Neufeld, J. Demco, B. Hilpert, and R. Sample, "EAN: an X.400
    message system," in Second International Symposium on Computer
    Message Systems, Washington, pp. 1-13, North Holland,
    September 1985.
 Postel82a.
    J. Postel, "Simple Mail Transfer Protocol," RFC 821, August 1982.
 Postel84a.
    J. Postel and J. Reynolds, "Domain Requirements," RFC 920,
    October 1984.

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 Rose85a.
    M.T. Rose, "Mapping Service Elements between ARPA and MHS," Draft
    proposal, October 1985.
 Rose85b.
    M.T. Rose and E.A. Stefferud, "Proposed Standard for Message
    Encapsulation," RFC 934, January 1985.

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Notes:

 <0>  UNIX is a trademark of Bell Laboratories.
 <1>  The term gateway is used to describe a component performing the
      protocol mappings between RFC 822 and X.400.  This is standard
      usage amongst mail implementors, but should be noted carefully
      by transport and network service implementors.  (Sometime called
      a "mail relay".)
 <2>  If the remote protocol is JNT Mail, a notification may also be
      sent by the recipient UA.
 <3>  The asymmetry occurs where an ASCII string contains the sequence
      EBNF.ps-encoded-char.  This would be mapped directly to
      PrintableString, but the reverse mapping would be to the value
      implied by the sequence.
 <4>  It might be suggested that for reasons of elegance,
      EBNF.ps-delim (left parenthesis) is encoded as
      EBNF.ps-encoded-char. This is not done, as it it would never be
      possible to represent a PrintableString containing the character
      "(" in ASCII.  This is because an "(" in ASCII would be mapped
      to the encoding in PrintableString.
 <5>  In practice, a gateway will need to parse various illegal
      variants on 822.date-time.  In cases where 822.date-time cannot
      be parsed, it is recommended that the derived UTCTime is set to
      the value at the time of translation.
 <6>  P2.ORname is defined as P1.ORName.
 <7>  This recommendation may change in the light of CCITT or
      CEN/CENELEC guidelines on the use of initials.
 <8>  It would be possible to use a ForwardedIPMessage for these
      fields, but the semantics are (arguably) slightly different, and
      it is probably not worth the effort.
 <9>  Although this violates chapter 1, part 4, principles 2 and 3, it
      is suggested that this is justified by principle 1.

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