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RFC 0987

Mapping between X.400 and RFC 822

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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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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].


            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.


            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

   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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              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

         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.


               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

         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

      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:

         -    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].

         -    An unpublished ICL report, which considered a subset of
              the problem [ICL84a].

         -    A document by Marshall Rose [Rose85a].
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         -    A document by Mark Horton [Horton85a].  The string
              encodings of chapter 3 were derived directly from this
              work, as is much of chapter 4.

         -    Discussion on a number of electronic mailing lists.

         -    Meetings in the UK and the US.
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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:

      -    Semantic correspondence.

      -    No loss of information.

      -    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

   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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            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:.














            Supported, for a single reference in msg-id form.  Other
            cases are passed in the message text.




            Passed in the message text.
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            Passed in the message text.


            Passed in the message text.  This may not be very useful.


            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

   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

      2.2.1.  Message Transfer Service Elements

         Access Management

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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


         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


         Submission Time Stamp Indication


         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


         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


         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.


            Supported at the gateway (i.e. the gateway services the

         Alternate Recipient Assignment


         Hold for Delivery


      2.2.2.  Interpersonal Message Service Elements

         IP-message Identification


         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


         Non-receipt Notification

            Not supported.

         Receipt Notification

            Not supported.
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         Auto-forwarded Indication

            Supported as new RFC 822 header.

         Originator Indication


         Authorising User's Indication

            Supported, although the mapping (From:) is not quite the

         Primary and Copy Recipients Indication


         Expiry Date Indication

            Supported as new RFC 822 header.  In general, only human
            action can be expected.

         Cross Referencing Indication


         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


         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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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

         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.

            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

      3.1.5.  X.409

         An element is referred to with the following syntax, defined in

            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 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 syntax is used, with all AND mapped directly <4>.  All other 822.CHAR are
         encoded as There are two cases of
         encoding PrintableString as ASCII.  If the PrintableString can
         be parsed as, then the previous mapping should
         be reversed.  If not, it should be interpreted as

         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 syntax contain: Year
         (lowest two digits), Month, Day of Month, hour, minute, second
         (optional), and Timezone. 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

         attributevalue = c / admd / prmd / x121 / t-id / o / ou
                         / ua-id / pn.g / pn.i / pn.s / / 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    = printablestring       ; P1.PersonalName.generation
         dd.value = printablestring       ; P1.DomainDefined

         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.
ToP   noToC   RFC0987 - Page 23
         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.
ToP   noToC   RFC0987 - Page 24
         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.
ToP   noToC   RFC0987 - Page 25
            std-orname      = 1*( "/" attribute "=" value ) "/"
            attribute       = standard-type
                            / "PN"
                            / standard-dd-type
                            / registered-dd-type
                            / "DD." std-printablestring
            value           = std-printablestring
                            = 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  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
ToP   noToC   RFC0987 - Page 26
   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

         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

         A generic 822.address consists of a 822.local-part and a
         sequence of (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
ToP   noToC   RFC0987 - Page 27
         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

            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
ToP   noToC   RFC0987 - Page 28
         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:


            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
ToP   noToC   RFC0987 - Page 29
      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

         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

            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

         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:


            C               = "GB"
            ADMD            = "BT"
            PRMD            = "AC"
            "JNT-Mail"      = "Jimmy(a)UK.CO.BT-RESEARCH-LABS"


            C               = "US"
            ADMD            = "Telemail"
            PRMD            = "San Fransisco"
            O               = "U Cal"
            OU              = "Berkeley"
            "RFC-822"       = "postel(a)"
ToP   noToC   RFC0987 - Page 30
         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

            2.   "Genuine" RFC 822 addresses.

         The mapping should proceed as follows, by first assuming case

         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).
ToP   noToC   RFC0987 - Page 31
               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 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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