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RFC 1327


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Mapping between X.400(1988) / ISO 10021 and RFC 822

Part 1 of 4, p. 1 to 24
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Obsoleted by:    2156
Obsoletes:    0987    1026    1138    1148
Updates:    0822
Updated by:    1495


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Network Working Group                                S. Hardcastle-Kille
Request for Comments: 1327                     University College London
Obsoletes: RFCs 987, 1026, 1138, 1148                           May 1992
Updates: RFC 822


          Mapping between X.400(1988) / ISO 10021 and RFC 822

Status of this Memo

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

Abstract

   This document describes a set of mappings which will enable
   interworking between systems operating the CCITT X.400 1988)
   Recommendations on Message Handling Systems / ISO IEC 10021 Message
   Oriented Text Interchange Systems (MOTIS) [CCITT/ISO88a], 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
   document is a revision based on RFCs 987, 1026, 1138, and 1148
   [Kille86a,Kille87a] which it obsoletes.

   This document specifies a mapping between two protocols.  This
   specification should be used when this mapping is performed on the
   DARPA Internet or in the UK Academic Community.  This specification
   may be modified in the light of implementation experience, but no
   substantial changes are expected.

Table of Contents

   1          - Overview ......................................    3
   1.1        - X.400 .........................................    3
   1.2        - RFC 822 .......................................    3
   1.3        - The need for conversion .......................    4
   1.4        - General approach ..............................    4
   1.5        - Gatewaying Model ..............................    5
   1.6        - X.400 (1984) ..................................    8
   1.7        - Compatibility with previous versions ..........    8
   1.8        - Aspects not covered ...........................    8
   1.9        - Subsetting ....................................    9
   1.10       - Document Structure ............................    9

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   1.11       - Acknowledgements ..............................    9
   2          - Service Elements ..............................   10
   2.1        - The Notion of Service Across a Gateway ........   10
   2.2        - RFC 822 .......................................   11
   2.3        - X.400 .........................................   15
   3          - Basic Mappings ................................   24
   3.1        - Notation ......................................   24
   3.2        - ASCII and IA5 .................................   26
   3.3        - Standard Types ................................   26
   3.4        - Encoding ASCII in Printable String ............   28
   4          - Addressing ....................................   30
   4.1        - A textual representation of MTS.ORAddress .....   30
   4.2        - Basic Representation ..........................   31
   4.3        - EBNF.822-address <-> MTS.ORAddress ............   36
   4.4        - Repeated Mappings .............................   48
   4.5        - Directory Names ...............................   50
   4.6        - MTS Mappings ..................................   50
   4.7        - IPMS Mappings .................................   55
   5          - Detailed Mappings .............................   59
   5.1        - RFC 822 -> X.400 ..............................   59
   5.2        - Return of Contents ............................   67
   5.3        - X.400 -> RFC 822 ..............................   67
   Appendix A - Mappings Specific to SMTP .....................   91
   Appendix B - Mappings specific to the JNT Mail .............   91
   1          - Introduction ..................................   91
   2          - Domain Ordering ...............................   91
   3          - Addressing ....................................   91
   4          - Acknowledge-To:  ..............................   91
   5          - Trace .........................................   92
   6          - Timezone specification ........................   92
   7          - Lack of 822-MTS originator specification ......   92
   Appendix C - Mappings specific to UUCP Mail ................   93
   Appendix D - Object Identifier Assignment ..................   94
   Appendix E - BNF Summary ...................................   94
   Appendix F - Format of address mapping tables ..............  101
   1          - Global Mapping Information ....................  101
   2          - Syntax Definitions ............................  102
   3          - Table Lookups .................................  103
   4          - Domain -> O/R Address format ..................  104
   5          - O/R Address -> Domain format ..................  104
   6          - Domain -> O/R Address of Gateway table ........  104
   Appendix G - Mapping with X.400(1984) ......................  105
   Appendix H - RFC 822 Extensions for X.400 access ...........  106
   Appendix I - Conformance ...................................  106
   Appendix J - Change History: RFC 987, 1026, 1138, 1148 .....  107
   1          - Introduction ..................................  108
   2          - Service Elements ..............................  108
   3          - Basic Mappings ................................  108

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   4          - Addressing ....................................  108
   5          - Detailed Mappings .............................  109
   6          - Appendices ....................................  109
   Appendix K - Change History: RFC 1148 to this Document .....  109
   1          - General .......................................  109
   2          - Basic Mappings ................................  110
   3          - Addressing ....................................  110
   4          - Detailed Mappings .............................  110
   5          - Appendices ....................................  110
   References .................................................  111
   Security Considerations ....................................  113
   Author's Address ...........................................  113

Chapter 1 -- Overview

1.1.  X.400

   This document relates to the CCITT 1988 X.400 Series Recommendations
   / ISO IEC 10021 on the Message Oriented Text Interchange Service
   (MOTIS).  This ISO/CCITT standard is referred to in this document as
   "X.400", which is a convenient shorthand.  Any reference to the 1984
   CCITT Recommendations will be explicit.  X.400 defines an
   Interpersonal Messaging System (IPMS), making use of a store and
   forward Message Transfer System.  This document relates to the IPMS,
   and not to wider application of X.400.  It is expected that X.400
   will be implemented very widely.

1.2. RFC 822

   RFC 822 evolved as a messaging standard on the DARPA (the US Defense
   Advanced Research Projects Agency) Internet.  It specifies and end to
   end message format.  It is used in conjunction with a number of
   different message transfer protocol environments.

   SMTP Networks
       On the DARPA Internet and other TCP/IP networks, RFC 822 is
       used 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 domains and a
       distributed name service [Postel84a].

   UUCP Networks
       UUCP is the UNIX to UNIX CoPy protocol, 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 use domains
       which conform to RFC 920, but not the corresponding domain
       nameservers [Horton86a].

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   Bitnet
       Some parts of Bitnet and related networks use RFC 822
       related protocols, with EBCDIC encoding.

   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 users of the IPMS
   provided by X.400 systems.  This will also be a requirement in cases
   where communities intend to make a transition to use of an X.400
   IPMS, as conversion will be needed to ensure a smooth service
   transition.  It is expected that there will be more than one gateway,
   and this specification will enable them to behave in a consistent
   manner.  Note that 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.

   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.  These principles are goals, and are not achieved in
   all aspects 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.

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   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
        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.

   5.   Subject to 1), the specification should be reversible.  That
        is, a double transformation should bring you back to where
        you started.

1.5.  Gatewaying Model

1.5.1.  X.400

   X.400 defines the IPMS Abstract Service in X.420/ISO 10021-7,
   [CCITT/ISO88b] which comprises of three basic services:

   1.   Origination

   2.   Reception

   3.   Management

   Management is a local interaction between the user and the IPMS, and
   is therefore not relevant to gatewaying.  The first two services
   consist of operations to originate and receive the following two
   objects:

   1.   IPM (Interpersonal Message). 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 heading consists of
        fields containing end to end user information, such as
        subject, primary recipients (To:), and importance.

   2.   IPN (Inter Personal Notification).  A notification  about
        receipt of a given IPM at the UA level.

   The Origination service also allows for origination of a probe, which
   is an object to test whether a given IPM could be correctly received.

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   The Reception service also allows for receipt of Delivery Reports
   DR), which indicate delivery success or failure.

   These IPMS Services utilise the Message Transfer (MT) Abstract
   Service [CCITT/ISO88c].  The MT Abstract Service provides the
   following three basic services:

   1.   Submission (used by IPMS Origination)

   2.   Delivery (used by IPMS Reception)

   3.   Administration (used by IPMS Management)

   Administration is a local issue, and so does not affect this
   standard.  Submission and delivery relate primarily to the MTS
   Message (comprising Envelope and Content), which carries an IPM or
   IPN (or other uninterpreted contents).  There is also an Envelope,
   which includes an ID, an originator, and a list of recipients.
   Submission also includes the probe service, which supports the IPMS
   Probe. Delivery also includes Reports, which indicate whether a given
   MTS Message has been delivered or not.

   The MTS is REFINED into the MTA (Message Transfer Agent) Service,
   which defines the interaction between MTAs, along with the procedures
   for distributed operation.  This service provides for transfer of MTS
   Messages, Probes, and Reports.

1.5.2.  RFC 822

   RFC 822 is based on the assumption that there is an underlying
   service, which is here called the 822-MTS service.  The 822-MTS
   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.

   It is possible to achieve 2) within the RFC 822 header.  Some 822-MTS
   protocols, in particular SMTP, can provide additional functionality,
   but as these are neither mandatory in SMTP, nor available in other
   822-MTS protocols, they are not considered here.  Details of aspects
   specific to two 822-MTS protocols are given in Appendices B and C.
   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
   heading fields, although some are analogous to MTS Service Elements

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   or MTA Service Elements.

1.5.3.  The Gateway

   Given this functional description of the two services, the functional
   nature of a gateway can now be considered.  It would be elegant to
   consider the 822-MTS service mapping onto the MTS Service Elements
   and RFC 822 mapping onto an IPM, but reality just does not fit.
   Another elegant approach would be to treat this document as the
   definition of an X.400 Access Unit (AU).  Again, reality does not
   fit.  It is necessary to consider that the IPM format definition, the
   IPMS Service Elements, the MTS Service Elements, and MTA Service
   Elements on one side are mapped into RFC 822 + 822-MTS on the other
   in a slightly tangled manner.  The details of the tangle will be made
   clear in Chapter 5.  Access to the MTA Service Elements is minimised.

   The following basic mappings are thus defined.  When going from RFC
   822 to X.400, an RFC 822 message and the associated 822-MTS
   information is always mapped into an IPM (MTA, MTS, and IPMS
   Services).  Going from X.400 to RFC 822, an RFC 822 message and the
   associated 822-MTS information may be derived from:

   1.   A Report (MTA, and MTS Services)

   2.   An IPN (MTA, MTS, and IPMS services)

   3.   An IPM (MTA, MTS, and IPMS services)

   Probes (MTA Service) must be processed by the gateway, as discussed
   in Chapter 5.  MTS Messages containing Content Types other than those
   defined by the IPMS are not mapped by the gateway, and should be
   rejected at the gateway.

1.5.4.  Repeated Mappings

   The primary goal of this specification is to support single mappings,
   so that X.400 and RFC 822 users can communicate with maximum
   functionality.

   The mappings specified here are designed to work where a message
   traverses multiple times between X.400 and RFC 822. This is often
   essential, particularly in the case of distribution lists.  However,
   in general, this will lead to a level of service which is the lowest
   common denominator (approximately the services offered by RFC 822).

   Some RFC 822 networks may wish to use X.400 as an interconnection
   mechanism (typically for policy reasons), and this is fully
   supported.

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   Where an X.400 messages transfers to RFC 822 and then back to X.400,
   there is no expectation of X.400 services which do not have an
   equivalent service in standard RFC 822 being preserved - although
   this may be possible in some cases.

1.6.  X.400 (1984)

   Much of this work is based on the initial specification of RFC 987
   and in its addendum RFC 1026, which defined a mapping between
   X.400(1984) and RFC 822.  A basic decision is that the mapping
   defined in this document is to the full 1988 version of X.400, and
   not to a 1984 compatible subset. New features of X.400(1988) can be
   used to provide a much cleaner mapping than that defined in RFC 987.
   This is important, to give good support to communities which will
   utilise full X.400 at an early date.   To interwork with 1984
   systems, Appendix G shall be followed.

   If a message is being transferred to an X.400(1984) system by way of
   X.400(1988) MTA it will give a slightly better service to follow the
   rules of Appendix G.

1.7.  Compatibility with previous versions

   The changes between this and older versions of the document are given
   in Appendices I and J.    These are RFCs 987, 1026, 1138, and 1148.
   This document is a revision of RFC 1148 [Kille90a].  As far as
   possible, changes have been made in a compatible fashion.

1.8.  Aspects not covered

   There have been a number of cases where RFC 987 was used in a manner
   which was not intended.  This section is to make clear some
   limitations of scope.  In particular, this specification does not
   specify:

   -   Extensions of RFC 822 to provide access to all X.400
       services

   -    X.400 user interface definition

   -    Mapping X.400 to extended versions of RFC 822, with support
        for multimedia content.

   The first two of these are really coupled.  To map the X.400
   services, this specification defines a number of extensions to RFC
   822.  As a side effect, these give the 822 user access to SOME X.400
   services.  However, the aim on the RFC 822 side is to preserve
   current service, and it is intentional that access is not given to

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   all X.400 services.  Thus, it will be a poor choice for X.400
   implementors to use RFC 987(88) as an interface - there are too many
   aspects of X.400 which cannot be accessed through it.  If a text
   interface is desired, a specification targeted at X.400, without RFC
   822 restrictions, would be more appropriate.  Some optional and
   limited extensions in this area have proved useful, and are defined
   in Appendix H.

1.9.  Subsetting

   This proposal specifies a mapping which is appropriate to preserve
   services in existing RFC 822 communities.  Implementations and
   specifications which subset this specification are strongly
   discouraged.

1.10.  Document Structure

   This document has five chapters:

   1.   Overview - this chapter.

   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.   Detailed Mappings - This describes the details of all other
        mappings.

   There are also eleven appendices.

   WARNING:
        THE REMAINDER OF THIS SPECIFICATION IS TECHNICALLY DETAILED.
        IT WILL NOT MAKE SENSE, EXCEPT IN THE CONTEXT OF RFC 822 AND
        X.400 (1988).  DO NOT ATTEMPT TO READ THIS DOCUMENT UNLESS
        YOU ARE FAMILIAR WITH THESE SPECIFICATIONS.

1.11.  Acknowledgements

   The work in this specification was substantially based on RFC 987 and
   RFC 1148, which had input from many people, who are credited in the
   respective documents.

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   A number of comments from people on RFC 1148 lead to this document.
   In particular, there were comments and suggestions from:  Maurice
   Abraham (HP); Harald Alvestrand (Sintef); Peter Cowen (X-Tel); Jim
   Craigie (JNT); Ella Gardener (MITRE); Christian Huitema (Inria); Erik
   Huizer (SURFnet); Neil Jones DEC); Ignacio Martinez (IRIS); Julian
   Onions (X-Tel); Simon Poole (SWITCH); Clive Roberts (Data General);
   Pete Vanderbilt SUN); Alan Young (Concurrent).

Chapter 2 - Service Elements

   This chapter considers the services offered across a gateway built
   according to this specification.  It gives a view of the
   functionality provided by such a gateway for communication with users
   in the opposite domain.  This chapter considers service mappings in
   the context of SINGLE transfers only, and not repeated mappings
   through multiple gateways.

2.1.  The Notion of Service Across a Gateway

   RFC 822 and X.400 provide a number of services to the end user.  This
   chapter 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.

2.1.1.  Origination of Messages

   When a user originates a message, a number of services are available.
   Some of these imply actions (e.g., delivery to a recipient), and some
   are insertion of known data (e.g., specification of a subject field).
   This chapter describes, for each offered service, to what extent it
   is supported for a recipient accessed through a gateway.  There are
   three levels of support:

   Supported
        The corresponding protocol elements map well, and so the
        service can be fully provided.

   Not Supported
        The service cannot be provided, as there is a complete
        mismatch.

   Partial Support
        The service can be partially fulfilled.

   In the first two cases, the service is simply marked as Supported" or
   "Not Supported".  Some explanation may be given if there are
   additional implications, or the (non) support is not intuitive.  For

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   partial support, the level of partial support is summarised.  Where
   partial support is good,  this will be described by a phrase such as
   "Supported by use of.....".  A common case of this is where the
   service is mapped onto a non- standard service on the other side of
   the gateway, and this would have lead to support if it had been a
   standard service.  In many cases, this is equivalent to support.  For
   partial support, an indication of the mechanism is given, in order to
   give a feel for the level of support provided.  Note that this is not
   a replacement for Chapter 5, where the mapping is fully specified.

   If a service is described as supported, this implies:

   -    Semantic correspondence.

   -    No (significant) loss of information.

   -    Any actions required by the service element.

   An example of a service gaining full support: 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.

   In many cases, the required action will simply be to make the
   information available to the end user.  In other cases, actions may
   imply generating a delivery report.

   All RFC 822 services are supported or partially supported for
   origination.  The implications of non-supported X.400 services is
   described under X.400.

2.1.2.  Reception of Messages

   For reception, the list of service elements required to support this
   mapping is specified.  This is really an indication of what a
   recipient might expect to see in a message which has been remotely
   originated.

2.2.  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.

2.2.1.  Origination in RFC 822

   A mechanism of mapping, used in several cases, is to map the RFC 822
   header into a heading extension in the IPM (InterPersonal Message).

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   This can be regarded as partial support, as it makes the information
   available to any X.400 implementations which are interested in these
   services. Communities which require significant RFC 822 interworking
   are recommended to require that their X.400 User Agents are able to
   display these heading extensions.  Support for the various service
   elements (headers) is now listed.

   Date:
        Supported.

   From:
        Supported.  For messages where there is also a sender field,
        the mapping is to "Authorising Users Indication", 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.  Where multiple
        references are given, partial support is given by mapping to
        "Cross Referencing Indication".  This gives similar
        semantics.

   References:
        Supported.

   Keywords:
        Supported by use of a heading extension.

   Subject:
        Supported.

   Comments:
        Supported by use of an extra body part.

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   Encrypted:
        Supported by use of a heading extension.

   Resent-*
        Supported by use of a heading extension.  Note that
        addresses in these fields are mapped onto text, and so are
        not accessible to the X.400 user as addresses.  In
        principle, fuller support would be possible by mapping onto
        a forwarded IP Message, but this is not suggested.

   Other Fields
        In particular X-* fields, and "illegal" fields in common
        usage (e.g., "Fruit-of-the-day:") are supported by use of
        heading extensions.

2.2.2.  Reception by RFC 822

   This considers reception by an RFC 822 User Agent of a message
   originated in an X.400 system and transferred across a gateway.  The
   following standard services (headers) may be present in such a
   message:

   Date:

   From:

   Sender:

   Reply-To:

   To:

   Cc:

   Bcc:

   Message-Id:

   In-Reply-To:

   References:

   Subject:

   The following non-standard services (headers) may be present.  These
   are defined in more detail in Chapter 5 (5.3.4, 5.3.6, 5.3.7):

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   Autoforwarded:

   Content-Identifier:

   Conversion:

   Conversion-With-Loss:

   Delivery-Date:

   Discarded-X400-IPMS-Extensions:

   Discarded-X400-MTS-Extensions:

   DL-Expansion-History:

   Deferred-Delivery:

   Expiry-Date:

   Importance:

   Incomplete-Copy:

   Language:

   Latest-Delivery-Time:

   Message-Type:

   Obsoletes:

   Original-Encoded-Information-Types:

   Originator-Return-Address:

   Priority:

   Reply-By:

   Requested-Delivery-Method:

   Sensitivity:

   X400-Content-Type:

   X400-MTS-Identifier:

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   X400-Originator:

   X400-Received:

   X400-Recipients:

2.3.  X.400

2.3.1.  Origination in X.400

   When mapping services from X.400 to RFC 822 which are not supported
   by RFC 822, 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 partially
   supported.  Chapter 5 describes how to map X.400 services onto these
   new headers.  Other elements are provided, in part, by the gateway as
   they cannot be provided by RFC 822.

   Some service elements are marked N/A (not applicable).  There are
   five cases, which are marked with different comments:

   N/A (local)
        These elements are only applicable to User Agent / Message
        Transfer Agent interaction and so they cannot apply to RFC
        822 recipients.

   N/A (PDAU)
        These service elements are only applicable where the
        recipient is reached by use of a Physical Delivery Access
        Unit (PDAU), and so do not need to be mapped by the gateway.

   N/A (reception)
        These services  are only applicable for reception.

   N/A (prior)
        If requested, this service must be performed prior to the
        gateway.

   N/A (MS)
        These services are only applicable to Message Store (i.e., a
        local service).

   Finally, some service elements are not supported.  In particular, the
   new security services are not mapped onto RFC 822.  Unless otherwise
   indicated, the behaviour of service elements marked as not supported
   will depend on the criticality marking supplied by the user.  If the
   element is marked as critical for transfer or delivery, a non-

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   delivery notification will be generated.  Otherwise, the service
   request will be ignored.

2.3.1.1.  Basic Interpersonal Messaging Service

   These are the mandatory IPM services as listed in Section 19.8 of
   X.400 / ISO/IEC 10021-1, listed here in the order given. Section 19.8
   has cross references to short definitions of each service.

   Access management
        N/A (local).

   Content Type Indication
        Supported by a new RFC 822 header (Content-Type:).

   Converted Indication
        Supported by a new RFC 822 header (X400-Received:).

   Delivery Time Stamp Indication
        N/A (reception).

   IP Message Identification
        Supported.

   Message Identification
        Supported, by use of a new RFC 822 header
        (X400-MTS-Identifier).  This new header is required, as
        X.400 has two message-ids whereas RFC 822 has only one (see
        previous service).

   Non-delivery Notification
        Not supported, although in general an RFC 822 system will
        return error reports by use of IP messages.  In other
        service elements, this pragmatic result can be treated as
        effective support of this service element.

   Original Encoded Information Types Indication
        Supported as a new RFC 822 header
        (Original-Encoded-Information-Types:).

   Submission Time Stamp Indication
        Supported.

   Typed Body
        Some types supported.  IA5 is fully supported.
        ForwardedIPMessage is supported, with some loss of
        information.  Other types get some measure of support,
        dependent on X.400 facilities for conversion to IA5.  This

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        will only be done where content conversion is not
        prohibited.

   User Capabilities Registration
        N/A (local).

2.3.1.2.  IPM Service Optional User Facilities

   This section describes support for the optional (user selectable) IPM
   services as listed in Section 19.9 of X.400 / ISO/IEC 10021- 1,
   listed here in the order given.  Section 19.9 has cross references to
   short definitions of each service.

   Additional Physical Rendition
        N/A (PDAU).

   Alternate Recipient Allowed
        Not supported.  There is no RFC 822 service equivalent to
        prohibition of alternate recipient assignment (e.g., an RFC
        822 system may freely send an undeliverable message to a
        local postmaster).  Thus, the gateway cannot prevent
        assignment of alternative recipients on the RFC 822 side.
        This service really means giving the user control as to
        whether or not an alternate recipient is allowed. This
        specification requires transfer of messages to RFC 822
        irrespective of this service request, and so this service is
        not supported.

   Authorising User's Indication
        Supported.

   Auto-forwarded Indication
        Supported as new RFC 822 header (Auto-Forwarded:).

   Basic Physical Rendition
        N/A (PDAU).

   Blind Copy Recipient Indication
        Supported.

   Body Part Encryption Indication
        Supported by use of a new RFC 822 header
        (Original-Encoded-Information-Types:), although in most
        cases it will not be possible to map the body part in
        question.

   Content Confidentiality
        Not supported.

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   Content Integrity
        Not supported.

   Conversion Prohibition
        Supported.  In this case, only messages with IA5 body parts,
        other body parts which contain only IA5, and Forwarded IP
        Messages (subject recursively to the same restrictions),
        will be mapped.

   Conversion Prohibition in Case of Loss of Information
        Supported.

   Counter Collection
        N/A (PDAU).

   Counter Collection with Advice
        N/A (PDAU).

   Cross Referencing Indication
        Supported.

   Deferred Delivery
        N/A (prior).  This service should always be provided by the
        MTS prior to the gateway.  A new RFC 822 header
        Deferred-Delivery:) is provided to transfer information on
        this service to the recipient.

Deferred Delivery Cancellation
      N/A (local).

Delivery Notification
      Supported.  This is performed at the gateway.  Thus, a
      notification is sent by the gateway to the originator.  If
      the 822-MTS protocol is JNT Mail, a notification may also be
      sent by the recipient UA.

Delivery via Bureaufax Service
      N/A (PDAU).

Designation of Recipient by Directory Name
      N/A (local).

Disclosure of Other Recipients
      Supported by use of a new RFC 822 header (X400-Recipients:).
      This is descriptive information for the RFC 822 recipient,
      and is not reverse mappable.

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DL Expansion History Indication
      Supported by use of a new RFC 822 header
      DL-Expansion-History:).

DL Expansion Prohibited
      Distribution List means MTS supported distribution list, in
      the manner of X.400.  This service does not exist in the RFC
      822 world.  RFC 822 distribution lists should be regarded as
      an informal redistribution mechanism, beyond the scope of
      this control.  Messages will be sent to RFC 822,
      irrespective of whether this service is requested.
      Theoretically therefore, this service is supported, although
      in practice it may appear that it is not supported.

Express Mail Service
      N/A (PDAU).

Expiry Date Indication
      Supported as new RFC 822 header (Expiry-Date:).  In general,
      no automatic action can be expected.

Explicit Conversion
      N/A (prior).

Forwarded IP Message Indication
      Supported, with some loss of information.  The message is
      forwarded in an RFC 822 body, and so can only be interpreted
      visually.

Grade of Delivery Selection
      N/A (PDAU)

Importance Indication
      Supported as new RFC 822 header (Importance:).

Incomplete Copy Indication
      Supported as new RFC 822 header (Incomplete-Copy:).

Language Indication
      Supported as new RFC 822 header (Language:).

Latest Delivery Designation
      Not supported.  A new RFC 822 header (Latest-Delivery-Time:)
      is provided, which may be used by the recipient.

Message Flow Confidentiality
      Not supported.

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Message Origin Authentication
      N/A (reception).

Message Security Labelling
      Not supported.

Message Sequence Integrity
      Not supported.

Multi-Destination Delivery
      Supported.

Multi-part Body
      Supported, with some loss of information, in that the
      structuring cannot be formalised in RFC 822.

Non Receipt Notification Request
      Not supported.

Non Repudiation of Delivery
      Not supported.

Non Repudiation of Origin
      N/A (reception).

Non Repudiation of Submission
      N/A (local).

Obsoleting Indication
      Supported as new RFC 822 header (Obsoletes:).

Ordinary Mail
      N/A (PDAU).

Originator Indication
      Supported.

Originator Requested Alternate Recipient
      Not supported, but is placed as comment next to address
      X400-Recipients:).

Physical Delivery Notification by MHS
      N/A (PDAU).

Physical Delivery Notification by PDS
      N/A (PDAU).

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Physical Forwarding Allowed
      Supported by use of a comment in a new RFC 822 header
      X400-Recipients:), associated with the recipient in
      question.

Physical Forwarding Prohibited
      Supported by use of a comment in a new RFC 822 header
      X400-Recipients:), associated with the recipient in
      question.

Prevention of Non-delivery notification
      Supported, as delivery notifications cannot be generated by
      RFC 822.  In practice, errors will be returned as IP
      Messages, and so this service may appear not to be supported
      see Non-delivery Notification).

Primary and Copy Recipients Indication
      Supported

Probe
      Supported at the gateway (i.e., the gateway services the
      probe).

Probe Origin Authentication
      N/A (reception).

Proof of Delivery
      Not supported.

Proof of Submission
      N/A (local).

Receipt Notification Request Indication
      Not supported.

Redirection Allowed by Originator
      Redirection means MTS supported redirection, in the manner
      of X.400.  This service does not exist in the RFC 822 world.
      RFC 822 redirection (e.g., aliasing) should be regarded as
      an informal redirection mechanism, beyond the scope of this
      control.  Messages will be sent to RFC 822, irrespective of
      whether this service is requested.  Theoretically therefore,
      this service is supported, although in practice it may
      appear that it is not supported.

Registered Mail
      N/A (PDAU).

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Registered Mail to Addressee in Person
      N/A (PDAU).

Reply Request Indication
      Supported as comment next to address.

Replying IP Message Indication
      Supported.

Report Origin Authentication
      N/A (reception).

Request for Forwarding Address
      N/A (PDAU).

Requested Delivery Method
      N/A (local).   The services required must be dealt with at
      submission time.  Any such request is made available through
      the gateway by use of a comment associated with the
      recipient in question.

Return of Content
      In principle, this is N/A, as non-delivery notifications are
      not supported.  In practice, most RFC 822 systems will
      return part or all of the content along with the IP Message
      indicating an error (see Non-delivery Notification).

Sensitivity Indication
      Supported as new RFC 822 header (Sensitivity:).

Special Delivery
      N/A (PDAU).

Stored Message Deletion
      N/A (MS).

Stored Message Fetching
      N/A (MS).

Stored Message Listing
      N/A (MS).

Stored Message Summary
      N/A (MS).

Subject Indication
      Supported.

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Undeliverable Mail with Return of Physical Message
      N/A (PDAU).

Use of Distribution List
      In principle this applies only to X.400 supported
      distribution lists (see DL Expansion Prohibited).
      Theoretically, this service is N/A (prior).  In practice,
      because of informal RFC 822 lists, this service can be
      regarded as supported.

2.3.2.  Reception by X.400

2.3.2.1.  Standard Mandatory Services

   The following standard IPM mandatory  user facilities are required
   for reception of RFC 822 originated mail by an X.400 UA.

   Content Type Indication

   Delivery Time Stamp Indication

   IP Message Identification

   Message Identification

   Non-delivery Notification

   Original Encoded Information Types Indication

   Submission Time Stamp Indication

   Typed Body

2.3.2.2.  Standard Optional Services

   The following standard IPM optional user facilities are required for
   reception of RFC 822 originated mail by an X.400 UA.

   Authorising User's Indication

   Blind Copy Recipient Indication

   Cross Referencing Indication

   Originator Indication

   Primary and Copy Recipients Indication

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   Replying IP Message Indication

   Subject Indication

2.3.2.3.  New Services

   A new service "RFC 822 Header Field" is defined using the extension
   facilities.  This allows for any RFC 822 header field to be
   represented.  It may be present in RFC 822 originated messages, which
   are received by an X.400 UA.



(page 24 continued on part 2)

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