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RFC 1148

Pages: 94
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Mapping between X.400(1988) / ISO 10021 and RFC 822

Part 1 of 3, p. 1 to 29
None       Next RFC Part

Obsoleted by:    2156    1327
Updates:    1026    0987    1138    0822

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Network Working Group                                           S. Kille
Request for Comments 1148                      University College London
Updates: RFCs 822, 987, 1026, 1138                            March 1990

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

Status of this Memo

   This RFC suggests an electronic mail protocol mapping for the
   Internet community and UK Academic Community, and requests discussion
   and suggestions for improvements.  This memo does not specify an
   Internet standard.  This edition includes material lost in editing.
   Distribution of this memo is unlimited.

   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 based on RFC 987 and RFC 1026 [Kille86a, Kille87a],
   which define a similar mapping for X.400 (1984).  This document does
   not obsolete the earlier ones, as its domain of application is


   This document specifies a mapping between two protocols.  This
   specification should be used when this mapping is performed on the
   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 ...............................................    2
   1.1  X.400 .................................................    2
   1.2  RFC 822 ...............................................    3
   1.3  The need for conversion ...............................    4
   1.4  General approach ......................................    4
   1.5  Gatewaying Model ......................................    5
   1.6  RFC 987 ...............................................    7
   1.7  Aspects not covered ...................................    8
   1.8  Subsetting ............................................    9

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   1.9  Document Structure ....................................    9
   1.10  Acknowledgements .....................................   10
   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 .........................................   25
   3.3  Standard Types ........................................   25
   3.4  Encoding ASCII in Printable String ....................   28
   4.  Addressing .............................................   29
   4.1  A textual representation of MTS.ORAddress .............   30
   4.2  Basic Representation ..................................   30
   4.3  EBNF.822-address <-> MTS.ORAddress ....................   34
   4.4  Repeated Mappings .....................................   43
   4.5  Directory Names .......................................   45
   4.6  MTS Mappings ..........................................   45
   4.7  IPMS Mappings ....... .................................   48
   5.  Detailed Mappings ......................................   52
   5.1  RFC 822 -> X.400 ......................................   52
   5.2  Return of Contents ....................................   59
   5.3  X.400 -> RFC 822 ......................................   60
   Appendix A  Differences with RFC 987 .......................   79
   1.  Introduction ...........................................   79
   2.  Service Elements .......................................   80
   3.  Basic Mappings .........................................   80
   4.  Addressing .............................................   80
   5.  Detailed Mappings ......................................   80
   6.  Appendices .............................................   81
   Appendix B  Mappings specific to the JNT Mail ..............   81
   1.  Introduction ...........................................   81
   2.  Domain Ordering ........................................   81
   3.  Acknowledge-To: ........................................   81
   4.  Trace ..................................................   82
   5.  Timezone specification .................................   82
   6.  Lack of 822-MTS originator specification ...............   82
   Appendix C  Mappings specific to UUCP Mail .................   83
   Appendix D  Object Identifier Assignment ...................   83
   Appendix E  BNF Summary ....................................   84
   Appendix F  Format of address mapping tables ...............   91
   References .................................................   92

Chapter 1 -- Overview

1.1.  X.400

   This document relates to the CCITT 1988 X.400 Series Recommendations

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    / 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 is the current specification of the messaging standard on the
   Internet.  This standard evolved with the evolution of the network
   from the ARPANET (created by the Defense Advanced Research Projects
   Agency) to the Internet, which now involves over 1000 networks and is
   sponsored by DARPA, NSF, DOE, NASA, and NIH.  It specifies an end to
   end message format.  It is used in conjunction with a number of
   different message transfer protocol environments.

      SMTP Networks

         On the 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 1034
         which is a Specification for domains and a distributed name
         service [Mockapetris87a].

      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 1034, but not the corresponding domain nameservers


         Some portions of Csnet follow the Internet protocols.  The
         dialup portion of Csnet uses the Phonenet protocols as a
         replacement for RFC 821.  This portion uses domains which
         conform to RFC 1034, but not the corresponding domain


         Some parts of Bitnet and related networks 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 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.

      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

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           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.   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

      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.

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

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   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 define 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
   or MTA Service Elements.

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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 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).
   In particular, there is no expectation of additional X.400 services
   being mapped - although this may be possible in some cases.

1.6.  RFC 987

   Much of this work is based on the initial specification of RFC 987
   and in its addendum RFC 1026.  A basic decision is that the mapping
   will be to the full 1988 version of X.400, and not to a 1984
   compatible subset.  This is important, to give good support to
   communities which will utilise full X.400 at an early date.  This has

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   the following implications:

      -    This document does not obsolete RFC 987, as it has a
           different domain of application.

      -    If a gatewayed message is being transferred to a 1984
           system, then RFC 987 should be used.  If the X.400 side of
           the gateway is a 1988 system, then it should be operated in
           1984 compatibility mode.  There is no advantage and some
           disadvantage in using the new mapping, and later on applying
           X.400 downgrading rules.  Note that in an environment where
           RFC 822 is of major importance, it may be desirable for
           downgrading to consider the case where the message was
           originated in an RFC 822 system, and mapped according to
           this specification.

      -    New features of X.400 can be used to provide a much cleaner
           mapping than that defined in RFC 987.

   Unnecessary change is usually a bad idea.  Changes on the RFC 822
   side are avoided as far as possible, so that RFC 822 users do not see
   arbitrary differences between systems conforming to this
   specification, and those following RFC 987.  Changes on the X.400
   side are minimised, but are more acceptable, due to the mapping onto
   a new set of services and protocols.

   A summary of changes made is given in Appendix A.

1.7.  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

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

      -    X.400 user interface definition

   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 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

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   specification targeted at X.400, without RFC 822 restrictions, would
   be more appropriate.

1.8.  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

1.9.  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

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

   There are also six appendices:

      A.   Differences with RFC 987

      B.   Mappings Specific to JNT Mail

      C.   Mappings Specific to UUCP Mail

      D.   Object Identifier Assignment

      E.   BNF Summary

      F.   Format of Address Tables



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1.10.  Acknowledgements

   This work was partly sponsored by the Joint Network Team.  The
   workshop at UCL in June 1989 to work on this specification was also
   an IFIP WG 6.5 meeting.

   The work in this specification was substantially based on RFC 987,
   which had input from many people.

   Useful comments and suggestions were made by Pete Cowen (Nottingham
   Univ), Jim Craigie (JNT), Christian Huitema (Inria), Peter Lynch
   (Prime), Julian Onions (Nottingham Univ), Sandy Shaw (Edinburgh
   Univ), Einar Stefferud (NMA), and Peter Sylvester (GMD).

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:

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

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

      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
   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.

   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

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

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   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).
   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
   should require that their X.400 User Agents are able to display these
   heading extensions.  Support for the various service elements
   (headers) is now listed.


           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



      To:  Supported.

      Cc:  Supported.

      Bcc: Supported.


           Supported, for a single reference.  Where multiple
           references are given, partial support is given by mapping to
           "Cross Referencing Indication".  This gives similar


           Supported by use of a heading extension.

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           Supported by use of an extra body part.

           Supported by use of a heading extension.

           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











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   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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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

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

      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

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      Submission Time Stamp Indication

      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
           will only be done where content conversion is not

      User Capabilities Registration
           N/A (local).  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

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

      Basic Physical Rendition
           N/A (PDAU).

      Blind Copy Recipient Indication

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      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

      Content Confidentiality
           Not supported.

      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

      Counter Collection
           N/A (PDAU).

      Counter Collection with Advice
           N/A (PDAU).

      Cross Referencing Indication

      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).

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      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.

      DL Expansion History Indication
           Supported by use of a new RFC 822 header

      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

      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:).

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      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.

      Message Origin Authentication
            N/A (reception).

      Message Security Labelling
            Not supported.

      Message Sequence Integrity
            Not supported.

      Multi-Destination Delivery

      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

      Originator Requested Alternate Recipient
            Not supported, but is placed as comment next to address

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

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

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

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

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

      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,

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            this service is supported, although in practice it may
            appear that it is not supported.

      Registered Mail
            N/A (PDAU).

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

      Reply Request Indication
            Supported as comment next to address.

      Replying IP Message Indication

      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).

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      Stored Message Summary
            N/A (MS).

      Subject Indication

      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  Standard Mandatory Services

   The following standard IPM mandatory user facilities may be 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  Standard Optional Services

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

      Authorising User's Indication

      Blind Copy Recipient Indication

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      Cross Referencing Indication

      Originator Indication

      Primary and Copy Recipients Indication

      Replying IP Message Indication

      Subject Indication  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.

Chapter 3 -- Basic Mappings

3.1.  Notation

   The X.400 protocols are encoded in a structured manner according to
   ASN.1, whereas RFC 822 is text encoded.  To define a detailed
   mapping, it is necessary to refer to detailed protocol elements in
   each format.  A notation to achieve this is described in this

3.1.1.  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 "822." appended to the beginning of the string (e.g.,
   822.addr-spec).  Additional syntax rules, to be used throughout this
   specification, are defined in this chapter.

   The EBNF is used in two ways.

      1.   To describe components of RFC 822 messages (or of 822-MTS
           components).  In this case, the lexical analysis defined in
           Section 3 of RFC 822 should be used.  When these new EBNF
           tokens are referred to outside an EBNF definition, they are
           identified by the string "EBNF." appended to the beginning
           of the string (e.g., EBNF.bilateral-info).

      2.   To describe the structure of IA5 or ASCII information not in

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           an RFC 822 message.  In these cases, tokens will either be
           self delimiting, or be delimited by self delimiting tokens.
           Comments and LWSP are not used as delimiters.

3.1.2.  ASN.1

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

      element         = service "." definition *( "." definition )
      service         = "IPMS" / "MTS" / "MTA"
      definition      = identifier / context
      identifier      = ALPHA *< ALPHA or DIGIT or "-" >
      context         = "[" 1*DIGIT "]"

   The EBNF.service keys are shorthand for the following service

      IPMS IPMSInformationObjects defined in Annex E of X.420 / ISO

      MTS  MTSAbstractService defined in Section 9 of X.411 / ISO

      MTA  MTAAbstractService defined in Section 13 of X.411 / ISO

   The first EBNF.identifier identifies a type or value key in the
   context of the defined service specification.   Subsequent
   EBNF.identifiers identify a value label or type in the context of the
   first identifier (SET or SEQUENCE).  EBNF.context indicates a context
   tag, and is used where there is no label or type to uniquely identify
   a component.  The special EBNF.identifier keyword "value" is used to
   denote an element of a sequence.

   For example, IPMS.Heading.subject defines the subject element of the
   IPMS heading.  The same syntax is also used to refer to element
   values.  For example, MTS.EncodedInformationTypes.[0].g3Fax refers to
   a value of MTS.EncodedInformationTypes.[0].

3.2.  ASCII and IA5

   A gateway will interpret all IA5 as ASCII.  Thus, mapping between
   these forms is conceptual.

3.3.  Standard Types

   There is a need to convert between ASCII text, and some of the types
   defined in ASN.1 [CCITT/ISO88d].  For each case, an EBNF syntax

Top      ToC       Page 26 
   definition is given, for use in all of this specification, which
   leads to a mapping between ASN.1, and an EBNF construct.

   All EBNF syntax definitions of ASN.1 types are in lower case, whereas
   ASN.1 types 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-restricted-char      = 1DIGIT /  1ALPHA / " " / "'" / "+"
                         / "," / "-" / "." / "/" / ":" / "=" / "?"
      ps-delim         = "(" / ")"
      ps-char          = ps-delim / ps-restricted-char

   This can be used to represent real printable strings in EBNF.

3.3.4.  T.61String

   In cases where T.61 strings are only used for conveying human
   interpreted information, the aim of a mapping should be to render the
   characters appropriately in the remote character set, rather than to
   maximise reversibility.  For these cases, the mappings to IA5 defined
   in CCITT Recommendation X.408 (1988) should be used [CCITT/ISO88a].
   These will then be encoded in ASCII.

   There is also a need to represent Teletex Strings in ASCII, for some
   aspects of O/R Address.  For these, the following encoding is used:

      teletex-string   = *( ps-char / t61-encoded )
      t61-encoded      = "{" 1* t61-encoded-char "}"
      t61-encoded-char = 3DIGIT

   Common characters are mapped simply.  Other octets are mapped using a

Top      ToC       Page 27 
   quoting mechanism similar to the printable string mechanism.  Each
   octet is represented as 3 decimal digits.

   There are a number of places where a string may have a Teletex and/or
   Printable String representation.  The following BNF is used to
   represent this.

   teletex-and-or-ps = [ printablestring ] [ "*" teletex-string ]

   The natural mapping is restricted to, in order to make
   the full BNF easier to parse.

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.

        In practice, a gateway will need to parse various illegal
        variants on  In cases where
        cannot be parsed, it is recommended that the derived UTCTime
        is set to the value at the time of translation.

   The UTCTime format which specifies the timezone offset should be

3.3.6.  Integer

   A basic ASN.1 Integer will be mapped onto EBNF.numericstring.  In many
   cases ASN.1 will enumerate Integer values or use ENUMERATED.  An EBNF
   encoding labelled-integer is provided. When mapping from EBNF to
   ASN.1, only the integer value is mapped, and the associated text is
   discarded.  When mapping from ASN.1 to EBNF, addition of an
   appropriate text label is strongly encouraged.

      labelled-integer ::= [ key-string ] "(" numericstring ")"

      key-string      = *key-char
      key-char        = <a-z, A-Z, 1-9, and "-">

3.3.7.  Object Identifier

   Object identifiers are represented in a form similar to that
   given in ASN.1.  The numbers are mandatory, to ease encoding.
   It is recommended that as many strings as possible are used, to

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   facilitate user recognition.

      object-identifier ::= [ defined-value ] oid-comp-list

      oid-comp-list ::= oid-comp oid-comp-list
                      | oid-comp

      defined-value ::= key-string

      oid-comp ::= [ key-string ] "(" numericstring ")"

3.4.  Encoding ASCII in Printable String

   Some information in RFC 822 is represented in ASCII, and needs to be
   mapped into X.400 elements encoded as printable string.  For this
   reason, a mechanism to represent ASCII encoded as PrintableString is

   A structured subset of EBNF.printablestring is now defined.  This can
   be used to encode ASCII in the PrintableString character set.

      ps-encoded       = *( ps-restricted-char / ps-encoded-char )
      ps-encoded-char  = "(a)"               ; (@)
                       / "(p)"               ; (%)
                       / "(b)"               ; (!)
                       / "(q)"               ; (")
                       / "(u)"               ; (_)
                       / "(l)"               ; "("
                       / "(r)"               ; ")"
                       / "(" 3DIGIT ")"

   The 822.3DIGIT in must have range 0-127, and is
   interpreted in decimal as the corresponding ASCII character.  Special
   encodings are given for: at sign (@), percent (%), exclamation
   mark/bang (!), double quote ("), underscore (_), left bracket ((),
   and right bracket ()).  These characters, with the exception of round
   brackets, 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.  These special encodings should be
   mapped in a case insensitive manner, but always be generated in lower

   A reversible mapping between PrintableString and ASCII can now be
   defined.  The reversibility means that some values of printable
   string (containing round braces) cannot be generated from ASCII.
   Therefore, this mapping must only be used in cases where the
   printable strings may only be derived from ASCII (and will therefore
   have a restricted domain).  For example, in this specification, it is

Top      ToC       Page 29 
   only applied to a Domain defined attribute which will have been
   generated by use of this specification and a value such as "(" would
   not be possible.

   To encode ASCII as PrintableString, the syntax is
   used, with all mapped directly.  All other
   822.CHAR are encoded as

   To encode PrintableString as ASCII, parse PrintableString as, and then reverse the previous mapping.  If the
   PrintableString cannot be parsed, then the mapping is being applied
   in to an inappropriate value, and an error should be given to the
   procedure doing the mapping. In some cases, it may be preferable to
   pass the printable string through unaltered.

   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)               <->   @
                   (l)a(r)           <->   (a)
                   (126)             <->   ~
                   (                  ->   (
                   (l)               <->   (

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 textual representation of an X.400 O/R

   Initially, we consider an address in the (human) mail user sense of
   "what is typed at the mailsystem to reference a mail user".  A basic
   RFC 822 address is defined by the EBNF EBNF.822-address:

                822-address     = [ route ] addr-spec

   In an 822-MTS 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.

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