path: root/doc/rfc/rfc1148.txt

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
   different.

Specification

   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
         [Horton86a].

      Csnet

         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
         nameservers.

      Bitnet

         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
         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.

      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
   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.

   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
   specify:

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

      -    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
   discouraged.

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
           component.

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

   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

   WARNING:

      THE REMAINDER OF THIS SPECIFICATION IS TECHNICALLY DETAILED.
      IT WILL NOT MAKE SENSE, EXCEPT IN THE CONTEXT OF RFC 822 AND



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      X.400 (1988).  DO NOT ATTEMPT TO READ THIS DOCUMENT UNLESS
      YOU ARE FAMILIAR WITH THESE SPECIFICATIONS.

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:

      Supported
         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
         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
   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
   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



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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.

      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.



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      Subject:
           Supported.

      Comments:
           Supported by use of an extra body part.

      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:




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      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):

      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:

      Redirection-History:

      Reply-By:

      Requested-Delivery-Method:



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      Sensitivity:

      X400-Content-Type:

      X400-MTS-Identifier:

      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.







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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.

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:).



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      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
           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.




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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
           question.

      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
           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).




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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-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:).



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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
            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:).




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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
            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,



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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
            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).




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      Stored Message Summary
            N/A (MS).

      Subject Indication
            Supported.

      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 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

2.3.2.2.  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

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.

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
   section.

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
   specifications:

      IPMS IPMSInformationObjects defined in Annex E of X.420 / ISO
           10021-7.

      MTS  MTSAbstractService defined in Section 9 of X.411 / ISO
           10021-4.

      MTA  MTAAbstractService defined in Section 13 of X.411 / ISO
          10021-4.

   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



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   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



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   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 EBNF.ps-char, in order to make
   the full BNF easier to parse.

3.3.5.  UTCTime

   Both UTCTime and the RFC 822 822.date-time syntax contain:  Year
   (lowest two digits), Month, Day of Month, hour, minute, second
   (optional), and Timezone.  822.date-time also contains an optional
   day of the week, but this is redundant.  Therefore a symmetrical
   mapping can be made between these constructs.

   Note:
        In practice, a gateway will need to parse various illegal
        variants on 822.date-time.  In cases where 822.date-time
        cannot be parsed, it is recommended that the derived UTCTime
        is set to the value at the time of translation.

   The UTCTime format which specifies the timezone offset should be
   used.

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
   needed.

   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 EBNF.ps-encoded-char 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
   case.

   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



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   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 EBNF.ps-encoded syntax is
   used, with all EBNF.ps-restricted-char mapped directly.  All other
   822.CHAR are encoded as EBNF.ps-encoded-char.

   To encode PrintableString as ASCII, parse PrintableString as
   EBNF.ps-encoded, 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
   Address.

   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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   The basic X.400 O/R Address, used by the MTS for routing, is defined
   by MTS.ORAddress.  In IPMS, the MTS.ORAddress is encapsulated within
   IPMS.ORDescriptor.

   It can be seen that RFC 822 822.address must be mapped with
   IPMS.ORDescriptor, and that RFC 822 EBNF.822-address must be mapped
   with MTS.ORAddress.

4.1.  A textual representation of MTS.ORAddress

   MTS.ORAddress is structured as a set of attribute value pairs.  It is
   clearly necessary to be able to encode this in ASCII for gatewaying
   purposes.  All aspects should be encoded, in order to guarantee
   return of error messages, and to optimise third party replies.

4.2.  Basic Representation

   An O/R Address has a number of structured and unstructured
   attributes.  For each unstructured attribute, a key and an encoding
   is specified.  For structured attributes, the X.400 attribute is
   mapped onto one or more attribute value pairs.  For domain defined
   attributes, each element of the sequence will be mapped onto a triple
   (key and two values), with each value having the same encoding.  The
   attributes are as follows, with 1984 attributes given in the first
   part of the table.  For each attribute, a reference is given,
   consisting of the relevant sections in X.402 / ISO 10021-2, and the
   extension identifier for 88 only attributes:

Attribute (Component)               Key            Enc     Ref       Id

84/88 Attributes

MTS.CountryName                     C              P       18.3.3
MTS.AdministrationDomainName        ADMD           P       18.3.1
MTS.PrivateDomainName               PRMD           P       18.3.21
MTS.NetworkAddress                  X121           N       18.3.7
MTS.TerminalIdentifier              T-ID           N       18.3.23
MTS.OrganizationName                O              P/T     18.3.9
MTS.OrganizationalUnitNames.value   OU             P/T     18.3.10
MTS.NumericUserIdentifier           UA-ID          N       18.3.8
MTS.PersonalName                    PN             P/T     18.3.12
MTS.PersonalName.surname            S              P/T     18.3.12
MTS.PersonalName.given-name         G              P/T     18.3.12
MTS.PersonalName.initials           I              P/T     18.3.12
MTS.PersonalName
   .generation-qualifier            GQ             P/T     18.3.12
MTS.DomainDefinedAttribute.value    DD             P/T     18.1




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88 Attributes

MTS.CommonName                      CN             P/T     18.3.2    1
MTS.TeletexCommonName               CN             P/T     18.3.2    2
MTS.TeletexOrganizationName         O              P/T     18.3.9    3
MTS.TeletexPersonalName             PN             P/T     18.3.12   4
MTS.TeletexPersonalName.surname     S              P/T     18.3.12   4
MTS.TeletexPersonalName.given-name  G              P/T     18.3.12   4
MTS.TeletexPersonalName.initials    I              P/T     18.3.12   4
MTS.TeletexPersonalName
   .generation-qualifier            GQ             P/T     18.3.12   4
MTS.TeletexOrganizationalUnitNames
   .value                           OU             P/T     18.3.10   5
MTS.TeletexDomainDefinedAttribute
   .value                           DD             P/T     18.1      6
MTS.PDSName                         PD-SYSTEM      P       18.3.11   7
MTS.PhysicalDeliveryCountryName     PD-C           P       18.3.13   8
MTS.PostalCode                      POSTCODE       P       18.3.19   9
MTS.PhysicalDeliveryOfficeName      PD-OFFICE      P/T     18.3.14  10
MTS.PhysicalDeliveryOfficeNumber    PD-OFFICE-NUM  P/T     18.3.15  11
MTS.ExtensionORAddressComponents    PD-EXT-D       P/T     18.3.4   12
MTS.PhysicalDeliveryPersonName      PD-PN          P/T     18.3.17  13
MTS.PhysicalDelivery                PD-O           P/T     18.3.16  14
   OrganizationName
MTS.ExtensionPhysicalDelivery
   AddressComponents                PD-EXT-LOC     P/T     18.3.5   15
MTS.UnformattedPostalAddress        PD-ADDRESS     P/T     18.3.25  16
MTS.StreetAddress                   STREET         P/T     18.3.22  17
MTS.PostOfficeBoxAddress            PO-BOX         P/T     18.3.18  18
MTS.PosteRestanteAddress            POSTE-RESTANTE P/T     18.3.20  19
MTS.UniquePostalName                PD-UNIQUE      P/T     18.3.26  20
MTS.LocalPostalAttributes           PD-LOCAL       P/T     18.3.6   21
MTS.ExtendedNetworkAddress
   .e163-4-address.number           NET-NUM        N       18.3.7   22
MTS.ExtendedNetworkAddress
   .e163-4-address.sub-address      NET-SUB        N       18.3.7   22
MTS.ExtendedNetworkAddress
  .psap-address                     NET-PSAP       X       18.3.7   22
MTS.TerminalType                    NET-TTYPE      I       18.3.24  23

   The following keys identify different EBNF encodings, which are
   associated with the ASCII representation of MTS.ORAddress.

                 Key         Encoding

                 P     printablestring
                 N     numericstring
                 T     teletex-string



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                 P/T   teletex-and-or-ps
                 I     labelled-integer
                 X     presentation-address

   The BNF for presentation-address is taken from the specification "A
   String Encoding of Presentation Address" [Kille89a].

   In most cases, the EBNF encoding maps directly to the ASN.1 encoding
   of the attribute.  There are a few exceptions. In cases where an
   attribute can be encoded as either a PrintableString or NumericString
   (Country, ADMD, PRMD), either form should be mapped into the BNF.
   When generating ASN.1, the NumericString encoding should be used if
   the string contains only digits.

   There are a number of cases where the P/T (teletex-and-or-ps)
   representation is used.  Where the key maps to a single attribute,
   this choice is reflected in the encoding of the attribute (attributes
   10-21).  For most of the 1984 attributes and common name, there is a
   printablestring and a teletex variant.   This pair of attributes is
   mapped onto the single component here.  This will give a clean
   mapping for the common cases where only one form of the name is used.

4.2.1.  Encoding of Personal Name

   Handling of Personal Name and Teletex Personal Name based purely on
   the EBNF.standard-type syntax defined above is likely to be clumsy.
   It seems desirable to utilise the "human" conventions for encoding
   these components.  A syntax is defined, which is designed to provide
   a clean encoding for the common cases of O/R address specification
   where:

      1.   There is no generational qualifier

      2.   Initials contain only letters

      3.   Given Name does not contain full stop ("."), and is at least
           two characters long.

      4.   If Surname contains full stop, then it may not be in the
           first two characters, and either initials or given name is
           present.

   The following EBNF is defined:

                encoded-pn      = [ given "." ] *( initial "." ) surname

                given           = 2*<ps-char not including ".">




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                initial         = ALPHA

                surname         = printablestring

   This can be used to map from any string containing only printable
   string characters to an O/R address personal name. Parse the string
   according to the EBNF.  The given name and surname are assigned
   directly.  All EBNF.initial tokens are concatenated without
   intervening full stops to generate the initials.

   For an O/R address which follows the above restrictions, a string can
   be derived in the natural manner.  In this case, the mapping will be
   reversible.

        For example:

                GivenName       = "Marshall"
                Surname         = "Rose"

                Maps with  "Marshall.Rose"

                Initials        = "MT"
                Surname         = "Rose"

                Maps with  "M.T.Rose"

                GivenName       = "Marshall"
                Initials        = "MT"
                Surname         = "Rose"

                Maps with  "Marshall.M.T.Rose"
   Note that X.400 suggest that Initials is used to encode ALL initials.
   Therefore, the proposed encoding is "natural" when either GivenName
   or Initials, but not both, are present.  The case where both are
   present can be encoded, but this appears to be contrived!

4.2.2.  Standard Encoding of MTS.ORAddress

   Given this structure, we can specify a BNF representation of an O/R
   Address.

                std-or-address  = 1*( "/" attribute "=" value ) "/"
                attribute       = standard-type
                                / "RFC-822"
                                / registered-dd-type
                                / dd-key "." std-printablestring

                standard-type   = key-string



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                registered-dd-type
                                = key-string
                dd-key          = key-string

                value           = std-printablestring

                std-printablestring
                                = *( std-char / std-pair )
                std-char        = <"{", "}", "*", and any ps-char
                                                except "/" and "=">
                std-pair        = "$" ps-char

   The standard-type is any key defined in the table in Section 4.2,
   except PN, and DD.  The value, after quote removal, should be
   interpreted according to the defined encoding.

   If the standard-type is PN, the value is interpreted according to
   EBNF.encoded-pn, and the components of MTS.PersonalName and/or
   MTS.TeletexPersonalName derived accordingly.

   If dd-key is the recognised Domain Defined string (DD), then the type
   and value should be interpreted according to the syntax implied from
   the encoding, and aligned to either the teletex or printable string
   form.  Key and value should have the same encoding.

   If value is "RFC-822", then the (printable string) Domain Defined
   Type of "RFC-822" is assumed.  This is an optimised encoding of the
   domain defined type defined by this specification.

   The matching of all keywords should be done in a case- independent
   manner.

   If the value is registered-dd-type, the value is registered with the
   IANA and will be listed in the Assigned Numbers RFC, then the value
   should be interpreted accordingly.  This restriction maximises the
   syntax checking which can be done at a gateway.

4.3.  EBNF.822-address <-> MTS.ORAddress

   Ideally, the mapping specified would be entirely symmetrical and
   global, to enable addresses to be referred to transparently in the
   remote system, with the choice of gateway being left to the Message
   Transfer Service.  There are two fundamental reasons why this is not
   possible:

      1.   The syntaxes are sufficiently different to make this
           awkward.




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      2.   In the general case, there would not be the necessary
           administrative co-operation between the X.400 and RFC 822
           worlds, which would be needed for this to work.

   Therefore, an asymmetrical mapping is defined, which can be
   symmetrical where there is appropriate administrative control.

4.3.1.  X.400 encoded in RFC 822

   The std-or-address syntax is  used to encode O/R Address information
   in the 822.local-part of EBNF.822-address.  Further O/R Address
   information may be associated with the 822.domain component.  This
   cannot be used in the general case, basically due to character set
   problems, and lack of order in X.400 O/R Addresses.  The only way to
   encode the full PrintableString character set in a domain is by use
   of the 822.domain-ref syntax (i.e., 822.atom).  This is likely to
   cause problems on many systems.  The effective character set of
   domains is in practice reduced from the RFC 822 set, by restrictions
   imposed by domain conventions and policy.

   A generic 822.address consists of a 822.local-part and a sequence of
   822.domains (e.g., <@domain1,@domain2:user@domain3>).  All except the
   822.domain associated with the 822.local-part (domain3 in this case)
   should be considered to specify routing within the RFC 822 world, and
   will not be interpreted by the gateway (although they may have
   identified the gateway from within the RFC 822 world).

      This form of source routing is now discouraged in the Internet
      (Host Requirements, page 58 [Braden89a]).

   The 822.domain associated with the 822.local-part may also identify
   the gateway from within the RFC 822 world.  This final 822.domain may
   be used to determine some number of O/R Address attributes.  The
   following O/R Address attributes are considered as a hierarchy, and
   may be specified by the domain.  They are (in order of hierarchy):

      Country, ADMD, PRMD, Organisation, Organisational Unit

      There may be multiple Organisational Units.

      Associations may be defined between domain specifications, and
      some set of attributes.  This association proceeds hierarchically.
      For example, if a domain implies ADMD, it also implies country.
      Subdomains under this are associated according to the O/R Address
      hierarchy.  For example:

      => "AC.UK" might be associated with
      C="GB", ADMD="GOLD 400", PRMD="UK.AC"



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      then domain "R-D.Salford.AC.UK" maps with
      C="GB", ADMD="GOLD 400", PRMD="UK.AC", O="Salford", OU="R-D"

      There are three basic reasons why a domain/attribute mapping might
      be maintained, as opposed to using simply subdomains:

      1.   As a shorthand to avoid redundant X.400 information.  In
           particular, there will often be only one ADMD per country,
           and so it does not need to be given explicitly.

      2.   To deal with cases where attribute values do not fit the
           syntax:

              domain-syntax   = alphanum [ *alphanumhyphen alphanum ]
              alphanum        = <ALPHA or DIGIT>
              alphanumhyphen  = <ALPHA or DIGIT or HYPHEN>

           Although RFC 822 allows for a more general syntax, this
           restricted syntax is chosen as it is the one chosen by the
           various domain service administrations.

      3.   To deal with missing elements in the hierarchy.  A domain
           may be associated with an omitted attribute in conjunction
           with several present ones.  When performing the algorithmic
           insertion of components lower in the hierarchy, the omitted
           value should be skipped.  For example, if "HNE.EGM" is
           associated with "C=TC", "ADMD=ECQ", "PRMD=HNE", and omitted
           organisation, then "ZI.HNE.EGM" is mapped with "C=TC",
           "ADMD=ECQ", "PRMD=HNE", "OU=ZI". It should be noted that
           attributes may have null values, and that this is treated
           separately from omitted attributes (whilst it would be bad
           practice to treat these two cases differently, they must be
           allowed for).

   This set of mappings need only be known by the gateways relaying
   between the RFC 822 world, and the O/R Address space associated with
   the mapping in question.  However, it is desirable (for the optimal
   mapping of third party addresses) for all gateways to know these
   mappings.  A format for the exchange of this information is defined
   in Appendix F.

   The remaining attributes are encoded on the LHS, using the EBNF.std-
   or-address syntax.  For example:

                /I=J/S=Linnimouth/GQ=5/@Marketing.Widget.COM

   encodes the MTS.ORAddress consisting of:




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                MTS.CountryName                       = "TC"
                MTS.AdministrationDomainName          = "BTT"
                MTS.OrganizationName                  = "Widget"
                MTS.OrganizationalUnitNames.value     = "Marketing"
                MTS.PersonalName.surname              = "Linnimouth"
                MTS.PersonalName.initials             = "J"
                MTS.PersonalName.generation-qualifier = "5"

   The first three attributes are determined by the domain Widget.COM.
   Then, the first element of OrganizationalUnitNames is determined
   systematically, and the remaining attributes are encoded on the LHS.
   In an extreme case, all of the attributes will be on the LHS.  As the
   domain cannot be null, the RHS will simply be a domain indicating the
   gateway.

   The RHS (domain) encoding is designed to deal cleanly with common
   addresses, and so the amount of information on the RHS should be
   maximised.  In particular, it covers the Mnemonic O/R Address using a
   1984 compatible encoding.  This is seen as the dominant form of O/R
   Address.  Use of other forms of O/R Address, and teletex encoded
   attributes will require an LHS encoding.

   There is a further mechanism to simplify the encoding of common
   cases, where the only attributes to be encoded on the LHS is a (non-
   Teletex) Personal Name attributes which comply with the restrictions
   of 4.2.1.  To achieve this, the 822.local-part shall be encoded as
   EBNF.encoded-pn.  In the previous example, if the GenerationQualifier
   was not present, the encoding J.Linnimouth@Marketing.Widget.COM would
   result.

   From the standpoint of the RFC 822 Message Transfer System, the
   domain specification is simply used to route the message in the
   standard manner.  The standard domain mechanisms are are used to
   select appropriate gateways for the corresponding O/R Address space.
   In most cases, this will be done by registering the higher levels,
   and assuming that the gateway can handle the lower levels.

4.3.2.  RFC 822 encoded in X.400

   In some cases, the encoding defined above may be reversed, to give a
   "natural" encoding of genuine RFC 822 addresses.  This depends
   largely on the allocation of appropriate management domains.

   The general case is mapped by use of domain defined attributes.  A
   Domain defined type "RFC-822" is defined.  The associated attribute
   value is an ASCII string encoded according to Section 3.3.3 of this
   specification.  The interpretation of the ASCII string depends on the
   context of the gateway.



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      1.   In the context of RFC 822, and RFC 1034
           [Crocker82a, Mockapetris87a], the string can be used
           directly.

      2.   In the context of the JNT Mail protocol, and the NRS
           [Kille84a, Larmouth83a], the string should be interpreted
           according to Mailgroup Note 15 [Kille84b].

      3.   In the context of UUCP based systems, the string should be
           interpreted as defined in [Horton86a].

   Other O/R Address attributes will be used to identify a context in
   which the O/R Address will be interpreted.  This might be a
   Management Domain, or some part of a Management Domain which
   identifies a gateway MTA.  For example:

                C               = "GB"
                ADMD            = "GOLD 400"
                PRMD            = "UK.AC"
                O               = "UCL"
                OU              = "CS"
                "RFC-822"      =  "Jimmy(a)WIDGET-LABS.CO.UK"

        OR

                C               = "TC"
                ADMD            = "Wizz.mail"
                PRMD            = "42"
                "rfc-822"       = "Postel(a)venera.isi.edu"

   Note in each case the PrintableString encoding of "@" as "(a)".  In
   the second example, the "RFC-822" domain defined attribute is
   interpreted everywhere within the (Private) Management Domain.  In
   the first example, further attributes are needed within the
   Management Domain to identify a gateway.  Thus, this scheme can be
   used with varying levels of Management Domain co-operation.

4.3.3.  Component Ordering

   In most cases, ordering of O/R Address components is not significant
   for the mappings specified.  However, Organisational Units (printable
   string and teletex forms) and Domain Defined Attributes are specified
   as SEQUENCE in MTS.ORAddress, and so their order may be significant.
   This specification needs to take account of this:

      1.   To allow consistent mapping into the domain hierarchy

      2.   To ensure preservation of order over multiple mappings.



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There are three places where an order must be specified:

   1.   The text encoding (std-or-address) of MTS.ORAddress as used
        in the local-part of an RFC 822 address.  An order is needed
        for those components which may have multiple values
        (Organisational Unit, and Domain Defined Attributes). When
        generating an 822.std-or-address, components of a given type
        shall be in hierarchical order with the most significant
        component on the RHS.  If there is an Organisation
        Attribute, it shall be to the right of any Organisational
        Unit attributes.  These requirements are for the following
        reasons:

        -    Alignment to the hierarchy of other components in RFC
             822 addresses (thus, Organisational Units will appear
             in the same order, whether encoded on the RHS or LHS).
             Note the differences of JNT Mail as described in
             Appendix B.

        -    Backwards compatibility with RFC 987/1026.

        -    To ensure that gateways generate consistent addresses.
             This is both to help end users, and to generate
             identical message ids.

        Further, it is recommended that all other attributes are
        generated according to this ordering, so that all attributes
        so encoded follow a consistent hierarchy.

        There will be some cases where an X.400 O/R address of this
        encoding will be generated by an end user from external
        information.  The ordering of attributes may be inverted or
        mixed.  For this reason, the following heuristics may be
        applied:

        -    If there is an Organisation attribute to the left of
             any Org Unit attribute, assume that the hierarchy is
             inverted.

        -    If an inversion of the Org Unit hierarchy generates a
             valid address, when the preferred order does not,
             assume that the hierarchy is inverted.

   2.   For the Organisational Units (OU) in MTS.ORAddress, the
        first OU in the SEQUENCE is the most significant, as
        specified in X.400.

   3.   For the Domain Defined Attributes in MTS.ORAddress, the



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        First Domain Defined Attribute in the SEQUENCE is the most
        significant.

        Note that although this ordering is mandatory for this
        mapping, there are NO implications on ordering significance
        within X.400, where this is a Management Domain issue.

4.3.4.  RFC 822 -> X.400

   There are two basic cases:

      1.   X.400 addresses encoded in RFC 822.  This will also include
           RFC 822 addresses which are given reversible encodings.

      2.   "Genuine" RFC 822 addresses.

   The mapping should proceed as follows, by first assuming case 1).

   STAGE I.

   1.   If the 822-address is not of the form:

                local-part "@" domain

        Go to stage II.

   NOTE:It may be appropriate to reduce a source route address
        to this form by removal of all bar the last domain.  In
        terms of the design intentions of RFC 822, this would
        be an incorrect action.  However, in most real cases,
        it will do the "right" thing and provide a better
        service to the end user.  This is a reflection on the
        excessive and inappropriate use of source routing in
        RFC 822 based systems.  Either approach, or the
        intermediate approach of stripping only domain
        references which reference the local gateway are
        conformant to this specification.

   2.   Attempt to parse EBNF.domain as:

                *( domain-syntax "." ) known-domain

        Where EBNF.known-domain is the longest possible match in a
        list of supported mappings (see Appendix F).  If this fails,
        and the EBNF.domain does not explicitly identify the local
        gateway, go to stage II.  If it succeeds, allocate the
        attributes associated with EBNF.known-domain, and
        systematically allocate the attributes implied by each



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        EBNF.domain-syntax component.  If the domain explicitly
        identifies the gateway, allocate no attributes.

   3.   If the local-part contains any characters not in
        PrintableString, go to stage II.

   4.   If the 822.local-part uses the 822.quoted-string encoding,
        remove this quoting.  Parse the (unquoted) 822.local-part
        according to the EBNF EBNF.std-or-address.  If this parse
        fails, parse the local-part according to the EBNF
        EBNF.encoded-pn.  The result is a set of type/value pairs.
        If the values generated conflict with those derived in step
        2 (e.g., a duplicated country attribute), the domain should
        be assumed to be an RFC 987 gateway.  In this case, take
        only the LHS derived attributes.  Otherwise add LHS and RHS
        derived attributes together.

   5.   Associate the EBNF.attribute-value syntax (determined from
        the identified type) with each value, and check that it
        conforms.  If not, go to stage II.

   6.   Ensure that the set of attributes conforms both to the
        MTS.ORAddress specification and to the restrictions on this
        set given in X.400.  If not go to stage II.

   7.   Build the O/R Address from this information.


   STAGE II.

   This will only be reached if the RFC 822 EBNF.822-address is not
   a valid X.400 encoding.  If the address is an 822-MTS recipient
   address, it must be rejected, as there is a need to interpret
   such an address in X.400.  For the 822-MTS return address, and
   any addresses in the RFC 822 header, they should now be encoded
   as RFC 822 addresses in an X.400 O/R Name:

   1.   Convert the EBNF.822-address to PrintableString, as
        specified in Chapter 3.

   2.   The "RFC-822" domain defined attribute should be generated
        from this string.

   3.   Build the rest of the O/R Address in the local Management
        Domain agreed manner, so that the O/R Address will receive a
        correct global interpretation.

   Note that the domain defined attribute value has a maximum length



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   of MTS.ub-domain-defined-attribute-value-length (128).  If this
   is exceeded by a mapping at the MTS level, then the gateway
   should reject the message in question.  If this occurs at the
   IPMS level, then the action should depend on the policy being
   taken, which is discussed in Section 5.1.3.

4.3.5.  X.400 -> RFC 822

   There are two basic cases:

   1.   RFC 822 addresses encoded in X.400.

   2.   "Genuine" X.400 addresses.  This may include symmetrically
        encoded RFC 822 addresses.

   When a MTS Recipient O/R Address is interpreted, gatewaying will be
   selected if there a single "RFC-822" domain defined attribute
   present.  In this case, use mapping A.  For other O/R Addresses
   which:

   1.   Contain the special attribute.

        AND

   2.   Identifies the local gateway or any other known gateway with
        the other attributes.

   Use mapping A.  In other cases, use mapping B.

   NOTE:
        A pragmatic approach would be to assume that any O/R
        Address with the special domain defined attribute identifies
        an RFC 822 address.  This will usually work correctly, but is
        in principle not correct.

   Mapping A

   1.   Map the domain defined attribute value to ASCII, as defined
        in Chapter 3.

   Mapping B

   This will be used for X.400 addresses which do not use the explicit
   RFC 822 encoding.

   1.   For all string encoded attributes, remove any leading or
        trailing spaces, and replace adjacent spaces with a single
        space.



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   2.   Noting the hierarchy specified in 4.3.1, determine the
        maximum set of attributes which have an associated domain
        specification.  If no match is found, allocate the domain as
        the domain specification of the local gateway, and go to
        step 4.

   3.   Following the 4.3.1 hierarchy and noting any omitted
        components implied by the mapping tables (see Appendix F),
        if each successive component exists, and conforms to the
        syntax EBNF.domain-syntax (as defined in 4.3.1), allocate
        the next subdomain.  At least one attribute of the X.400
        address should not be mapped onto subdomain, as
        822.local-part cannot be null.

   4.   If the remaining components are personal-name components,
        conforming to the restrictions of 4.2.1, then EBNF.encoded-
        pn should be derived to form 822.local-part.  In other cases
        the remaining components should simply be encoded as a
        822.local-part using the EBNF.std-or-address syntax.  If
        necessary, the 822.quoted-string encoding should be used.

        If the derived 822.local-part can only be encoded by use of
        822.quoted-string, then use of the mapping defined
        in [Kille89b] may be appropriate.  Use of this mapping is
        discouraged.

4.4.  Repeated Mappings

   The mappings defined are symmetrical and reversible across a single
   gateway.  The symmetry is particularly useful in cases of (mail
   exploder type) distribution list expansion.  For example, an X.400
   user sends to a list on an RFC 822 system which he belongs to.  The
   received message will have the originator and any 3rd party X.400 O/R
   Addresses in correct format (rather than doubly encoded).  In cases
   (X.400 or RFC 822) where there is common agreement on gateway
   identification, then this will apply to multiple gateways.

   When a message traverses multiple gateways, the mapping will always
   be reversible, in that a reply can be generated which will correctly
   reverse the path.  In many cases, the mapping will also be
   symmetrical, which will appear clean to the end user.  For example,
   if countries "AB" and "XY" have RFC 822 networks, but are
   interconnected by X.400, the following may happen:  The originator
   specifies:


           Joe.Soap@Widget.PTT.XY




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   This is routed to a gateway, which generates:

                C               = "XY"
                ADMD            = "PTT"
                PRMD            = "Griddle MHS Providers"
                Organisation    = "Widget Corporation"
                Surname         = "Soap"
                Given Name      = "Joe"

   This is then routed to another gateway where the mapping is reversed
   to give:

                Joe.Soap@Widget.PTT.XY

   Here, use of the gateway is transparent.

   Mappings will only be symmetrical where mapping tables are defined.
   In other cases, the reversibility is more important, due to the (far
   too frequent) cases where RFC 822 and X.400 services are partitioned.

   The syntax may be used to source route.  THIS IS STRONGLY
   DISCOURAGED.  For example:

      X.400 -> RFC 822  -> X.400

      C             = "UK"
      ADMD          = "Gold 400"
      PRMD          = "UK.AC"
      "RFC-822"     = "/PN=Duval/DD.Title=Manager/(a)Inria.ATLAS.FR"

   This will be sent to an arbitrary UK Academic Community gateway by
   X.400.  Then it will be sent by JNT Mail to another gateway
   determined by the domain Inria.ATLAS.FR (FR.ATLAS.Inria).  This will
   then derive the X.400 O/R Address:

      C             = "FR"
      ADMD          = "ATLAS"
      PRMD          = "Inria"
      PN.S          = "Duval"
      "Title"       = "Manager"

   Similarly:
   RFC 822 -> X.400 -> RFC 822

   "/C=UK/ADMD=BT/PRMD=AC/RFC-822=jj(a)seismo.css.gov/"
                                                  @monet.berkeley.edu

   This will be sent to monet.berkeley.edu by RFC 822, then to the AC



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   PRMD by X.400, and then to jj@seismo.css.gov by RFC 822.

4.5.  Directory Names

   Directory Names are an optional part of O/R Name, along with O/R
   Address.  The RFC 822 addresses are mapped onto the O/R Address
   component.  As there is no functional mapping for the Directory Name
   on the RFC 822 side, a textual mapping should be used.  There is no
   requirement for reversibility in terms of the goals of this
   specification.  There may be some loss of functionality in terms of
   third party recipients where only a directory name is given, but this
   seems preferable to the significant extra complexity of adding a full
   mapping for Directory Names.

4.6.  MTS Mappings

   The basic mappings at the MTS level are:

      1) 822-MTS originator ->
                    MTS.PerMessageSubmissionFields.originator-name
         MTS.OtherMessageDeliveryFields.originator-name ->
                    822-MTS originator

      2) 822-MTS recipient ->
                    MTS.PerRecipientMessageSubmissionFields
      MTS.OtherMessageDeliveryFields.this-recipient-name ->
                    822-MTS recipient

   822-MTS recipients and return addresses are encoded as EBNF.822-
   address.

   The MTS Originator is always encoded as MTS.OriginatorName, which
   maps onto MTS.ORAddressAndOptionalDirectoryName, which in turn maps
   onto MTS.ORName.

4.6.1.  RFC 822 -> X.400

   From the 822-MTS Originator, use the basic ORAddress mapping, to
   generate MTS.PerMessageSubmissionFields.originator-name (MTS.ORName),
   without a DirectoryName.

   For recipients, the following settings should be made for each
   component of MTS.PerRecipientMessageSubmissionFields.

        recipient-name
             This should be derived from the 822-MTS recipient by the
             basic ORAddress mapping.




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        originator-report-request
             This should be set according to content return policy, as
             discussed in Section 5.2.

        explicit-conversion
             This optional component should be omitted, as this service
             is not needed.

        extensions
             The default value (no extensions) should be used.

4.6.2.  X.400 -> RFC 822

   The basic functionality is to generate the 822-MTS originator and
   recipients.  There is information present on the X.400 side, which
   cannot be mapped into analogous 822-MTS services.  For this reason,
   new RFC 822 fields are added for the MTS Originator and Recipients.
   The information discarded at the 822-MTS level should be present in
   these fields.  There may also be the need to generate a delivery
   report.

4.6.2.1.  822-MTS Mappings

   Use the basic ORAddress mapping, to generate the 822-MTS originator
   (return address) from MTS.OtherMessageDeliveryFields.originator-name
   (MTS.ORName).  If MTS.ORName.directory-name is present, it should be
   discarded.

   The 822-MTS recipient is conceptually generated from
   MTS.OtherMessageDeliveryFields.this-recipient-name.  This is done by
   taking MTS.OtherMessageDeliveryFields.this-recipient-name, and
   generating an 822-MTS recipient according to the basic ORAddress
   mapping, discarding MTS.ORName.directory-name if present.  However,
   if this model was followed exactly, there would be no possibility to
   have multiple 822-MTS recipients on a single message.  This is
   unacceptable, and so layering is violated.  The mapping needs to use
   the MTA level information, and map each value of
   MTA.PerRecipientMessageTransferFields.recipient-name, where the
   responsibility bit is set, onto an 822-MTS recipient.

4.6.2.2.  Generation of RFC 822 Headers

   Not all per-recipient information can be passed at the 822-MTS level.
   For this reason, two new RFC 822 headers are created, in order to
   carry this information to the RFC 822 recipient.  These fields are
   "X400-Originator:"  and "X400-Recipients:".

   The "X400-Originator:" field should be set to the same value as the



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   822-MTS originator.  In addition, if
   MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName) contains
   MTS.ORName.directory-name then this Directory Name should be
   represented in an 822.comment.

   Recipient names, taken from each value of
   MTS.OtherMessageDeliveryFields.this-recipient-name and
   MTS.OtherMessageDeliveryFields.other-recipient-names should  be made
   available to the RFC 822 user by use of the "X400-Recipients:" field.
   By taking the recipients at the MTS level, disclosure of recipients
   will be dealt with correctly.  If any MTS.ORName.directory-name is
   present, it should be represented in an 822.comment.  If
   MTS.OtherMessageDeliveryFields.orignally-intended-recipient-name is
   present, then it should be represented in an associated 822.comment,
   starting with the string "Originally Intended Recipient".

   In addition, the following per-recipient services from
   MTS.OtherMessageDeliveryFields.extensions should be represented in
   comments if they are used.  None of these services can be provided on
   RFC 822 networks, and so in general these will be informative strings
   associated with other MTS recipients. In some cases, string values
   are defined.  For the remainder, the string value may be chosen by
   the implementor.   If the parameter has a default value, then no
   comment should be inserted.

        requested-delivery-method

        physical-forwarding-prohibited
             "(Physical Forwarding Prohibited)".

        physical-forwarding-address-request
             "(Physical Forwarding Address Requested)".

        physical-delivery-modes

        registered-mail-type

        recipient-number-for-advice

        physical-rendition-attributes

        physical-delivery-report-request
             "(Physical Delivery Report Requested)".

        proof-of-delivery-request
             "(Proof of Delivery Requested)".





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4.6.2.3.  Delivery Report Generation

   If MTA.PerRecipientMessageTransferFields.per-recipient-indicators
   requires a positive delivery notification, this should be
   generated by the gateway.  Supplementary Information should be
   set to indicate that the report is gateway generated.

4.6.3.  Message IDs (MTS)

   A mapping from 822.msg-id to MTS.MTSIdentifier is defined.  The
   reverse mapping is not needed, as MTS.MTSIdentifier is always
   mapped onto new RFC 822 fields.  The value of
   MTS.MTSIdentifier.local-part will facilitate correlation of
   gateway errors.

   To map from 822.msg-id, apply the standard mapping to
   822.msg-id, in order to generate an MTS.ORAddress.  The Country,
   ADMD, and PRMD components of this should be used to generate
   MTS.MTSIdentifier.global-domain-identifier.
   MTS.MTSIdentifier.local-identifier should be set to the
   822.msg-id, including the braces "<" and ">".  If this string is
   longer than MTS.ub-local-id-length (32), then it should be
   truncated to this length.

   The reverse mapping is not used in this specification.  It
   would be applicable where MTS.MTSIdentifier.local-identifier is
   of syntax 822.msg-id, and it algorithmically identifies
   MTS.MTSIdentifier.

4.7.  IPMS Mappings

   All RFC 822 addresses are assumed to use the 822.mailbox syntax.
   This should include all 822.comments associated with the lexical
   tokens of the 822.mailbox.  In the IPMS O/R Names are encoded as
   MTS.ORName.  This is used within the  IPMS.ORDescriptor,
   IPMS.RecipientSpecifier, and IPMS.IPMIdentifier.  An asymmetrical
   mapping is defined between these components.

4.7.1.  RFC 822 -> X.400

   To derive IPMS.ORDescriptor from an RFC 822 address.

      1.   Take the address, and extract an EBNF.822-address.  This can
           be derived trivially from either the 822.addr-spec or
           822.route-addr syntax.  This is mapped to MTS.ORName as
           described above, and used as IMPS.ORDescriptor.formal-name.

      2.   A string should be built consisting of (if present):



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           - The 822.phrase component if the 822.address is an
             822.phrase 822.route-addr construct.

           - Any 822.comments, in order, retaining the parentheses.

      This string should then be encoded into T.61 us a human
      oriented mapping (as described in Chapter 3).  If the string
      is not null, it should be assigned to
      IPMS.ORDescriptor.free-form-name.

      3.   IPMS.ORDescriptor.telephone-number should be omitted.

   If IPMS.ORDescriptor is being used in IPMS.RecipientSpecifier,
   IPMS.RecipientSpecifier.reply-request and
   IPMS.RecipientSpecifier.notification-requests should be set to
   default values (none and false).

   If the 822.group construct is present, any included 822.mailbox
   should be encoded as above to generate a separate IPMS.ORDescriptor.
   The 822.group should be mapped to T.61, and a IPMS.ORDescriptor with
   only an free-form-name component built from it.

4.7.2.  X.400 -> RFC 822

   Mapping from IPMS.ORDescriptor to RFC 822 address.  In the basic
   case, where IPMS.ORDescriptor.formal-name is present, proceed as
   follows.

      1.   Encode IPMS.ORDescriptor.formal-name (MTS.ORName) as
           EBNF.822-address.

      2a.  If IPMS.ORDescriptor.free-form-name is present, convert it
           to ASCII (Chapter 3), and use this as the 822.phrase
           component of 822.mailbox using the 822.phrase 822.route-addr
           construct.

      2b.  If IPMS.ORDescriptor.free-form-name is absent.  If
           EBNF.822-address is parsed as 822.addr-spec use this as the
           encoding of 822.mailbox.  If EBNF.822-address is parsed as
           822.route 822.addr-spec, then a 822.phrase taken from
           822.local-part should be added.

      3.   If IPMS.ORDescriptor.telephone-number is present, this
           should be placed in an 822.comment, with the string "Tel ".
           The normal international form of number should be used.  For
           example:

                  (Tel +44-1-387-7050)



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      4.   If IPMS.ORDescriptor.formal-name.directory-name is present,
           then a text representation should be placed in a trailing
           822.comment.

      5.   If IPMS.RecipientSpecifier.report-request has any non-
           default values, then an 822.comment "(Receipt Notification
           Requested)", and/or "(Non Receipt Notification Requested)",
           and/or "(IPM Return Requested)" should be appended to the
           address.  The effort of correlating P1 and P2 information is
           too great to justify the gateway sending Receipt
           Notifications.

      6.   If IPMS.RecipientSpecifier.reply-request is True, an
           822.comment "(Reply requested)" should be appended to the
           address.

   If IPMS.ORDescriptor.formal-name is absent, IPMS.ORDescriptor.free-
   form-name should be converted to ASCII, and used as 822.phrase within
   the RFC 822 822.group syntax.  For example:

      Free Form Name ":" ";"

   Steps 3-6 should then be followed.

4.7.3.  IP Message IDs

   There is a need to map both ways between 822.msg-id and
   IPMS.IPMIdentifier.  This allows for X.400 Receipt Notifications,
   Replies, and Cross References to reference an RFC 822 Message ID,
   which is preferable to a gateway generated ID.  A reversible and
   symmetrical mapping is defined.  This allows for good things to
   happen when messages pass multiple times across the X.400/RFC 822
   boundary.

   An important issue with messages identifiers is mapping to the exact
   form, as many systems use these ids as uninterpreted keys.  The use
   of table driven mappings is not always symmetrical, particularly in
   the light of alternative domain names, and alternative management
   domains.  For this reason, a purely algorithmic mapping is used.  A
   mapping which is simpler than that for addresses can be used for two
   reasons:

        -    There is no major requirement to make message IDs "natural"

        -    There is no issue about being able to reply to message IDs.
             (For addresses, creating a return path which works is more
             important than being symmetrical).




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   The mapping works by defining a way in which message IDs generated on
   one side of the gateway can be represented on the other side in a
   systematic manner.  The mapping is defined so that the possibility of
   clashes is is low enough to be treated as impossible.

4.7.3.1.  822.msg-id represented in X.400

   IPMS.IPMIdentifier.user is omitted.  The IPMS.IPMIdentifier.user-
   relative-identifier is set to a printable string encoding of the
   822.msg-id with the angle braces ("<" and ">") removed.

4.7.3.2.  IPMS.IPMIdentifier represented in RFC 822

   The 822.domain of 822.msg-id is set to the value "MHS".  The
   822.local-part of 822.msg-id is built as:

                [ printablestring ] "*"  [ std-or-address ]

   with EBNF.printablestring being the IPMS.IPMIdentifier.user-
   relative-identifier, and std-or-address being an encoding of the
   IPMS.IPMIdentifier.user.  If necessary, the 822.quoted-string
   encoding is used.  For example:

        <"147*/S=Dietrich/O=Siemens/ADMD=DBP/C=DE/"@MHS>

4.7.3.3.  822.msg-id -> IPMS.IPMIdentifier

   If the 822.local-part can be parsed as:

                [ printablestring ] "*"  [ std-or-address ]

   and the 822.domain is "MHS", then this ID was X.400 generated.  If
   EBNF.printablestring is present, the value is assigned to
   IPMS.IPMIdentifier.user-relative-identifier.  If EBNF.std-or-address
   is present, the O/R Address components derived from it are used to
   set IPMS.IPMIdentifier.user.

   Otherwise, this is an RFC 822 generated ID.  In this case, set
   IPMS.IPMIdentifier.user-relative-identifier to a printable string
   encoding of the 822.msg-id without the angle braces.

4.7.3.4.  IPMS.IPMIdentifier -> 822.msg-id

   If IPMS.IPMIdentifier.user is absent, and IPMS.IPMIdentifier.user-
   relative-identifier mapped to ASCII and angle braces added parses as
   822.msg-id, then this is an RFC 822 generated ID.

   Otherwise, the ID is X.400 generated.  Use the



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   IPMS.IPMIdentifier.user to generate an EBNF.std-or-address form
   string.  Build the 822.local-part of the 822.msg-id with the syntax:

                [ printablestring ] "*"  [ std-or-address ]

   The printablestring is taken from IPMS.IPMIdentifier.user-relative-
   identifier.  Use 822.quoted-string if necessary.  The 822.msg-id is
   generated with this 822.local-part, and "MHS" as the 822.domain.

4.7.3.5.  Phrase form

   In "Reply-To:" and "References:", the encoding 822.phrase may be used
   as an alternative to 822.msg-id.  To map from 822.phrase to
   IPMS.IPMIdentifier, assign IPMS.IPMIdentifier.user-relative-
   identifier to the phrase.  When mapping from IPMS.IPMIdentifier for
   "Reply-To:" and "References:", if IPMS.IPMIdentifier.user is absent
   and IPMS.IPMIdentifier.user-relative-identifier does not parse as
   822.msg-id, generate an 822.phrase rather than adding the domain MHS.

4.7.3.6.  RFC 987 backwards compatibility

   The mapping proposed here is different to that used in RFC 987, as
   the RFC 987 mapping lead to changed message IDs in many cases.
   Fixing the problems is preferable to retaining backwards
   compatibility.  An implementation of this standard is encouraged to
   recognise message IDs generated by RFC 987.

Chapter 5 -- Detailed Mappings

   This chapter gives detailed mappings for the functions outlined in
   Chapters 1 and 2.  It makes extensive use of the notations and
   mappings defined in Chapters 3 and 4.

5.1.  RFC 822 -> X.400

5.1.1.  Basic Approach

   A single IP Message is generated.  The RFC 822 headers are used to
   generate the IPMS.Heading.  The IP Message will have one IA5
   IPMS.BodyPart containing the RFC 822 message body.

   Some RFC 822 fields cannot be mapped onto a standard IPM Heading
   field, and so an extended field is defined in Section 5.1.2.  This is
   then used for fields which cannot be mapped onto existing services.

   The message is submitted to the MTS, and the services required can be
   defined by specifying MTS.MessageSubmissionEnvelope.  A few
   parameters of the MTA Abstract service are also specified, which are



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   not in principle available to the MTS User.  Use of these services
   allows RFC 822 MTA level parameters to be carried in the analogous
   X.400 service elements.  The advantages of this mapping far outweigh
   the layering violation.

5.1.2.  X.400 Extension Field

   An IPMS Extension is defined:

                rfc-822-field HEADING-EXTENSION
                        VALUE RFC822Field
                        ::= id-rfc-822-field

                RFC822Field ::= IA5String

   The Object Identifier id-rfc-822-field is defined in Appendix D.

   To encode any RFC 822 Header using this extension, the RFC822Field
   should be set to the  822.field omitting the trailing CRLF (e.g.,
   "Fruit-Of-The-Day: Kiwi Fruit"). Structured fields should be
   unfolded.  There should be no space before the ":".  The reverse
   mapping builds the RFC 822 field in a straightforward manner.

5.1.3.  Generating the IPM

   The IPM (IPMS Service Request) is generated according to the rules of
   this section.  The IPMS.IPM.body usually consists of one
   IPMS.BodyPart of type IPMS.IA5TextbodyPart with
   IPMS.IA5TextBodyPart.parameters.repertoire set to the default (ia5)
   which contains the body of the RFC 822 message.  The exception is
   where there is a "Comments:" field in the RFC 822 header.

   If no specific 1988 features are used, the IPM generated should be
   encoded as content type 2.  Otherwise, it should be encoded as
   content type 22.  The latter will always be the case if extension
   heading fields are generated.

   When generating the IPM, the issue of upper bounds must be
   considered.  At the MTS and MTA level, this specification is strict
   about enforcing upper bounds.  Three options are available at the IPM
   level.  Use of any of these options conforms to this standard.

      1.   Ignore upper bounds, and generate messages in the natural
           manner.  This assumes that if any truncation is done, it
           will happen at the recipient UA.  This will maximise
           transfer of information, but may break some recipient UAs.

      2.   Reject any inbound message which would cause a message



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           violating constraints to be generated.  This will be robust,
           but may prevent useful communication.

      3.   Truncate fields to the upper bounds specified in X.400.
           This will prevent problems with UAs which enforce upper
           bounds, but will sometimes discard useful information.

   These choices have different advantages and disadvantages, and the
   choice will depend on the exact application of the gateway.

   The rest of this section concerns IPMS.IPM.heading (IPMS.Heading).
   The only mandatory component of IPMS.Heading is the
   IPMS.Heading.this-IPM (IPMS.IPMIdentifier).  A default should be
   generated by the gateway.  With the exception of "Received:", the
   values of multiple fields should be merged (e.g., If there are two
   "To:" fields, then the mailboxes of both should be used).
   Information should be generated from the standard RFC 822 Headers as
   follows:

        Date:
             Ignore (Handled at MTS level)

        Received:
             Ignore (Handled at MTA level)

        Message-Id:
             Mapped to IPMS.Heading.this-IPM.  For these, and all other
             fields containing 822.msg-id the mappings of Chapter 4 are
             used for each 822.msg-id.

        From:
             If Sender: is present, this is mapped to
             IPMS.Heading.authorizing-users.  If not, it is mapped to
             IPMS.Heading.originator.  For this, and other components
             containing addresses, the mappings of Chapter 4 are used
             for each address.

        Sender:
             Mapped to IPMS.Heading.originator.

        Reply-To:
             Mapped to IPMS.Heading.reply-recipients.

        To:  Mapped to IPMS.Heading.primary-recipients

        Cc:  Mapped to IPMS.Heading.copy-recipients.

        Bcc: Mapped to IPMS.Heading.blind-copy-recipients.



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        In-Reply-To:
             If there is one value, it is mapped to
             IPMS.Heading.replied-to-IPM, using the 822.phrase or
             822.msg-id mapping as appropriate.  If there are several
             values, they are mapped to IPMS.Heading.related-IPMs, along
             with any values from a "References:" field.

        References:
             Mapped to IPMS.Heading.related-IPMs.

        Keywords:
             Mapped onto a heading extension.

        Subject:
             Mapped to IPMS.Heading.subject.  The field-body uses the
             human oriented mapping referenced in Chapter 3 from ASCII to
             T.61.

        Comments:
             Generate an IPMS.BodyPart of type IPMS.IA5TextbodyPart with
             IPMS.IA5TextBodyPart.parameters.repertoire set to the
             default (ia5), containing the value of the fields, preceded
             by the string "Comments: ".  This body part should precede
             the other one.

        Encrypted:
             Mapped onto a heading extension.

        Resent-*
             Mapped onto a heading extension.

             Note that it would be possible to use a ForwardedIPMessage
             for these fields, but the semantics are (arguably) slightly
             different, and it is probably not worth the effort.

        Other Fields
             In particular X-* fields, and "illegal" fields in common
             usage (e.g., "Fruit-of-the-day:") are mapped onto a heading
             extension, unless covered by another section or appendix of
             this specification.  The same treatment should be applied to
             RFC 822 fields where the content of the field does not
             conform to RFC 822 (e.g., a Date: field with unparsable
             syntax).

5.1.4.  Mappings to the MTS Abstract Service

   The MTS.MessageSubmissionEnvelope comprises
   MTS.PerMessageSubmissionFields, and



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   MTS.PerRecipientMessageSubmissionFields.  The mandatory parameters
   should be defaulted as follows.

        MTS.PerMessageSubmissionFields.originator-name
             This is always generated from 822-MTS, as defined in
             Chapter 4.

        MTS.PerMessageSubmissionFields.content-type
             Set to the value implied by the encoding of the IPM (2 or
             22).

        MTS.PerRecipientMessageSubmissionFields.recipient-name
             These will always be supplied from 822-MTS, as defined in
             Chapter 4.

   Optional components should be left out, and default components
   defaulted, with two exceptions.  For
   MTS.PerMessageSubmissionFields.per-message-indicators, the following
   settings should be made:

   -    Alternate recipient should be allowed, as it seems desirable
        to maximise the opportunity for (reliable) delivery.

   -    Content return request should be set according to the issues
        discussed in Section 5.2.

   MTS.PerMessageSubmissionFields.original-encoded-information-types
   should be made a set of one element
   BuiltInEncodedInformationTypes.ia5-text.

   The MTS.PerMessageSubmissionFields.content-correlator should be
   encoded as IA5String, and contain the Subject:, Message-ID:, Date:,
   and To: fields (if present).  This should include the strings
   "Subject:", "Date:", "To:", "Message-ID:", and appropriate folding.
   This should be truncated to MTS.ub-content-correlator-length (512)
   characters.  In addition, if there is a "Subject:" field, the
   MTS.PerMessageSubmissionFields.content-identifier, should be set to a
   printable string representation of the contents of it, truncated to
   MTS.ub-content-id-length (16).  Both are used, due to the much larger
   upper bound of the content correlator, and that the content id is
   available in X.400(1984).

5.1.5.  Mappings to the MTA Abstract Service

   There is a need to map directly onto some aspects of the MTA Abstract
   service, for the following reasons:

   -    So the the MTS Message Identifier can be generated from the



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        RFC 822 Message-ID:.

   -    So that the submission date can be generated from the
        822.Date.

   -    To prevent loss of trace information.

   -    To prevent RFC 822/X.400 looping caused by distribution
        lists or redirects.

   The following mappings are defined.

   Message-Id:
        If this is present, the
        MTA.PerMessageTransferFields.message-identifier should be
        generated from it, using the mappings described in
        Chapter 4.

   Date:
        This is used to set the first component of
        MTA.PerMessageTransferFields.trace-information
        (MTA.TraceInformationElement).  The 822-MTS originator
        should be mapped into an MTS.ORAddress, and used to derive
        MTA.TraceInformationElement.global-domain-identifier.  The
        optional components of
        MTA.TraceInformationElement.domain-supplied-information are
        omitted, and the mandatory components are set as follows:

          MTA.DomainSuppliedInformation.arrival-time
             This is set to the date derived from Date:

          MTA.DomainSuppliedInformation.routing-action
             Set to relayed.

        The first element of
        MTA.PerMessageTransferFields.internal-trace-information
        should be generated in an analogous manner, although this
        may later be dropped (see the procedures for "Received:").

   Received:
        All RFC 822 trace is used to derive
        MTA.PerMessageTransferFields.trace-information and
        MTA.PerMessageTransferFields.internal-trace-information.
        Processing of Received: lines should follow processing of
        Date:, and should be done from the the bottom to the top of
        the RFC 822 header (i.e., in chronological order).  If other
        trace elements are processed (Via:, X400-Received:), care
        should be taken to keep the relative ordering correct.  The



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        initial element of
        MTA.PerMessageTransferFields.trace-information will be
        generated already (from Date:).

        Consider the Received: field in question.  If the "by"  part
        of the received is present, use it to derive an
        MTS.GlobalDomainIdentifier.  If this is different from the
        one in the last element of
        MTA.PerMessageTransferFields.trace-information
        (MTA.TraceInformationElement.global-domain-identifier)
        create a new MTA.TraceInformationElement, and optionally
        remove
        MTA.PerMessageTransferFields.internal-trace-information.
        This removal should be done in cases where the message is
        being transferred to another MD where there is no bilateral
        agreement to preserve internal trace beyond the local MD.
        The trace creation is as for internal trace described below,
        except that no MTA field is needed.

        Then add a new element (MTA.InternalTraceInformationElement)
        to MTA.PerMessageTransferFields.internal-trace-information,
        creating this if needed.  This shall be done, even if
        inter-MD trace is created.  The
        MTA.InternalTraceInformationElement.global-domain-identifier
        should be set to the value derived.  The
        MTA.InternalTraceInformationElement.mta-supplied-information
        (MTA.MTASuppliedInformation) should be set as follows:

          MTA.MTASuppliedInformation.arrival-time
             Derived from the date of the Received: line

          MTA.MTASuppliedInformation.routing-action
             Set to relayed

        The MTA.InternalTraceInformationElement.mta-name should be
        taken from the "by" component of the "Received:" field,
        truncated to MTS.ub-mta-name-length (32).  For example:

           Received: from computer-science.nottingham.ac.uk by
              vs6.Cs.Ucl.AC.UK via Janet with NIFTP  id aa03794;
              28 Mar 89 16:38 GMT

   Generates the string:

           vs6.Cs.Ucl.AC.UK

   Note that before transferring the message to some ADMDs, additional
   trace stripping may be required, as the implied path through multiple



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   MDs would violate ADMD policy.

   Two extended fields must be mapped, in order to prevent looping.
   "DL-Expansion-History:" is mapped to
   MTA.PerMessageTransferFields.extensions.dl-expansion-history.
   "Redirection-History:" is mapped to
   MTA.PerRecipientMessageTransferFields.extensions.redirection-history.

5.1.6.  Mapping New Fields

   This specification defines a number of new fields for Reports,
   Notifications and IP Messages in Section 5.3.  As this specification
   only aims to preserve existing services, a gateway conforming to this
   specification does not need to map these fields to X.400, with the
   exception of "DL-Expansion-History" and "Redirection-History"
   described in the previous section.  However, it is usually desirable
   and beneficial to do so, particularly to facilitate support of a
   message traversing multiple gateways.  These mappings may be onto
   MTA, MTS, or IPMS services.

5.2.  Return of Contents

   It is not clear how widely supported the X.400 return of contents
   service will be.  Experience with X.400(1984) suggests that support
   of this service may not be universal.  As this service is expected in
   the RFC 822 world, two approaches are specified.  The choice will
   depend on the use of X.400 return of contents withing the X.400
   community being serviced by the gateway.

   In environments where return of contents is widely supported, content
   return can be requested as a service.  The content return service can
   then be passed back to the end (RFC 822) user in a straightforward
   manner.

   In environments where return of contents is not widely supported, a
   gateway must make special provision to handle return of contents.
   For every message passing from RFC 822 -> X.400, content return
   request will not be requested, and report request always will be.
   When the delivery report comes back, the gateway can note that the
   message has been delivered to the recipient(s) in question.  If a
   non-delivery report is received, a meaningful report (containing some
   or all of the original message) can be sent to the 822-MTS
   originator.  If no report is received for a recipient, a (timeout)
   failure notice should be sent to the 822-MTS originator.  The gateway
   may retransmit the X.400 message if it wishes.  When this approach is
   taken, routing must be set up so that error reports are returned
   through the same MTA.  This approach may be difficult to use in
   conjunction with some routing strategies.



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5.3.  X.400 -> RFC 822

5.3.1.  Basic Approach

   A single RFC 822 message is generated from the incoming IP Message,
   Report, or IP Notification.   All IPMS.BodyParts are mapped onto a
   single RFC 822 body.  Other services are mapped onto RFC 822 header
   fields.  Where there is no appropriate existing field, new fields are
   defined for IPMS, MTS and MTA services.

   The gateway mechanisms will correspond to MTS Delivery.  As with
   submission, there are aspects where the MTA (transfer) services are
   also used. In particular, there is an optimisation to allow for
   multiple 822-MTS recipients.

5.3.2.  RFC 822 Settings

   An RFC 822 Service requires to have a number of mandatory fields in
   the RFC 822 Header.  Some 822-MTS services mandate specification of
   an 822-MTS Originator.  Even in cases where this is optional, it is
   usually desirable to specify a value.  The following defaults are
   defined, which should be used if the mappings specified do not derive
   a value:

   822-MTS Originator
        If this is not generated by the mapping (e.g., for a
        Delivery Report), a value pointing at a gateway
        administrator should be assigned.

   Date:
        A value will always be generated

   From:If this is not generated by the mapping, it should be
        assigned equal to the 822-MTS Originator.  If this is
        gateway generated, an appropriate 822.phrase should be
        added.

   At least one recipient field
        If no recipient fields are generated, a field "To: list:;",
        should be added.

   This will ensure minimal RFC 822 compliance.  When generating RFC
   822 headers, folding should be used in an appropriate manner.








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5.3.3.  Basic Mappings

5.3.3.1.  Encoded Information Types

   This mapping from MTS.EncodedInformationTypes is needed in
   several disconnected places.  EBNF is defined as follows:

                encoded-info    = 1#encoded-type

                encoded-type    = built-in-eit / object-identifier

                built-in-eit    = "Undefined"         ; undefined (0)
                                / "Telex"             ; tLX (1)
                                / "IA5-Text"          ; iA5Text (2)
                                / "G3-Fax"            ; g3Fax (3)
                                / "TIF0"              ; tIF0 (4)
                                / "Teletex"           ; tTX (5)
                                / "Videotex"          ; videotex (6)
                                / "Voice"             ; voice (7)
                                / "SFD"               ; sFD (8)
                                / "TIF1"              ; tIF1 (9)

   MTS.EncodedInformationTypes is mapped onto EBNF.encoded-info.
   MTS.EncodedInformationTypes.non-basic-parameters is ignored.  Built
   in types are mapped onto fixed strings (compatible with X.400(1984)
   and RFC 987), and other types are mapped onto EBNF.object-identifier.

5.3.3.2.  Global Domain Identifier

   The following simple EBNF is used to represent
   MTS.GlobalDomainIdentifier:

                global-id = std-or-address

   This is encoded using the std-or-address syntax, for the attributes
   within the Global Domain Identifier.

5.3.4.  Mappings from the IP Message

   Consider that an IPM has to be mapped to RFC 822.  The IPMS.IPM
   comprises an IPMS.IPM.heading and IPMS.IPM.body.   The heading is
   considered first.  Some EBNF for new fields is defined:

                ipms-field = "Obsoletes" ":" 1#msg-id
                           / "Expiry-Date" ":" date-time
                           / "Reply-By" ":" date-time
                           / "Importance" ":" importance
                           / "Sensitivity" ":" sensitivity



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                           / "Autoforwarded" ":" boolean
                           / "Incomplete-Copy" ":"
                           / "Language" ":" language
                           / "Message-Type" ":" message-type
                           / "Discarded-X400-IPMS-Extensions" ":" 1#oid



                importance      = "low" / "normal" / "high"


                sensitivity     = "Personal" / "Private" /
                                       "Company-Confidential"

                language        = 2*ALPHA [ language-description ]
                language-description = printable-string


                message-type    = "Delivery Report"
                                / "InterPersonal Notification"
                                / "Multiple Part"

   The mappings and actions for the IPMS.Heading is now specified for
   each element.  Addresses, and Message Identifiers are mapped
   according to Chapter 4.  Other mappings are explained, or are
   straightforward (algorithmic).

   IPMS.Heading.this-IPM
        Mapped to "Message-ID:".

   IPMS.Heading.originator
        If IPMS.Heading.authorizing-users is present this is mapped
        to Sender:, if not to "From:".

   IPMS.Heading.authorizing-users
        Mapped to "From:".

   IPMS.Heading.primary-recipients
        Mapped to "To:".

   IPMS.Heading.copy-recipients
        Mapped to "Cc:".

   IPMS.Heading.blind-copy-recipients
        Mapped to "Bcc:".

   IPMS.Heading.replied-to-ipm
        Mapped to "In-Reply-To:".



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   IPMS.Heading.obsoleted-IPMs
        Mapped to the extended RFC 822 field "Obsoletes:"

   IPMS.Heading.related-IPMs
        Mapped to "References:".

   IPMS.Heading.subject
        Mapped to "Subject:".  The contents are converted to ASCII
        (as defined in Chapter 3).  Any CRLF are not mapped, but
        are used as points at which the subject field must be
        folded.

   IPMS.Heading.expiry-time
        Mapped to the extended RFC 822 field "Expiry-Date:".

   IPMS.Heading.reply-time
        Mapped to the extended RFC 822 field "Reply-By:".

   IPMS.Heading.reply-recipients
        Mapped to "Reply-To:".

   IPMS.Heading.importance
        Mapped to the extended RFC 822 field "Importance:".

   IPMS.Heading.sensitivity
        Mapped to the extended RFC 822 field "Sensitivity:".

   IPMS.Heading.autoforwarded
        Mapped to the extended RFC 822 field "Autoforwarded:".

   The standard extensions (Annex H of X.420 / ISO 10021-7) are mapped
   as follows:

   incomplete-copy
        Mapped to the extended RFC 822 field "Incomplete-Copy:".

   language
        Mapped to the extended RFC 822 field "Language:", filling in
        the two letter code. If possible, the language-description
        should be filled in with a human readable description of the
        language.

   If the RFC 822 extended header is found, this should be mapped onto
   an RFC 822 header, as described in Section 5.1.2.

   If a non-standard extension is found, it should be discarded, unless
   the gateway understands the extension and can perform an appropriate
   mapping onto an RFC 822 header field.  If extensions are discarded,



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   the list should be indicated in the extended RFC 822 field
   "Discarded-X400-IPMS-Extensions:".

   The IPMS.Body is mapped into the RFC 822 message body.  Each
   IPMS.BodyPart is converted to ASCII as follows:

   IPMS.IA5Text
        The mapping is straightforward (see Chapter 3).

   IPMS.MessageBodyPart
        The X.400 -> RFC 822 mapping  should be recursively applied,
        to generate an RFC 822 Message.  If present, the
        IPMS.MessageBodyPart.parameters.delivery-envelope should be
        used for the MTS Abstract Service Mappings.  If present, the
        IPMS.MessageBodyPart.parameters.delivery-time should be
        mapped to the extended RFC 822 field "Delivery-Date:".

   Other
        If other body parts can be mapped to IA5, either by use of
        mappings defined in X.408 [CCITT88a], or by other reasonable
        mappings, this should be done unless content conversion is
        prohibited.

   If some or all of the body parts cannot be converted there are three
   options.  All of these conform to this standard.  A different choice
   may be made for the case where no body part can be converted:

   1.   The first option is to reject the message, and send a non-
        delivery notification.  This must always be done if
        conversion is prohibited.

   2.   The second option is to map a missing body part to something
        of the style:

                *********************************

                There was a foobar here

                The widget gateway ate it

                *********************************

        This will allow some useful information to be transferred.
        As the recipient is a human (IPMS), then suitable action
        should be available.

   3.   Finally both can be done.  In this case, the supplementary
        information in the (positive) Delivery Report should make



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        clear that something was sent on to the recipient with
        substantial loss of information.

   Where there is more than one IPMS.BodyPart, the mapping defined by
   Rose and Stefferud in [Rose85a], should be used to map the separate
   IPMS.BodyParts in the single RFC 822 message body.  If this is done,
   a "Message-Type:" field with value "Multiple part" should be added,
   which will indicate to a receiving gateway that the message may be
   unfolded according to RFC 934.

   For backwards compatibility with RFC 987, the following procedures
   should also be followed.  If there are two IA5 body parts, and the
   first starts with the string "RFC-822-Headers:" as the first line,
   then the remainder of this body part should be appended to the RFC
   822 header.

5.3.5.  Mappings from an IP Notification

   A message is generated, with the following fields:

   From:
        Set to the MTS.MessageDeliveryEnvelope.other-
        fields.originator-name.

   To:  Set to the IPMS.IPN.ipm-originator.

   Subject:
        Set to something of the form "X.400 Inter-Personal Receipt
        Notification".

   Message-Type:
        Set to "InterPersonal Notification"

   References:
        Set to IPMS.IPN.subject-ipm

   The following EBNF is defined for the body of the Message.  This
   format is defined to ensure that all information from an
   interpersonal notification is available to the end user in a uniform
   manner.

           ipn-body-format = ipn-description <CRLF>
                           [ ipn-extra-information <CRLF> ]
                           ipn-content-return

           ipn-description = ipn-receipt / ipn-non-receipt

           ipn-receipt = "Your message to:" preferred-recipient <CRLF>



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                    "was received at" receipt-time <CRLF> <CRLF>
                    "This notification was generated"
                    acknowledgement-mode <CRLF>
                    "The following extra information was given:" <CRLF>
                    ipn-suppl <CRLF>

           ipn-non-receipt "Your message to:"
                   preferred-recipient <CRLF>
                   ipn-reason


           ipn-reason = ipn-discarded / ipn-auto-forwarded

           ipn-discarded = "was discarded for the following reason:"
                           discard-reason <CRLF>

           ipn-auto-forwarded = "was automatically forwarded." <CRLF>
                           [ "The following comment was made:"
                                   auto-comment ]


           ipn-extra-information =
                    "The following information types were converted:"
                    encoded-info

           ipn-content-return = "The Original Message is not available"
                           / "The Original Message follows:"
                             <CRLF> <CRLF> message


           preferred-recipient = mailbox
           receipt-time        = date-time
           auto-comment        = printablestring
           ipn-suppl           = printablestring

           non-receipt-reason = "Discarded" / "Auto-Forwarded"

           discard-reason     = "Expired" / "Obsoleted" /
                                   "User Subscription Terminated"

           acknowledgement-mode = "Manually" / "Automatically"

   The mappings for elements of the common fields of IPMS.IPN
   (IPMS.CommonFields) onto this structure and the message header are:

        subject-ipm
             Mapped to "References:"




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        ipm-originator
             Mapped  to "To:".

        ipm-preferred-recipient
             Mapped to EBNF.preferred-recipient

        conversion-eits
             Mapped to EBNF.encoded-info in EBNF.ipn-extra-information

        The mappings for elements of IPMS.IPN.non-receipt-fields
        (IPMS.NonReceiptFields) are:

        non-receipt-reason
             Used to select between EBNF.ipn-discarded and
             EBNF.ipn-auto-forwarded

        discard-reason
             Mapped to EBNF.discard-reason

        auto-forward-comment
             Mapped to EBNF.auto-comment

        returned-ipm
             If present, the second option of EBNF.ipn-content-return
             should be chosen, and an RFC 822 mapping of the message
             included.  Otherwise the first option should be chosen.

        The mappings for elements of IPMS.IPN.receipt-fields
        (IPMS.ReceiptFields) are:

        receipt-time
             Mapped to EBNF.receipt-time

        acknowledgement-mode
             Mapped to EBNF.acknowledgement-mode

        suppl-receipt-info
             Mapped to EBNF.ipn-suppl

   An example notification is:

      From: Steve Kille <steve@cs.ucl.ac.uk>
      To: Julian Onions <jpo@computer-science.nottingham.ac.uk>
      Subject: X400 Inter-personal Receipt Notification
      Message-Type: InterPersonal Notification
      References: <1229.614418325@UK.AC.NOTT.CS>
      Date: Wed, 21 Jun 89 08:45:25 +0100




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      Your message to: Steve Kille <steve@cs.ucl.ac.uk>
      was automatically forwarded.
      The following comment was made:
      Sent on to a random destination

      The following information types were converted: g3fax

      The Original Message is not available

5.3.6.  Mappings from the MTS Abstract Service

   This section describes the MTS mappings for User Messages (IPM and
   IPN).  This mapping is defined by specifying the mapping of
   MTS.MessageDeliveryEnvelope.  The following extensions to RFC 822 are
   defined to support this mapping:

      mts-field = "X400-MTS-Identifier" ":" mts-msg-id
                / "X400-Originator" ":" mailbox
                / "X400-Recipients" ":" 1#mailbox
                / "Original-Encoded-Information-Types" ":"
                                encoded-info
                / "X400-Content-Type" ":" mts-content-type
                / "Content-Identifier" ":" printablestring
                / "Priority" ":" priority
                / "Originator-Return-Address" ":" 1#mailbox
                / "DL-Expansion-History" ":" mailbox ";" date-time ";"
                / "Redirection-History" ":" redirection
                / "Conversion" ":" prohibition
                / "Conversion-With-Loss" ":" prohibition
                / "Requested-Delivery-Method" ":"
                                1*( labelled-integer )
                / "Delivery-Date" ":" date-time
                / "Discarded-X400-MTS-Extensions" ":"
                                1#( oid / labelled-integer )


      prohibition     = "Prohibited" / "Allowed"

      mts-msg-id       = "[" global-id ";" *text "]"

      mts-content-type = "P2" /  labelled-integer
                      / object-identifer

      priority        = "normal" / "non-urgent" / "urgent"

      redirection     = mailbox ";" "reason" "="
                              redirection-reason
                              ";" date-time



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      redirection-reason =
                      "Recipient Assigned Alternate Recipient"
                    / "Originator Requested Alternate Recipient"
                    / "Recipient MD Assigned Alternate Recipient"

     The mappings for each element of MTS.MessageDeliveryEnvelope can
     now be considered.

     MTS.MessageDeliveryEnvelope.message-delivery-identifier
          Mapped to the extended RFC 822 field "X400-MTS-Identifier:".

     MTS.MessageDeliveryEnvelope.message-delivery-time
          Discarded, as this time will be represented in an
          appropriate trace element.

     The mappings for elements of
     MTS.MessageDeliveryEnvelope.other-fields
     (MTS.OtherMessageDeliveryFields) are:

     content-type
          Mapped to the extended RFC 822 field "X400-Content-Type:".
          The string "P2" is for backwards compatibility with RFC 987.
          If the content type is 22, then a labelled-integer encoding
          should be used.

     originator-name
          Mapped to the 822-MTS originator, and to the extended RFC
          822 field "X400-Originator:".  This is described in
          Section 4.6.2.

     original-encoded-information-types
          Mapped to the extended RFC 822 field
          "Original-Encoded-Information-Types:".

     priority
          Mapped to the extended RFC 822 field "Priority:".

     delivery-flags
          If the conversion-prohibited bit is set, add an extended RFC
          822 field "Conversion:".

     this-recipient-name and other-recipient-names
          These fields are used together, to generate the extended RFC
          822 field "X400-Recipients:".  Note that the latter will
          only be present if disclosure of recipients is allowed.

     originally-intended-recipient-name
          Mapped to a comment associated with the recipient in



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          question, as described in Section 4.6.2.2.

    converted-encoded-information-types
          Discarded, as it will always be IA5 only.

    message-submission-time
          Mapped to Date:.

    content-identifier
          Mapped to the extended RFC 822 field "Content-Identifier:".

    If any extensions
    (MTS.MessageDeliveryEnvelope.other-fields.extensions) are
    present, and they are marked as critical for transfer or
    delivery, then the message should be rejected.  The extensions
    (MTS.MessageDeliveryEnvelope.other-fields.extensions) are mapped
    as follows.

    conversion-with-loss-prohibited
          If set to
          MTS.ConversionWithLossProhibited.conversion-with-loss-prohibited,
          then add the extended RFC 822 field "Conversion-With-Loss:".

    requested-delivery-method
          Mapped to the extended RFC 822 field
          "Requested-Delivery-Method:".

    originator-return-address
          Mapped to the extended RFC 822 field
          "Originator-Return-Address:".

    physical-forwarding-address-request
    physical-delivery-modes
    registered-mail-type
    recipient-number-for-advice
    physical-rendition-attributes
    physical-delivery-report-request
    physical-forwarding-prohibited

      These elements are only appropriate for physical delivery.  They
      are represented as comments in the "X400-Recipients:" field, as
      described in Section 4.6.2.2.

    originator-certificate
    message-token
    content-confidentiality-algorithm-identifier
    content-integrity-check
    message-origin-authentication-check



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    message-security-label
    proof-of-delivery-request

      These elements imply use of security services not available in the
      RFC 822 environment.  If they are marked as critical for transfer
      or delivery, then the message should be rejected.  Otherwise they
      should be discarded.

    redirection-history
        Each element is mapped to an extended RFC 822 field
        "Redirection-History:".  They should be ordered in the
        message header, so that the most recent redirection comes
        first (same order as trace).

    dl-expansion-history
        Each element is mapped to the extended RFC 822 field
        "DL-Expansion-History:".  They should be ordered in the
        message header, so that the most recent expansion comes
        first (same order as trace).

   If any MTS (or MTA) Extensions not specified in X.400 are present,
   and they are marked as critical for transfer or delivery, then the
   message should be rejected.  If they are not so marked, they can
   safely be discarded.  The list of discarded fields should be
   indicated in the extended header "Discarded-X400-MTS-Extensions:".

5.3.7.  Mappings from the MTA Abstract Service

   There are some mappings at the MTA Abstract Service level which are
   done for IPM and IPN.  These can be derived from
   MTA.MessageTransferEnvelope.  The reasons for the mappings at this
   level, and the violation of layering are:

   -    Allowing for multiple recipients to share a single RFC 822
        message.

   -    Making the X.400 trace information available on the RFC 822
        side.

   -    Making any information on deferred delivery available.

   The 822-MTS recipients should be calculated from the full list of
   X.400 recipients.  This is all of the members of
   MTA.MessageTransferEnvelope.per-recipient-fields being passed
   through the gateway, where the responsibility bit is set.  In
   some cases, a different RFC 822 message would be calculated for
   each recipient.  If this is due to differing service requests for
   each recipient, then a different message should be generated.



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   If it is due only to the request for non-disclosure of
   recipients, then the "X400-Recipients:" field should be omitted,
   and only one message sent.

   The following EBNF is defined for extended RFC 822 headers:

      mta-field       = "X400-Received" ":" x400-trace
                      / "Deferred-Delivery" ":" date-time
                      / "Latest-Delivery-Time" ":" date-time


      x400-trace       = "by" md-and-mta ";"
                       [ "deferred until" date-time ";" ]
                       [ "converted" "(" encoded-info ")" ";" ]
                       [ "attempted" md-and-mta ";"  ]
                          action-list
                          ";" arrival-time


      md-and-mta       = [ "mta" mta "in" ]  global-id
      mta              = word
      arrival-time     = date-time


      action-list      = 1#action
      action           = "Redirected"
                       / "Expanded"
                       / "Relayed"
                       / "Rerouted"

   If MTA.PerMessageTransferFields.deferred-delivery-time is present,
   use it to generate a Deferred-Delivery: field.  For some reason,
   X.400 does not make this information available at the MTS level on
   delivery.  X.400 profiles, and in particular the CEN/CENELEC profile
   for X.400(1984) [Systems85a], specify that this element must be
   supported at the first MTA.  If it is not, the function may
   optionally be implemented by the gateway: that is, the gateway should
   hold the message until the time specified in the protocol element.
   Thus, it is expected that the value of this element will often be in
   the past.  For this reason, the extended RFC 822 field is primarily
   for information.

   Merge MTA.PerMessageTransferFields.trace-information, and
   MTA.PerMessageTransferFields.internal-trace-information to produce a
   single ordered trace list.  If Internal trace from other management
   domains has not been stripped, this may require complex interleaving.
   Use this to generate a sequence of "X400-Received:" fields.  The only
   difference between external trace and internal trace will be the



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   extra MTA information in internal trace elements.

   When generating an RFC 822 message all trace fields (X400- Received
   and Received) should be at the beginning of the header, before any
   other fields.  Trace should be in chronological order, with the most
   recent element at the front of the message.  A simple example trace
   (external) is:

   X400-Received: by /PRMD=UK.AC/ADMD=Gold 400/C=GB/ ; Relayed ;
           Tue, 20 Jun 89 19:25:11 +0100

   A more complex example (internal):

   X400-Received: by mta UK.AC.UCL.CS in
                                      /PRMD=UK.AC/ADMD=Gold 400/C=GB/ ;
           deferred until  Tue, 20 Jun 89 14:24:22 +0100 ;
           converted (undefined, g3fax) ";" attempted /ADMD=Foo/C=GB/ ;
           Relayed, Expanded, Redirected ; Tue, 20 Jun 89 19:25:11 +0100

5.3.8.  Mappings from Report Delivery

   Delivery reports are mapped at the MTS service level.  This means
   that only reports destined for the MTS user will be mapped.  Some
   additional services are also taken from the MTA service.

5.3.8.1.  MTS Mappings

   A Delivery Report service will be represented as
   MTS.ReportDeliveryEnvelope, which comprises of per-report-fields
   (MTS.PerReportDeliveryFields) and per-recipient-fields.

   A message should be generated with the following fields:

   From:
        An administrator at the gateway system.  This is also the
        822-MTS originator.

   To:  A mapping of the
        MTA.ReportTransferEnvelope.report-destination-name.  This is
        also the 822-MTS recipient.

   Message-Type:
        Set to "Delivery Report".

   Subject:
        Something of the form "X.400 Delivery Report".

   The format of the body of the message is defined to ensure that all



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   information is conveyed to the RFC 822 user in a consistent manner.
   This gives a summary of critical information, and then a full listing
   of all parameters:


   dr-body-format = dr-summary <CRLF>
                    dr-recipients <CRLF>
                    dr-extra-information <CRLF>
                    dr-content-return


   dr-content-return = "The Original Message is not available"
                   / "The Original Message follows:"
                     <CRLF> <CRLF> message

   dr-summary = "This report relates to your message:" <CRLF>
                content-correlator <CRLF> <CRLF>
                "of" date-time <CRLF> <CRLF>
                "It was generated by:" report-point <CRLF>
                "at" date-time <CRLF> <CRLF>
                "It was later converted to RFC 822 by:" mailbox <CRLF>
                "at" date-time <CRLF> <CRLF>


   dr-recipients = *(dr-recipient <CRLF> <CRLF>)

   dr-recipient = dr-recip-success / dr-recip-failure

   dr-recip-success =
                   "Your message was successfully delivered to:"
                   mailbox "at" date-time

   dr-recip-failure = "Your message was not delivered to:"
                   mailbox <CRLF>
                   "for the following reason:" *word


   dr-extra-information =
    "-----------------------------------------------" <CRLF> <CRLF>
    "The following information is derived from the Report" <CRLF>
    "It may be useful for problem diagnosis:" <CRLF> <CRLF>
    drc-field-list

   drc-field-list       = *(drc-field <CRLF>)

   drc-field = "Subject-Submission-Identifier" ":"
                           mts-msg-id
             / "Content-Identifier" ":" printablestring



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             / "Content-Type" ":" mts-content-type
             / "Original-Encoded-Information-Types" ":"
                           encoded-info
             / "Originator-and-DL-Expansion-History" ":"
                           dl-history
             / "Reporting-DL-Name" ":" mailbox
             / "Content-Correlator" ":" content-correlator
             / "Recipient-Info" ":" recipient-info
             / "Subject-Intermediate-Trace-Information" ":"
                           x400-trace


   recipient-info  = mailbox "," std-or ";"
                   report-type
                   [ "converted eits" encoded-info ";" ]
                   [ "originally intended recipient"
                            mailbox "," std-or ";" ]
                   [ "last trace" [ encoded-info ] date-time ";" ]
                   [ "supplementary info" <"> printablestring <"> ";" ]
                   [ "redirection history" 1#redirection ";"
                   [ "physical forwarding address"
                                         printablestring ";" ]


   report-type     = "SUCCESS" drc-success
                   / "FAILURE" drc-failure

   drc-success     = "delivered at" date-time ";"
                   [ "type of MTS user" labelled-integer ";" ]

   drc-failure     = "reason" labelled-integer ";"
                   [ "diagnostic" labelled-integer ";" ]

   report-point = [ "mta" word "in" ] global-id
   content-correlator = *word
   dl-history = 1#( mailbox "(" date-time ")")

   The format is defined as a fixed definition.  The only exception is
   that the EBNF.drc-fields should follow RFC 822 folding rules.

   The elements of MTS.ReportDeliveryEnvelope.per-report-fields are
   mapped as follows onto extended RFC 822 fields:

   subject-submission-identifier
        Mapped to EBNF.drc-field (Subject-Submission-Identifier)

   content-identifier
        Mapped to EBNF.drc-field (Content-Identifier)



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   content-type
        Mapped to EBNF.drc-field (Content-Type)

   original-encoded-information-types
        Mapped to EBNF.drc-field (Encoded-Info)

   The extensions from
   MTS.ReportDeliveryEnvelope.per-report-fields.extensions are
   mapped as follows:

   originator-and-DL-expansion-history
        Mapped to EBNF.drc-field (Originator-and-DL-Expansion-
        History)

   reporting-DL-name
        Mapped to EBNF.drc-field (Reporting-DL-Name)

   content-correlator
        Mapped to EBNF.content-correlator, provided that the
        encoding is IA5String (this should always be the case).
        This is used in EBNF.dr-summary and EBNF.drc-field-list.
        In the former, LWSP may be added, in order to improve the
        layout of the message.

   message-security-label
   reporting-MTA-certificate
   report-origin-authentication-check

      These security parameters should not be present.  If they are,
      they should be discarded in preference to discarding the whole
      report.

   For each element of MTS.ReportDeliveryEnvelope.per-recipient-fields,
   a value of EBNF.dr-recipient, and an EBNF.drc-field (Recipient-Info)
   should be generated.  The components are mapped as follows.

   actual-recipient-name
        Used to generate the first EBNF.mailbox and EBNF.std-or in
        EBNF.recipient-info.  Both RFC 822 and X.400 forms are
        given, as there may be a problem in the mapping tables.  It
        also generates the EBNF.mailbox in EBNF.dr-recip-success or
        EBNF.dr-recip-failure.

   report
        If it is MTS.Report.delivery, then set EBNF.dr-recipient to
        EBNF.dr-recip-success, and similarly set EBNF.report-type,
        filling in EBNF.drc-success.  If it is a failure, set
        EBNF.dr-recipient to EBNF.dr-recip-failure, making a human



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        interpretation of the reason and diagnostic codes, and
        including any supplementary information.  EBNF.drc-failure
        should be filled in systematically.

   converted-encoded-information-types
        Set EBNF.drc-field ("converted eits")

   originally-intended-recipient
        Set the second ("originally intended recipient") mailbox

        and

        std-or in EBNF.drc-field.

   supplementary-info
        Set EBNF.drc-field ("supplementary info"), and include this
        information in EBNF.dr-recip-failure.

   redirection-history
        Set EBNF.drc-field ("redirection history")

   physical-forwarding-address
        Set ENBF.drc-field ("physical forwarding address")

   recipient-certificate
        Discard

   proof-of-delivery
        Discard

   Any unknown extensions should be discarded, irrespective of
   criticality.

   The original message should be included in the delivery port.  The
   original message will usually be available at the gateway, as
   discussed in Section 5.2.

5.3.8.2.  MTA Mappings

   The single 822-MTS recipient is constructed from
   MTA.ReportTransferEnvelope.report-destination-name, using the
   mappings of Chapter 4.  Unlike with a user message, this information
   is not available at the MTS level.

   The following additional mappings should be made:

   MTA.ReportTransferEnvelope.report-destination-name
        This should be used to generate the To: field.



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   MTA.ReportTransferEnvelope.identifier
        Mapped to the extended RFC 822 field "X400-MTS-Identifier:".
        It may also be used to derive a "Message-Id:" field.

   MTA.ReportTransferEnvelope.trace-information
        and

   MTA.ReportTransferEnvelope.internal-trace-information
        Mapped onto the extended RFC 822 field "X400-Received:", as
        described in Section 5.3.7.  The first element should also
        be used to generate the "Date:" field, and the
        EBNF.failure-point.

      MTA.PerRecipientReportTransferFields.last-trace-information
      Mapped to EBNF.recipient-info (last trace)
      MTA.PerReportTransferFields.subject-intermediate-trace-information
      Mapped to EBNF.drc-field (subject-Intermediate-Trace-Information).
      These fields should be ordered so that the most recent trace element
      comes first.

5.3.8.3.  Example Delivery Report

   This is an example, of a moderately complex report.

   From: The Postmaster <postmaster@cs.ucl.ac.uk>
   To: jpo@computer-science.nottingham.ac.uk
   Subject: X.400 Delivery Report
   Message-Type: Delivery Report
   Date: Wed, 21 Jun 89 08:45:25 +0100
   X400-MTS-Identifier: /PRMD=UK.AC/ADMD=Gold 400/C=GB/;13412345235

   This report relates to your message:
     Date: Wed, 21 Jun 89 06:15:43 +0000
     Message-ID:  <8907140715.aa09015@CS.Nott.AC.UK>
     Subject: Now it's the fine tuning .... !
     To: Piete Brooks (Postmaster) <pb@computer-lab.cambridge.ac.uk>

   of Wed, 21 Jun 89 06:15:43 +0000

   It was generated by mta PK in /PRMD=UK/ADMD=DBP/C=DE/
   at Wed, 21 Jun 89 08:45:25 +0100

   It was later converted to RFC 822 by: Mail-Gateway@oxbridge.ac.uk
   at Wed, 21 Jun 89 08:45:26 +0100

   Your message was not delivered to: bad-user@nowhere
   for the following reason: Rendition problem with punctuation
           (Umlaut failure)



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   -----------------------------------------------

   The following information is derived from the Report
   It may be useful for problem diagnosis:

   Subject-Submission-Identifier:
                          [/PRMD=UK.AC/ADMD=Gold 400/C=GB/;148996]
   Content-Identifier:  X.400 Delivery Report
   Content-Type: P2-1988 (22)
   Original-Encoded-Information-Types: ia5
   Content-Correlator: Date: Wed, 21 Jun 89 06:15:43 +0000
       Message-ID:  <8907140715.aa09015@CS.Nott.AC.UK>
       Subject: Now it's the fine tuning .... !
       To: Piete Brooks (Postmaster) <pb@computer-lab.cambridge.ac.uk>
   Recipient-Info:
       bad-user@nowhere, /S=bad-user/PRMD=nowhere/ADMD=DBP/C=DE/ ;
       FAILURE reason Physical-Rendition-Not-Performed (3) ;
       diagnostic Punctuation-Symbol-Loss (23) ;
       supplementary info Umlaut failure

   The Original Message follows:

   Subject: Now it's the fine tuning .... !
   Date: Wed, 21 Jun 89 06:15:43 +0000
   From: Julian Onions <jpo@computer-science.nottingham.ac.uk>
   To: Piete Brooks (Postmaster) <pb@computer-lab.cambridge.ac.uk>
   Cc: bad-user@nowhere
   Message-ID:  <8907140715.aa09015@CS.Nott.AC.UK>

   A short test

5.3.9.  Probe

   This is an MTS internal issue.  Any probe should be serviced by the
   gateway, as there is no equivalent RFC 822 functionality.  The value
   of the reply is dependent on whether the gateway could service an MTS
   Message with the values specified in the probe.  The reply should
   make use of MTS.SupplementaryInformation to indicate that the probe
   was serviced by the gateway.

Appendix A - Differences with RFC 987

   This appendix summarises changes between this document and RFC
   987/RFC 1026.

1.  Introduction

   The model has shifted from a protocol based mapping to a service



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   based mapping.  This has increased the generality of the
   specification, and improved the model.  This change affects the
   entire document.

   A restriction on scope has been added.

2.  Service Elements

      -    The new service elements of X.400 are dealt with.

      -    A clear distinction is made between origination and
           reception.

3.  Basic Mappings

      -    Add teletex support.

      -    Add object identifier support.

      -    Add labelled integer support.

      -    Make PrintableString <-> ASCII mapping reversible.

      -    The printable string mapping is aligned to the NBS mapping
           derived from RFC 987.

4.  Addressing

      -    Support for new addressing attributes.

      -    The message ID mapping is changed to not be table driven.

5.  Detailed Mappings

      -    Define extended IPM Header, and use instead of second body
           part for RFC 822 extensions.

      -    Realignment of element names.

      -    New syntax for reports, simplifying the header and
           introducing a mandatory body format (the RFC 987 header
           format was unusable).

      -    Drop complex autoforwarded mapping.

      -    Add full mapping for IP Notifications, defining a body
           format.




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      -    Adopt an MTS Identifier syntax in line with the O/R Address
           syntax.

      -    A new format for X400 Trace representation on the RFC 822
           side.

6.  Appendices

      -    Move Appendix on restricted 822 mappings to a separate RFC.

      -    Delete Phonenet and SMTP Appendixes.

Appendix B - Mappings specific to the JNT Mail

   This Appendix is specific to the JNT Mail Protocol.  It describes
   specific changes in the context of this protocol.

1.  Introduction

   There are five aspects of a gateway which are JNT Mail Specific.
   These are each given a section of this appendix.

2.  Domain Ordering

   When interpreting and generating domains, the UK NRS domain ordering
   must be used.

3.  Acknowledge-To:

   This field has no direct functional equivalent in X.400.  However, it
   can be supported to an extent, and can be used to improve X.400
   support.

   If an Acknowledge-To: field is present when going from JNT Mail to
   X.400, MTS.PerRecipientSubmissionFields.originator-request-
   report.report shall be set for each recipient.  If there is more that
   one address in the Acknowledge-To: field, or if the one address is
   not equivalent to the 822-MTS return address, then:

      1.   Acknowledgement(s) should be generated by the gateway.  The
           text of these acknowledgements should indicate that they are
           generated by the gateway.

      2.   The Acknowledge-To: field should also be passed as an
           extension heading.

   When going from X.400 to JNT Mail, in cases where
   MTA.PerRecipientMessageTransferFields.per-recipient-indicators.



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   originator-report is set, the copy of the message to that recipient
   should have an Acknowledge-To: field containing the
   MTS.OtherMessageDeliveryFields.originator-name.  No special treatment
   should be given when MTA.PerRecipientMessageTransferFields.per-
   recipient-indicators.  originating-MTA-report is set.  No attempt
   should be made to map Receipt notification requests onto
   Acknowledge-To:, as no association can be guaranteed between IPMS and
   MTS level addressing information.

4.  Trace

   JNT Mail trace uses the Via: syntax.  When going from JNT Mail to
   X.400, a mapping similar to that for Received:  is used. No
   MTS.GlobalDomainIdentifier of the site making the trace can be
   derived from the Via:, so a value for the gateway should be used.
   The trace text, including the "Via:", should be unfolded, truncated
   to MTS.ub-mta-name-length (32), and mapped to
   MTA.InternalTraceInformationElement.mta-name.  There is no JNT Mail
   specific mapping for the reverse direction.

5.  Timezone specification

   The extended syntax of zone defined in the JNT Mail Protocol should
   be used in the mapping of UTCTime defined in Chapter 3.

6.  Lack of 822-MTS originator specification

   In JNT Mail the default mapping of the
   MTS.OtherMessageDeliveryFields.originator-name is to the Sender:
   field.  This can cause a problem when going from X.400 to JNT Mail if
   the mapping of IPMS.Heading has already generated a Sender: field.
   To overcome this, new extended JNT Mail field is defined.  This is
   chosen to align with the JNT recommendation for interworking with
   full RFC 822 systems [Kille84b].

      original-sender     = "Original-Sender" ":" mailbox

   If an IPM has no IPMS.Heading.authorising-users component and
   IPMS.Heading.originator.formal-name is different from
   MTS.OtherMessageDeliveryFields.originator-name, map
   MTS.OtherMessageDeliveryFields.originator-name, onto the Sender:
   field.

   If an IPM has a IPMS.Heading.authorising-users component, and
   IPMS.Heading.originator.formal-name is different from
   MTS.OtherMessageDeliveryFields.originator-name,
   MTS.OtherMessageDeliveryFields.originator-name should be mapped onto
   the Sender: field, and IPMS.Heading.originator mapped onto the



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   Original-Sender: field.

   In other cases the MTS.OtherMessageDeliveryFields.originator-name, is
   already correctly represented.

Appendix C - Mappings specific to UUCP Mail

   Gatewaying of UUCP and X.400 is handled by first gatewaying the UUCP
   address into RFC 822 syntax (using RFC 976) and then gatewaying the
   resulting RFC 822 address into X.400.  For example, an X.400 address:

      Country         US
      Organisation    Xerox
      Personal Name   John Smith

   might be expressed from UUCP as

      inthop!gate!gatehost.COM!/C=US/O=Xerox/PN=John.Smith/

   (assuming gate is a UUCP-Internet gateway and gatehost.COM is an
   Internet-X.400 gateway) or

      inthop!gate!Xerox.COM!John.Smith

   (assuming that Xerox.COM and /C=US/O=Xerox/ are equivalent.)

   In the other direction, a UUCP address Smith@ATT.COM, integrated into
   822, would be handled as any other 822 address.  A non-integrated
   address such as inthop!dest!user might be handled through a pair of
   gateways:

      Country         US
      ADMD            ATT
      PRMD            Internet
      Organisation    GateOrg
      RFC-822         inthop!dest!user@gatehost.COM

   or through a single X.400 to UUCP gateway:

      Country         US
      ADMD            ATT
      PRMD            UUCP
      Organisation    GateOrg
      RFC-822         inthop!dest!user

Appendix D - Object Identifier Assignment

   An object identifier is needed for the extension IPMS element.  The



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   following value should be used.

      rfc-987-88 OBJECT IDENTIFIER ::=
          {ccitt data(9) pss(2342) ucl(234219200300) rfc-987-88(200)}

      id-rfc-822-field OBJECT IDENTIFIER ::= {rfc987-88 field(0)}

Appendix E - BNF Summary

   boolean = "TRUE" / "FALSE"


   numericstring = *DIGIT


   printablestring  = *( ps-char )
   ps-restricted-char      = 1DIGIT /  1ALPHA / " " / "'" / "+"
                      / "," / "-" / "." / "/" / ":" / "=" / "?"
   ps-delim         = "(" / ")"
   ps-char          = ps-delim / ps-restricted-char


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


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


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


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

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


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



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

   defined-value ::= key-string

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


   encoded-info    = 1#encoded-type

   encoded-type    = built-in-eit / object-identifier

   built-in-eit    = "Undefined"         ; undefined (0)
                   / "Telex"             ; tLX (1)
                   / "IA5-Text"          ; iA5Text (2)
                   / "G3-Fax"            ; g3Fax (3)
                   / "TIF0"              ; tIF0 (4)
                   / "Teletex"           ; tTX (5)
                   / "Videotex"          ; videotex (6)
                   / "Voice"             ; voice (7)
                   / "SFD"               ; sFD (8)
                   / "TIF1"              ; tIF1 (9)


   encoded-pn      = [ given "." ] *( initial "." ) surname

   given           = 2*<ps-char not including ".">

   initial         = ALPHA

   surname         = printablestring


   std-or-address  = 1*( "/" attribute "=" value ) "/"
   attribute       = standard-type
                   / "RFC-822"
                   / registered-dd-type
                   / dd-key "." std-printablestring
   standard-type   = key-string

   registered-dd-type
                   = key-string
   dd-key          = key-string

   value           = std-printablestring

   std-printablestring
                   = *( std-char / std-pair )



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   std-char        = <"{", "}", "*", and any ps-char
                                 except "/" and "=">
   std-pair        = "$" ps-char


   dmn-or-address  = dmn-part *( "." dmn-part )
   dmn-part        = attribute "$" value
   attribute       = standard-type
                   / "~" dmn-printablestring
   value           = dmn-printablestring
                   / "@"
   dmn-printablestring =
                   = *( dmn-char / dmn-pair )
   dmn-char        = <"{", "}", "*", and any ps-char
                                         except ".">
   dmn-pair        = "."


   global-id = std-or-address


   mta-field       = "X400-Received" ":" x400-trace
                   / "Deferred-Delivery" ":" date-time
                   / "Latest-Delivery-Time" ":" date-time


   x400-trace       = "by" md-and-mta ";"
                    [ "deferred until" date-time ";" ]
                    [ "converted" "(" encoded-info ")" ";" ]
                    [ "attempted" md-and-mta ";"  ]
                       action-list
                       ";" arrival-time


   md-and-mta       = [ "mta" mta "in" ]  global-id
   mta              = word
   arrival-time     = date-time


   action-list      = 1#action
   action           = "Redirected"
                    / "Expanded"
                    / "Relayed"
                    / "Rerouted"


   dr-body-format = dr-summary <CRLF>
                    dr-recipients <CRLF>



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                    dr-extra-information <CRLF>
                    dr-content-return


   dr-content-return = "The Original Message is not available"
                   / "The Original Message follows:"
                     <CRLF> <CRLF> message

   dr-summary = "This report relates to your message:" <CRLF>
                   content-correlator <CRLF> <CRLF>
                "of" date-time <CRLF> <CRLF>
                "It was generated by:" report-point <CRLF>
                "at" date-time <CRLF> <CRLF>
                "It was later converted to RFC 822 by:" mailbox <CRLF>
                "at" date-time <CRLF> <CRLF>


   dr-recipients = *(dr-recipient <CRLF> <CRLF>)

   dr-recipient = dr-recip-success / dr-recip-failure

   dr-recip-success =
                   "Your message was successfully delivered to:"
                   mailbox "at" date-time


   dr-recip-failure = "Your message was not delivered to:"
                           mailbox <CRLF>
                      "for the following reason:" *word


   dr-extra-information =
    "-----------------------------------------------" <CRLF> <CRLF>
    "The following information is derived from the Report" <CRLF>

    "It may be useful for problem diagnosis:" <CRLF> <CRLF>
   drc-field-list

   drc-field-list       = *(drc-field <CRLF>)

   drc-field = "Subject-Submission-Identifier" ":"
                                   mts-msg-id
             / "Content-Identifier" ":" printablestring
             / "Content-Type" ":" mts-content-type
             / "Original-Encoded-Information-Types" ":"
                           encoded-info
             / "Originator-and-DL-Expansion-History" ":"
                           dl-history



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             / "Reporting-DL-Name" ":" mailbox
             / "Content-Correlator" ":" content-correlator
             / "Recipient-Info" ":" recipient-info


   recipient-info  = mailbox "," std-or ";"
                   report-type
                   [ "converted eits" encoded-info ";" ]
                   [ "originally intended recipient"
                           mailbox "," std-or ";" ]
                   [ "supplementary info" <"> printablestring <"> ";" ]
                   [ "redirection history" 1#redirection ";"
                   [ "physical forwarding address"
                                         printablestring ";" ]


   report-type     = "SUCCESS" drc-success
                   / "FAILURE" drc-failure

   drc-success     = "delivered at" date-time ";"
                   [ "type of MTS user" labelled-integer ";" ]

   drc-failure     = "reason" labelled-integer ";"
                   [ "diagnostic" labelled-integer ";" ]


   report-point = [ "mta" word "in" ] global-id
   content-correlator = *word
   dl-history = 1#( mailbox "(" date-time ")")


   mts-field = "X400-MTS-Identifier" ":" mts-msg-id
             / "X400-Originator" ":" mailbox
             / "X400-Recipients" ":" 1#mailbox
             / "Original-Encoded-Information-Types" ":"

                               encoded-info
             / "X400-Content-Type" ":" mts-content-type
             / "Content-Identifier" ":" printablestring
             / "Priority" ":" priority
             / "Originator-Return-Address" ":" 1#mailbox
             / "DL-Expansion-History" ":" mailbox ";" date-time ";"
             / "Redirection-History" ":" redirection
             / "Conversion" ":" prohibition
             / "Conversion-With-Loss" ":" prohibition
             / "Requested-Delivery-Method" ":"
                             1*( labelled-integer )
             / "Delivery-Date" ":" date-time



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             / "Discarded-X400-MTS-Extensions" ":"
                             1#( oid / labelled-integer )


   prohibition     = "Prohibited" / "Allowed"

   mts-msg-id       = "[" global-id ";" *text "]"

   mts-content-type = "P2" /  labelled-integer
                   / object-identifer

   priority        = "normal" / "non-urgent" / "urgent"

   redirection     = mailbox ";" "reason" "="
                           redirection-reason
                           ";" date-time
   redirection-reason =
             "Recipient Assigned Alternate Recipient"
           / "Originator Requested Alternate Recipient"
           / "Recipient MD Assigned Alternate Recipient"


   ipn-body-format = ipn-description <CRLF>
                   [ ipn-extra-information <CRLF> ]
                   ipn-content-return

   ipn-description = ipn-receipt / ipn-non-receipt

   ipn-receipt = "Your message to:" preferred-recipient <CRLF>
            "was received at" receipt-time <CRLF> <CRLF>
            "This notification was generated"
            acknowledgement-mode <CRLF>
            "The following extra information was given:" <CRLF>
            ipn-suppl <CRLF>

   ipn-non-receipt "Your message to:"

            preferred-recipient <CRLF>
            ipn-reason


   ipn-reason = ipn-discarded / ipn-auto-forwarded

   ipn-discarded = "was discarded for the following reason:"
                   discard-reason <CRLF>

   ipn-auto-forwarded = "was automatically forwarded." <CRLF>
                   [ "The following comment was made:"



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                           auto-comment ]


   ipn-extra-information =
            "The following information types were converted:"
            encoded-info

   ipn-content-return = "The Original Message is not available"
                   / "The Original Message follows:"
                   <CRLF> <CRLF> message


   preferred-recipient = mailbox
   receipt-time        = date-time
   auto-comment        = printablestring
   ipn-suppl           = printablestring


   non-receipt-reason = "Discarded" / "Auto-Forwarded"

   discard-reason     = "Expired" / "Obsoleted" /
                           "User Subscription Terminated"

   acknowledgement-mode = "Manually" / "Automatically"


   ms-field = "Obsoletes" ":" 1#msg-id
            / "Expiry-Date" ":" date-time
            / "Reply-By" ":" date-time
            / "Importance" ":" importance
            / "Sensitivity" ":" sensitivity
            / "Autoforwarded" ":" boolean
            / "Incomplete-Copy" ":"
            / "Language" ":" language
            / "Message-Type" ":" message-type
            / "Discarded-X400-IPMS-Extensions" ":" 1#oid

   importance      = "low" / "normal" / "high"


   sensitivity     = "Personal" / "Private" /
                          "Company-Confidential"

   language        = 2*ALPHA [ language-description ]
   language-description = printable-string


   message-type    = "Delivery Report"



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                   / "InterPersonal Notification"
                   / "Multiple Part"


Appendix F - Format of address mapping tables

   There is a need to specify the association between the domain and
   X.400 namespaces described in Chapter 4.  The use of this association
   leads to a better service on both sides of the gateway, and so
   defining mappings and distributing them in the form defined in this
   appendix is strongly encouraged.

   This syntax defined is initially in table form, but the syntax is
   defined in a manner which makes it suitable for use with domain
   nameservices (such as the Internet Domain nameservers or the UK NRS).
   The mapping is not symmetric, and so a separate table is specified
   for each direction.  If multiple matches are possible, the longest
   possible match should be used.

   First, an address syntax is defined, which is compatible with the
   syntax used for 822.domains.  It is intended that this syntax may be
   used in conjunction with systems which support this form of name.

   To allow the mapping of null attributes  to be represented, the
   pseudo-value "@" (not a printable string character) is used to
   indicate omission of a level in the hierarchy.  This is distinct from
   the form including the element with no value, although a correct
   X.400 implementation will interpret both in the same manner.

   This syntax is not intended to be handled by users.

      dmn-or-address  = dmn-part *( "." dmn-part )
      dmn-part        = attribute "$" value
      attribute       = standard-type
                      / "~" dmn-printablestring
      value           = dmn-printablestring
                      / "@"

      dmn-printablestring =
                          = *( dmn-char / dmn-pair )
      dmn-char        = <"{", "}", "*", and any ps-char
                                              except ".">
      dmn-pair        = "."

      An example usage:

      ~ROLE$Big.Chief.ADMD$ATT.C$US
      PRMD$DEC.ADMD$@.C$US



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   The first example illustrates quoting of a ".", and the second
   omission of the ADMD level.

   Various further restrictions are placed on the usage of dmn-or-
   address:

   1.   Only C, ADMD, PRMD, O, and OU may be used.

   2.   There must be a strict ordering of all components, with the
        most significant components on the RHS.

   3.   No components may be omitted from the hierarchy, although
        the hierarchy may terminate at any level.  If the mapping is
        to an omitted component, the "@" syntax is used.

   For domain -> X.400:

          domain-syntax "#" dmn-or-address "#"

   Note that the trailing "#" is used for clarity, as the dmn-or-
   address syntax can lead to values with trailing blanks.   Lines
   staring with "#" are comments.

      For example:

      AC.UK#PRMD$UK.AC.ADMD$GOLD 400.C$GB#
      XEROX.COM#O$Xerox.ADMD$ATT.C$US#
      GMD.DE#O$@.PRMD$GMD.ADMD$DBP.C$DE#

   For X.400 -> domain:

      dmn-or-address "#" domain-syntax "#"

      For example:

      #
      # Mapping table
      #
      PRMD$UK.AC.ADMD$GOLD 400.C$GB#AC.UK#

References

   [Braden89a]  Braden, R., Editor, "Requirements for Internet Hosts --
   Application and Support", RFC 1123, USC/Information Sciences
   Institute, October 1989.

   [CCITT88a]  CCITT, "CCITT Recommendations X.408", Message Handling
   Systems: Encoded Information Type Conversion Rules, CCITT, December



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   1988.

   [CCITT/ISO88a]  CCITT/ISO, "CCITT Recommendations X.400/ ISO IS
   10021-1", Message Handling: System and Service Overview, CCITT/ISO,
   December 1988.

   [CCITT/ISO88b]  CCITT/ISO, "CCITT Recommendations X.420/ ISO IS
   10021-7", Message Handling Systems: Interpersonal Messaging System,
   CCITT/ISO, December 1988.

   [CCITT/ISO88c]  CCITT/ISO, "CCITT Recommendations X.411/ ISO IS
   10021-4", Message Handling Systems: Message Transfer System: Abstract
   Service Definition and Procedures, CCITT/ISO, December 1988.

   [CCITT/ISO88d]  CCITT/ISO, "Specification of Abstract Syntax Notation
   One (ASN.1)", CCITT Recommendation X.208 / ISO IS 8824, CCITT/ISO,
   December 1988.

   [Crocker82a]  Crocker, D., "Standard of the Format of ARPA Internet
   Text Messages", RFC 822, August 1982.

   [Horton86a]  Horton, M., "UUCP Mail Interchange Format Standard", RFC
   976, February 1986.

   [Kille84b]  Kille, S., "Gatewaying between RFC 822 and JNT Mail", JNT
   Mailgroup Note 15, May 1984.

   [Kille84a]  Kille, S., Editor, "JNT Mail Protocol (revision 1.0)",
   Joint Network Team, Rutherford Appleton Laboratory, March 1984.

   [Kille86a]  Kille, S., "Mapping Between X.400 and RFC 822",  UK
   Academic Community Report (MG.19) / RFC 987, June 1986.

   [Kille87a]  Kille, S., "Addendum to RFC 987", UK Academic Community
   Report (MG.23) / RFC 1026, August 1987.

   [Kille89a]  Kille, S., "A String Encoding of Presentation Address",
   UCL Research Note 89/14, March 1989.

   [Kille89b]  Kille, S., "Mapping Between Full RFC 822 and RFC 822 with
   Restricted Encoding", RFC 1137, December 1989.

   [Larmouth83a]  Larmouth, J., "JNT Name Registration Technical Guide",
   Salford University Computer Centre, April 1983.

   [Mockapetris87a]  Mockapetris, P., "Domain Names - Concepts and
   Facilities", RFC 1034, USC/Information Sciences Institute, November
   1987.



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   [Postel82a]  Postel, J., "Simple Mail Transfer Protocol", RFC 821,
   USC/Information Sciences Institute, August 1982.

   [Rose85a]  Rose M., and E. Stefferud, "Proposed Standard for Message
   Encapsulation", RFC 934, January 1985.

   [Systems85a]  CEN/CENELEC/Information Technology/Working Group on
   Private Message Handling Systems, "FUNCTIONAL STANDARD A/3222",
   CEN/CLC/IT/WG/PMHS N 17, October 1985.

Security Considerations

   Security issues are not discussed in this memo.

Author's Address

   Steve Kille
   University College London
   Gower Street
   WC1E 6BT
   England

   Phone: +44-1-380-7294

   EMail: S.Kille@Cs.Ucl.AC.UK


























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