RFC 2156
MIXER (Mime Internet X.400 Enhanced Relay): Mapping between X.400 and RFC 822/MIME
Pages: 144
Proposed Standard
Obsoletes: 0987 1026 1138 1148 1327 1495
Updates: 0822
Proposed Standard
Obsoletes: 0987 1026 1138 1148 1327 1495
Updates: 0822
Part 1 of 5 – Pages 1 to 27
Network Working Group S. Kille Request for Comments: 2156 Isode Ltd. Obsoletes: 987, 1026, 1138, 1148, 1327, 1495 January 1998 Updates: 822 Category: Standards Track MIXER (Mime Internet X.400 Enhanced Relay): Mapping between X.400 and RFC 822/MIME Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (1998). All Rights Reserved. Table of Contents 1 - Overview ...................................... 3 1.1 - X.400 ......................................... 3 1.2 - RFC 822 and MIME .............................. 3 1.3 - The need for conversion ....................... 4 1.4 - General approach .............................. 4 1.5 - Gatewaying Model .............................. 5 1.6 - Support of X.400 (1984) ....................... 8 1.7 - X.400 (1992) .................................. 8 1.8 - MIME .......................................... 8 1.9 - Body Parts .................................... 8 1.10 - Local and Global Scenarios .................... 9 1.11 - Compatibility with previous versions .......... 10 1.12 - Aspects not covered ........................... 10 1.13 - Subsetting .................................... 11 1.14 - Specification Language ........................ 11 1.15 - Related Specifications ........................ 11 1.16 - Document Structure ............................ 12 1.17 - Acknowledgements .............................. 12 2 - Service Elements .............................. 13 2.1 - The Notion of Service Across a Gateway ........ 13 2.2 - RFC 822 ....................................... 15 2.3 - X.400 ......................................... 18 3 - Basic Mappings ................................ 27 3.1 - Notation ...................................... 27
3.2 - ASCII and IA5 ................................. 29 3.3 - Standard Types ................................ 29 3.4 - Encoding ASCII in Printable String ............ 33 3.5 - RFC 1522 ...................................... 34 4 - Addressing and Message IDs .................... 35 4.1 - A textual representation of MTS.ORAddress ..... 36 4.2 - Global Address Mapping ........................ 43 4.3 - EBNF.822-address <-> MTS.ORAddress ............ 46 4.4 - Repeated Mappings ............................. 59 4.5 - Directory Names ............................... 62 4.6 - MTS Mappings .................................. 62 4.7 - IPMS Mappings ................................. 67 5 - Detailed Mappings ............................. 71 5.1 - RFC 822 -> X.400: Detailed Mappings ........... 71 5.2 - Return of Contents ............................ 86 5.3 - X.400 -> RFC 822: Detailed Mappings ........... 86 Appendix A - Mappings Specific to SMTP ..................... 114 1 - Probes ........................................ 114 2 - Long Lines .................................... 114 3 - SMTP Extensions ............................... 114 3.1 - SMTP Extension mapping to X.400 ............... 114 3.2 - X.400 Mapping to SMTP Extensions .............. 115 Appendix B - Mapping with X.400(1984) ...................... 116 Appendix C - RFC 822 Extensions for X.400 access ........... 118 Appendix D - Object Identifier Assignment .................. 119 Appendix E - BNF Summary ................................... 120 Appendix F - Text format for MCGAM distribution ............ 127 1 - Text Formats .................................. 127 2 - Mechanisms to register and to distribute MCGAMs ........................................ 127 3 - Syntax Definitions ............................ 128 4 - Table Lookups ................................. 129 5 - Domain -> OR Address MCGAM format ............. 129 6 - OR Address -> Domain MCGAM format ............. 129 7 - Domain -> OR Address of Preferred Gateway table ......................................... 130 8 - OR Addresss -> domain of Preferred Gateway table ......................................... 130 Appendix G - Conformance ................................... 131 Appendix H - Change History: RFC 987, 1026, 1138, 1148 ............................................... 133 1 - Introduction .................................. 133 2 - Service Elements .............................. 133 3 - Basic Mappings ................................ 133 4 - Addressing .................................... 134 5 - Detailed Mappings ............................. 134 6 - Appendices .................................... 134 Appendix I - Change History: RFC 1148 to RFC 1327 .......... 135
1 - General ....................................... 135 2 - Basic Mappings ................................ 135 3 - Addressing .................................... 135 4 - Detailed Mappings ............................. 135 5 - Appendices .................................... 136 Appendix J - Change History: RFC 1327 to this Document ............................................... 137 1 - General ....................................... 137 2 - Service Elements .............................. 137 3 - Basic Mappings ................................ 137 4 - Addressing .................................... 137 5 - Detailed Mappings ............................. 138 6 - Appendices .................................... 138 Appendix L - ASN.1 Summary ................................. 139 Security Considerations .................................... 141 Author's Address ........................................... 141 References ................................................. 141 Full Copyright Statement ................................... 144 Chapter 1 -- Overview 1.1. X.400 This document relates primarily to the ITU-T 1988 and 1992 X.400 Series Recommendations / ISO IEC 10021 International Standard. This ISO/ITU-T standard is referred to in this document as "X.400", which is a convenient shorthand. Any reference to the 1984 Recommendations will be explicit. Any mappings relating to elements which are in the 1992 version and not in the 1988 version will be noted explicitly. 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, such as EDI as defined in X.435. 1.2. RFC 822 and MIME RFC 822 evolved as a messaging standard on the DARPA (the US Defense Advanced Research Projects Agency) Internet. RFC 822 specifies an end to end message format, consisting of a header and an unstructured text body. MIME (Multipurpose Internet Mail Extensions) specifies a structured message body format for use with RFC 822. The term "RFC 822" is used in this document to refer to the combination of MIME and RFC 822. RFC 822 and MIME are used in conjunction with a number of different message transfer protocol environments. The core of the MIXER specification is designed to work with any supporting message transfer protocol.
One transfer protocol, SMTP, is of particular importance and is covered in MIXER. On the Internet and other TCP/IP networks, RFC 822 is used in conjunction with RFC 821, also known as Simple Mail Transfer Protocol (SMTP) [30], in a manner conformant with the host requirements specification [10]. Use of MIXER with SMTP is defined in Appendix A. 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 between the different technologies, 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 mapping between RFC 822 and X.400. This is standard usage amongst mail implementors, but differs from that used 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 to discard information in the objects it processes. This includes requested services which cannot be fully mapped.
4. Mail gateways operate at a level above the layer on which
they perform mappings. This implies that the gateway shall
not only be cognisant of the semantics of objects at the
gateway level, but also be cognisant of higher level
semantics. If meaningful transformation of the objects that
the gateway operates on is to occur, then the gateway needs
to understand more than the objects themselves.
5. Subject to 1), the mapping 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 , [11] 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 forwarded Interpersonal 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.
These IPMS Services utilise the Message Transfer System (MTS) Abstract Service [12]. The MTS 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). The Envelope includes a message identifier, an originator, and a list of recipients. Submission also includes the probe service, which supports the MTS Probe. Delivery also includes Reports, which indicate whether a given MTS Message has been delivered or not (or for a probe if delivery would have happened). The MTS is provided by MTAs which interact using the MTA (Message Transfer Agent) Service, which defines the interaction between MTAs, along with the procedures for distributed operation. This service provides for transfer of MTS Messages, Probes, and Reports. 1.5.2. RFC 822 RFC 822 is based on the assumption that there is an underlying service, which is here called the 822-MTS service. The 822-MTS service provides three basic functions: 1. Identification of a list of recipients. 2. Identification of an error return address. 3. Transfer of an RFC 822 message. It is possible to achieve 2) within the RFC 822 header. This specification will be used most commonly with SMTP as the 822- MTS service. The core MIXER specification is written so that it does not rely on non-basic 822-MTS services. Use of non-basic SMTP services is described in Appendix A. The core of this document is written using SMTP terminology for 822-MTS services. 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 IPM
heading fields, although some are analogous to MTS Service Elements or MTA Service Elements. RFC 822 supports delivery status notifications by use of the NOTARY mechanisms [28]. 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 SMTP (822-MTS) service mapping onto the MTS Service Elements and RFC 822 mapping onto an IPM, but there is a not a clear match between these services. Another elegant approach would be to treat this document as the definition of an X.400 Access Unit (AU). In this case, the abstraction level is too high, and some necessary mapping function is lost. 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 + SMTP 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 SMTP information is always mapped into an IPM (MTA, MTS, and IPMS Services) and a Delivery Status Notification is mapped onto a Report. Going from X.400 to RFC 822, an RFC 822 message and the associated SMTP information may be derived from: 1. An IPN (MTA, MTS, and IPMS services) 2. An IPM (MTA, MTS, and IPMS services) A Report (MTA, and MTS Services) is mapped onto a delivery status notification. Probes (MTA Service) shall 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 shall be rejected at the gateway if no other gatewaying procedure is defined. This specification is concerned with X.400 IPMS. Future specifications may defined mappings for other X.400 content types.
1.5.4. Repeated Mappings The primary goal of this specification is to support single mappings, so that X.400 and RFC 822 users can communicate with maximum functionality. The mappings specified here are designed to work where a message traverses multiple times between X.400 and RFC 822. This is often essential, particularly in the case of distribution lists. However, in general, this will lead to a level of service which is the lowest common denominator (approximately the services offered by RFC 822). Some RFC 822 networks may wish to use X.400 as an interconnection mechanism (typically for policy reasons), and this is fully supported. Where an X.400 message transfers to RFC 822 and then back to X.400, there is no expectation of X.400 services which do not have an equivalent service in standard RFC 822 being preserved - although this may be possible in some cases. 1.6. Support of X.400 (1984) The MIXER definition is based on the initial specification of RFC 987 and in its addendum RFC 1026, which defined a mapping between X.400(1984) and RFC 822. The core MIXER mapping is defined using the full 1988 version of X.400, and not to a 1984 compatible subset. New features of X.400(1988) can be used to provide a much cleaner mapping than that defined in RFC 987. To interwork with 1984 systems, Appendix B shall be followed. If a message is being transferred to an X.400(1984) system by way of X.400(1988) MTA it will give a slightly better service to follow the rules of Appendix B, than to downgrade without this knowledge. Downgrading specifications which supplement those specified in X.400 (X.419) are given in RFC 1328 [22] and RFC 1496 (HARPOON) [5]. 1.7. X.400 (1992) X.400 (1992) features are not used by the core of this mapping, and so there is not an equivalent downgrade problem. 1.8. MIME MIME format messages are generated by this mapping. As MIME messages are fully RFC 822 compliant, this will not cause problems with systems which are not MIME capable.
1.9. Body Parts MIME and X.400 IPMS can both carry arbitrary body parts. MIME defines a mechanism for adding new body parts, and new body parts are registered with the IANA. X.400 defines a mechanism adding new body parts, usually referred to as Body Part 15. Extensions are defined by Object Identifiers, so there is no requirement for a central body part registration authority. The Electronic Messaging Association (EMA) maintains a list of some commonly used body parts. The EMA has specified a mechanism to use the File Transfer Body Part (FTBP) as a more generic means to support message attachments. This approach is gaining widespread commercial support. The mapping between X.400 and MIME body parts is defined in the companion MIXER specification, referenced here as RFC 2157 [8]. This document is an update of RFC 1494 [6]. Editor's Note: References to 2157 will be resolved as these two documents are expected to progress in parallel. These two specifications together form the complete MIXER Mapping. 1.10. Local and Global Scenarios There are two basic scenarios for X.400/MIME interworking: Global Scenario There are two global mail networks (Internet/MIME and X.400), interconnected by multiple gateways. Objects may be transferred over multiple gateways, and so it is important that gateways behave in a coherent fashion. MIXER is critical to support this scenario. Local Scenario A gateway is used to connect a closed community to a global mail network (this could be enforced by connectivity or gateway authorisation policy). This is a common commercial scenario. MIXER is useful to support this scenario, as it allows an industry standard provision of service, but this could be supported by something which was MIXER-like. A solution for the global scenario will work for the local scenario. However, there are aspects of MIXER which have significant implementation or deployment effort (the global mapping is the major one, but there are other details too) which and are needed to support
the global scenario, but are not needed in the local scenario. Note that the local scenario may be the driving force for most deployments, and support of the global scenario may be an important secondary goal. There is also a transition effect. Gateways which are initially deployed in a strict local scenario situation start to find themselves in a global scenario. A common case is ADMD provided gateways, which are targeted strictly at the local scenario. In practice they soon start to operate in the global scenario, because of distribution lists and messages exchanged with X.400 users that are not customers of the ADMD. At this point, users are hurt by the restrictions of a local scenario gateway. Note that conformance to MIXER applies to an instantiation of a gateway, not just an implementation (although clearly it is critical that the implementation is capable of being operated in a conformant manner). MIXER's conformance target is the global scenario, and the specification of MIXER defines operation in this way. 1.11. Compatibility with previous versions The changes between this and older versions of the document are given in Appendices H, I and J. These are RFCs 987, 1026, 1138, 1148 and 1327. This document is a revision of RFC 1327 [21]. As far as possible, changes have been made in a compatible fashion. 1.12. Aspects not covered There have been a number of cases where previous versions of this document were 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 MIXER as
an interface - there are too many aspects of X.400 which cannot be accessed through it. If a text interface is desired, a specification targeted at X.400, without RFC 822 restrictions, would be more appropriate. Some optional and limited extensions in this area have proved useful, and are defined in Appendix C. 1.13. 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 non-conformant and strongly discouraged. 1.14. Specification Language ISO and Internet standards have clear definitions as to the style of language used. This specification maps between ISO/ITU-T protocol and Internet protocols. This document uses ISO terminology for the following reasons: 1. This was done in previous versions. 2. ISO language may be mechanically converted to Internet language, but not vice versa. The key elements of the ISO rules are: 1. All mandatory features shall clearly be indicated by imperative statements or the word "shall" or "shall not". 2. Optional features shall be indicated by the word "may". 3. The word "should" and the phrase "may not" shall not be used. In some cases the specification issues guidance on use of optional features, by use of the the phrase word "recommended" or "not recommended". To interpet this document according to Internet rules, replace every occurrence of "shall" with "must". 1.15. Related Specifications Mappings between Mail-11 and X.400 and Mail-11 and RFC 822 are described in RFC 2162, using mappings related to those defined here [2].
1.16. 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 OR 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 ten appendices. WARNING: THE REMAINDER OF THIS SPECIFICATION IS TECHNICALLY DETAILED. IT WILL NOT MAKE SENSE, EXCEPT IN THE CONTEXT OF RFC 822 AND X.400 (1988). DO NOT ATTEMPT TO READ THIS DOCUMENT UNLESS YOU ARE FAMILIAR WITH THESE SPECIFICATIONS. 1.17. Acknowledgements The work in this specification was substantially based on RFC 987 and RFC 1148, which had input from many people, who are credited in the respective documents. A number of comments from people on RFC 1148 lead to RFC 1327. In particular, there were comments and suggestions from: Maurice Abraham (HP); Harald Alvestrand (Sintef); Peter Cowen (X-Tel); Jim Craigie (JNT); Ella Gardner (MITRE); Christian Huitema (Inria); Erik Huizer (SURFnet); Neil Jones (DEC); Ignacio Martinez (IRIS); Julian Onions (X-Tel); Simon Poole (SWITCH); Clive Roberts (Data General); Pete Vanderbilt (SUN); Alan Young (Concurrent). RFC 1327 has been widely adopted, and a review team was formed. This comprised of: Urs Eppenberger (SWITCH)(Chair); Claudio Allocchio (INFN); Harald Alvestrand (UNINETT); Dave Crocker (Brandenburg); Ned Freed (Innosoft); Erik Huizer (SURFnet); Steve Kille (Isode); Peter Sylvester (GC Tech).
Harald Alvestrand also supplied the tables mapping DSN status codes with X.400 codes. Ned Freed defined parts of the File Transfer Body Part mapping. Comment and input has also been received from: Bengt Ackzell (Generic Systems); Samir Albadine (Transpac); Mark Boyes (DEC); Larry Campbell (Boston Software Works); Jacqui Caren (Cray); Allan Cargille (MCI); Kevin Carrosso (Innosoft); Charlie Combs (OIW); Jim Craigie (Net- Tel); Eamon Doyle (Isocor); Efifion Edem (SITA); Jyrki Heikkinen (ICL); Edward Hibbert (DCL); Jeroun Houttin (Terena); Kevin Jordan (CDS); Paul Kingsnorth (DEC); Carl-Uno Manros (Manros Consulting); Suzan Mendes (Telis); Robert Miles (Softswitch); Roger Mizumorri (Enterprise Solutions Ltd); Keith Moore (University of Tennessee); Ruth Moulton (Net-Tel) Michel Musy (Bull); Kenji Nonaka (NTT): The OIW MHSIG; Tom Oliphant (SWITCH); Julian Onions (NEXOR); Jacob Palme (KTH); Olivier Paridaens (ULB); Mary la Roche (Citicorp); John Setsaas (Maxware); Russell Sharpe (DCL); Patrick Soulier (CCETT); Eftimios Tsigros (Universite Libre de Bruxelles); Sean Turner (IECA); Mark Wahl (Isode); David Wilson (Isode); Bill Wohler (Worldtalk); Alan Young (Isode); Alain Zahm (Telis). Chapter 2 - Service Elements This chapter considers the services offered across a gateway built according to this specification. It gives a view of the functionality provided by such a gateway for communication with users in the opposite domain. This chapter considers service mappings in the context of SINGLE transfers only, and not repeated mappings through multiple gateways. 2.1. The Notion of Service Across a Gateway RFC 822 and X.400 provide a number of services to the end user. This chapter describes the extent to which each service can be supported across an X.400 <-> RFC 822 gateway. The cases considered are single transfers across such a gateway, although the problems of multiple crossings are noted where appropriate. 2.1.1. Origination of Messages When a user originates a message, a number of services are available. Some of these imply actions (e.g., delivery to a recipient), and some are insertion of known data (e.g., specification of a subject field). This chapter describes, for each offered service, to what extent it is supported for a recipient accessed through a gateway. There are three levels of support:
Supported
The corresponding protocol elements map well, and so the service
can be fully provided.
Not Supported
The service cannot be provided, as there is a complete mismatch.
Partial Support
The service can be partially fulfilled.
In the first two cases, the service is simply marked as "Supported"
or "Not Supported". Some explanation may be given if there are
additional implications, or the (non) support is not intuitive. For
partial support, the level of partial support is summarised. Where
partial support is good, this will be described by a phrase such as
"Supported by use of.....". A common case of this is where the
service is mapped onto a non-standard service on the other side of
the gateway, and this would have lead to support if it had been a
standard service. In many cases, this is equivalent to support. For
partial support, an indication of the mechanism is given, in order to
give a feel for the level of support provided. Note that this is not
a replacement for Chapter 5, where the mapping is fully specified.
If a service is described as supported, this implies:
- Semantic correspondence.
- No (significant) loss of information.
- Any actions required by the service element.
An example of a service gaining full support: If an RFC 822
originator specifies a Subject: field, this is considered to be
supported, as an X.400 recipient will get a subject indication.
In many cases, the required action will simply be to make the
information available to the end user. In other cases, actions may
imply generating a delivery report.
All RFC 822 services are supported or partially supported for
origination. The implications of non-supported X.400 services is
described under X.400.
2.1.2. Reception of Messages
For reception, the list of service elements required to support this
mapping is specified. This is really an indication of what a
recipient might expect to see in a message which has been remotely
originated. 2.2. RFC 822 RFC 822 does not explicitly define service elements, as distinct from protocol elements. However, all of the RFC 822 header fields, with the exception of trace, can be regarded as corresponding to implicit RFC 822 service elements. 2.2.1. Origination in RFC 822 A mechanism of mapping, used in several cases, is to map the RFC 822 header into a heading extension in the IPM (InterPersonal Message). This can be regarded as partial support, as it makes the information available to any X.400 implementations which are interested in these services. Communities which require significant RFC 822 interworking are recommended to require that their X.400 User Agents are able to display these heading extensions. Support for the various service elements (headers) is now listed. Date: Supported. From: Supported. For messages where there is also a sender field, the mapping is to "Authorising Users Indication", which has subtly different semantics to the general RFC 822 usage of From:. Sender: Supported. Reply-To: Supported. To: Supported. Cc: Supported. Bcc: Supported. Message-Id: Supported. In-Reply-To: Supported, for a single reference. Where multiple references are given, partial support is given by mapping to "Cross Referencing Indication". This gives similar semantics. References: Supported.
Keywords: Supported by use of a heading extension.
Subject: Supported.
Comments: Supported by use of a heading extension.
Encrypted: Supported by use of a heading extension.
Content-Language: Supported.
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.
MIME introduces a number of headings. Support is defined in RFC
2157.
2.2.2. Reception by RFC 822
This considers reception by an RFC 822 User Agent of a message
originated in an X.400 system and transferred across a gateway. The
following standard services (headers) may be present in such a
message:
Date:
From:
Sender:
Reply-To:
To:
Cc:
Bcc:
Message-Id: In-Reply-To: References: Subject: Content-Type: (See RFC 2157) Content-Transfer-Encoding: (See RFC 2157) MIME-Version: (See RFC 2157) The following services (headers) may be present in the header of a message. These are defined in more detail in Chapter 5 (5.3.4, 5.3.6, 5.3.7): Autoforwarded: Autosubmitted: X400-Content-Identifier: Content-Language: Conversion: Conversion-With-Loss: Delivery-Date: Discarded-X400-IPMS-Extensions: Discarded-X400-MTS-Extensions: DL-Expansion-History: Deferred-Delivery: Expires: Importance: Incomplete-Copy: Latest-Delivery-Time:
Message-Type: Original-Encoded-Information-Types: Originator-Return-Address: Priority: Reply-By: Sensitivity: Supersedes: 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, and registered by publication in this standard. It is intended that co-operating RFC 822 systems may also 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 shall be performed prior to the
gateway.
N/A (MS)
These services are only applicable to Message Store (i.e., a local
service).
Finally, some service elements are not supported. In particular, the
new security services are not mapped onto RFC 822. Unless otherwise
indicated, the behaviour of service elements marked as not supported
will depend on the criticality marking supplied by the user. If the
element is marked as critical for transfer or delivery, a non-
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 (X400-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 IP Message Identification
Non-delivery Notification
Not supported in all cases. Supported where the recipient system
supports NOTARY DSNs. In general all RFC 822 systems will return
error reports by use of IP messages. In other service elements,
this pragmatic result can be treated as effective support of this
service element.
Original Encoded Information Types Indication
Supported as a new RFC 822 header (Original-Encoded-Information-
Types:).
Submission Time Stamp Indication
Supported.
Typed Body
Support is defined in RFC 2157.
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). A MIXER gateway has two conformant options. The
first is not to gateway a message requesting prohibition of
alternate recipient, as this control cannot be guaranteed. This
option supports the service, but may cause unacceptable level of
message rejections. The second is to gateway the message on the
basis that there is no alternate recipient service in RFC 822. RFC
1327 allowed only the second option. If the first option is
shown to be operationally effective, it may be the only option in
future versions of MIXER.
Authorising User's Indication
Supported.
Auto-forwarded Indication
Supported as new RFC 822 header (Auto-Forwarded:).
Basic Physical Rendition
N/A (PDAU).
Blind Copy Recipient Indication
Supported.
Body Part Encryption Indication
Supported by use of a new RFC 822 header (Original-Encoded-
Information-Types:), although in most cases it will not be
possible to map the body part in question.
Content Confidentiality
Not supported.
Content Integrity
Not supported.
Conversion Prohibition
Supported. Operation defined in RFC 2157.
Conversion Prohibition in Case of Loss of Information
Supported. Operation defined in RFC 2157.
Counter Collection
N/A (PDAU).
Counter Collection with Advice
N/A (PDAU).
Cross Referencing Indication
Supported.
Deferred Delivery
N/A (prior). This service shall 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, but may be performed
at the end system if the end system supports NOTARY. Thus, a
notification is sent by the gateway to the originator.
Delivery via Bureaufax Service
N/A (PDAU).
Designation of Recipient by Directory Name
N/A (local).
Disclosure of Other Recipients
Supported by use of a new RFC 822 header (X400-Recipients:). This
is descriptive information for the RFC 822 recipient, and is not
reverse mappable.
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, although RFC 822 supports distribution list functionality.
There is no SMTP leve control to prohibit distribution list
expansion. A MIXER gateway has two conformant options. The
first is not to gateway a message requesting DL expansion
prohibition, as this control cannot be guaranteed. This option
supports the service, but may cause unacceptable level of message
rejections. The second is to gateway the message on the basis that
there is no distribution list service in RFC 822. RFC 1327 allowed
only the second option. If the first option is shown to be
operationally effective, it may be the only option in future
versions of MIXER.
Express Mail Service
N/A (PDAU).
Expiry Date Indication
Supported as new RFC 822 header (Expires:). In general, no
automatic action can be expected.
Explicit Conversion
N/A (prior).
Forwarded IP Message Indication
Supported.
Grade of Delivery Selection
Not Supported. There is no equivalent service in RFC 822.
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 (Content-Language:).
Latest Delivery Designation
Not supported. A new RFC 822 header (Latest-Delivery-Time:) is
provided, which may be used by the recipient for general
information, but will not be acted on by the SMTP infrastrucuture.
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.
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 (Supersedes:).
Ordinary Mail
N/A (PDAU).
Originator Indication
Supported.
Originator Requested Alternate Recipient
Not supported, but is placed as comment next to address (X400-
Recipients:).
Physical Delivery Notification by MHS
N/A (PDAU).
Physical Delivery Notification by PDS
N/A (PDAU).
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 where SMTP and NOTARY are available. In other cases
formally 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 Disallowed 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) is 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. In practice, control of this service 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 service request is 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
Supported where SMTP and NOTARY are used. In principle for other
situations, this is N/A, as non-delivery notifications are not
supported. In practice, most RFC 822 systems will return part or
all of the content along with the IP Message indicating an error
(see Non-delivery Notification).
Sensitivity Indication
Supported as new RFC 822 header (Sensitivity:).
Special Delivery
N/A (PDAU).
Stored Message Deletion
N/A (MS).
Stored Message Fetching
N/A (MS).
Stored Message Listing
N/A (MS).
Stored Message Summary
N/A (MS).
Subject Indication
Supported.
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.
Auto-Submitted Indication
Supported
2.3.2. Reception by X.400
2.3.2.1. Standard Mandatory Services
The following standard IPM mandatory user facilities are required for
reception of RFC 822 originated mail by an X.400 UA.
Content Type Indication
Delivery Time Stamp Indication
IP Message Identification
Message Identification
Non-delivery Notification
Original Encoded Information Types Indication
Submission Time Stamp Indication
Typed Body
2.3.2.2. Standard Optional Services The following standard IPM optional user facilities are required for reception of RFC 822 originated mail by an X.400 UA. Authorising User's Indication Blind Copy Recipient Indication Cross Referencing Indication Originator Indication Primary and Copy Recipients Indication Replying IP Message Indication Subject Indication 2.3.2.3. New Services A new X.400 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.
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