RFC 1148: Mapping between X.400(1988) / ISO 10021 and RFC 822
- S.E. Kille
Experimental
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 Kille [Page 1]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 2]
RFC 1148 Mapping X.400(88) and 822 March 1990 / 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. Kille [Page 3]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 4]
RFC 1148 Mapping X.400(88) and 822 March 1990 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. Kille [Page 5]
RFC 1148 Mapping X.400(88) and 822 March 1990 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. Kille [Page 6]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 7]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 8]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 9]
RFC 1148 Mapping X.400(88) and 822 March 1990 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. Kille [Page 10]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 11]
RFC 1148 Mapping X.400(88) and 822 March 1990 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. Kille [Page 12]
RFC 1148 Mapping X.400(88) and 822 March 1990 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: Kille [Page 13]
RFC 1148 Mapping X.400(88) and 822 March 1990 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: Kille [Page 14]
RFC 1148 Mapping X.400(88) and 822 March 1990 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. Kille [Page 15]
RFC 1148 Mapping X.400(88) and 822 March 1990 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:). Kille [Page 16]
RFC 1148 Mapping X.400(88) and 822 March 1990 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. Kille [Page 17]
RFC 1148 Mapping X.400(88) and 822 March 1990 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). Kille [Page 18]
RFC 1148 Mapping X.400(88) and 822 March 1990 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:). Kille [Page 19]
RFC 1148 Mapping X.400(88) and 822 March 1990 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:). Kille [Page 20]
RFC 1148 Mapping X.400(88) and 822 March 1990 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, Kille [Page 21]
RFC 1148 Mapping X.400(88) and 822 March 1990 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). Kille [Page 22]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 23]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 24]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 25]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 26]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 27]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 28]
RFC 1148 Mapping X.400(88) and 822 March 1990 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. Kille [Page 29]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 30]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 31]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 "."> Kille [Page 32]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 33]
RFC 1148 Mapping X.400(88) and 822 March 1990 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. Kille [Page 34]
RFC 1148 Mapping X.400(88) and 822 March 1990 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" Kille [Page 35]
RFC 1148 Mapping X.400(88) and 822 March 1990 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: Kille [Page 36]
RFC 1148 Mapping X.400(88) and 822 March 1990 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. Kille [Page 37]
RFC 1148 Mapping X.400(88) and 822 March 1990 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. Kille [Page 38]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 39]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 40]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 41]
RFC 1148 Mapping X.400(88) and 822 March 1990 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. Kille [Page 42]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 43]
RFC 1148 Mapping X.400(88) and 822 March 1990 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 Kille [Page 44]
RFC 1148 Mapping X.400(88) and 822 March 1990 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