This document is obsolete. Please
refer to RFC 2156 and RFC 1327.
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 1.2RFC 822 ............................................... 3 1.3 The need for conversion ............................... 4 1.4 General approach ...................................... 4 1.5 Gatewaying Model ...................................... 5 1.6RFC 987 ............................................... 7 1.7 Aspects not covered ................................... 8 1.8 Subsetting ............................................ 9
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1.9 Document Structure .................................... 9 1.10 Acknowledgements ..................................... 10 2. Service Elements ....................................... 10 2.1 The Notion of Service Across a Gateway ................ 10 2.2RFC 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 5.1RFC 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
This document relates to the CCITT 1988 X.400 Series Recommendations
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/ ISO IEC 10021 on the Message Oriented Text Interchange Service (MOTIS). This ISO/CCITT standard is referred to in this document as "X.400", which is a convenient shorthand. Any reference to the 1984 CCITT Recommendations will be explicit. X.400 defines an Interpersonal Messaging System (IPMS), making use of a store and forward Message Transfer System. This document relates to the IPMS, and not to wider application of X.400. It is expected that X.400 will be implemented very widely.
RFC 822 is the current specification of the messaging standard on the Internet. This standard evolved with the evolution of the network from the ARPANET (created by the Defense Advanced Research Projects Agency) to the Internet, which now involves over 1000 networks and is sponsored by DARPA, NSF, DOE, NASA, and NIH. It specifies an end to end message format. It is used in conjunction with a number of different message transfer protocol environments.
SMTP Networks
On the Internet and other TCP/IP networks, RFC 822 is used in conjunction with two other standards: RFC 821, also known as Simple Mail Transfer Protocol (SMTP) [Postel82a], and RFC 1034 which is a Specification for domains and a distributed name service [Mockapetris87a].
UUCP Networks
UUCP is the UNIX to UNIX CoPy protocol, which is usually used over dialup telephone networks to provide a simple message transfer mechanism. There are some extensions to RFC 822, particularly in the addressing. They use domains which conform to RFC 1034, but not the corresponding domain nameservers [Horton86a].
Csnet
Some portions of Csnet follow the Internet protocols. The dialup portion of Csnet uses the Phonenet protocols as a replacement for RFC 821. This portion uses domains which conform to RFC 1034, but not the corresponding domain nameservers.
Bitnet
Some parts of Bitnet and related networks use RFC 822 related protocols, with EBCDIC encoding.
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JNT Mail Networks
A number of X.25 networks, particularly those associated with the UK Academic Community, use the JNT (Joint Network Team) Mail Protocol, also known as Greybook [Kille84a]. This is used with domains and name service specified by the JNT NRS (Name Registration Scheme) [Larmouth83a].
The mappings specified here are appropriate for all of these networks.
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:
There are a number of basic principles underlying the details of the specification. These principles are goals, and are not achieved in all aspects of the specification.
1. The specification should be pragmatic. There should not be a requirement for complex mappings for "Academic" reasons. Complex mappings should not be required to support trivial additional functionality.
2. Subject to 1), functionality across a gateway should be as high as possible.
3. It is always a bad idea to lose information as a result of any transformation. Hence, it is a bad idea for a gateway
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to discard information in the objects it processes. This includes requested services which cannot be fully mapped.
4. All mail gateways actually operate at exactly one level above the layer on which they conceptually operate. This implies that the gateway must not only be cognisant of the semantics of objects at the gateway level, but also be cognisant of higher level semantics. If meaningful transformation of the objects that the gateway operates on is to occur, then the gateway needs to understand more than the objects themselves.
5. The specification should be reversible. That is, a double transformation should bring you back to where you started.
Management is a local interaction between the user and the IPMS, and is therefore not relevant to gatewaying. The first two services consist of operations to originate and receive the following two objects:
1. IPM (Interpersonal Message). This has two components: a heading, and a body. The body is structured as a sequence of body parts, which may be basic components (e.g., IA5 text, or G3 fax), or IP Messages. The heading consists of fields containing end to end user information, such as subject, primary recipients (To:), and importance.
2. IPN (Inter Personal Notification). A notification about receipt of a given IPM at the UA level.
The Origination service also allows for origination of a probe, which is an object to test whether a given IPM could be correctly received.
The Reception service also allows for receipt of Delivery Reports (DR), which indicate delivery success or failure.
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These IPMS Services utilise the Message Transfer (MT) Abstract Service [CCITT/ISO88c]. The MT Abstract Service provides the following three basic services:
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.
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:
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.
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:
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.
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.
Much of this work is based on the initial specification of RFC 987 and in its addendum RFC 1026. A basic decision is that the mapping will be to the full 1988 version of X.400, and not to a 1984 compatible subset. This is important, to give good support to communities which will utilise full X.400 at an early date. This has
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the following implications:
- This document does not obsolete RFC 987, as it has a different domain of application.
- If a gatewayed message is being transferred to a 1984 system, then RFC 987 should be used. If the X.400 side of the gateway is a 1988 system, then it should be operated in 1984 compatibility mode. There is no advantage and some disadvantage in using the new mapping, and later on applying X.400 downgrading rules. Note that in an environment where RFC 822 is of major importance, it may be desirable for downgrading to consider the case where the message was originated in an RFC 822 system, and mapped according to this specification.
- New features of X.400 can be used to provide a much cleaner mapping than that defined in RFC 987.
Unnecessary change is usually a bad idea. Changes on the RFC 822 side are avoided as far as possible, so that RFC 822 users do not see arbitrary differences between systems conforming to this specification, and those following RFC 987. Changes on the X.400 side are minimised, but are more acceptable, due to the mapping onto a new set of services and protocols.
There have been a number of cases where RFC 987 was used in a manner which was not intended. This section is to make clear some limitations of scope. In particular, this specification does not specify:
- Extensions of RFC 822 to provide access to all X.400 services
- X.400 user interface definition
These are really coupled. To map the X.400 services, this specification defines a number of extensions to RFC 822. As a side effect, these give the 822 user access to SOME X.400 services. However, the aim on the RFC 822 side is to preserve current service, and it is intentional that access is not given to all X.400 services. Thus, it will be a poor choice for X.400 implementors to use RFC 987(88) as an interface - there are too many aspects of X.400 which cannot be accessed through it. If a text interface is desired, a
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specification targeted at X.400, without RFC 822 restrictions, would be more appropriate.
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.
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.
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.
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.
When a user originates a message, a number of services are available. Some of these imply actions (e.g., delivery to a recipient), and some are insertion of known data (e.g., specification of a subject field). This chapter describes, for each offered service, to what extent it is supported for a recipient accessed through a gateway. There are three levels of support:
Supported The corresponding protocol elements map well, and so the service can be fully provided.
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Not Supported The service cannot be provided, as there is a complete mismatch.
Partial Support The service can be partially fulfilled.
In the first two cases, the service is simply marked as "Supported" or "Not Supported". Some explanation may be given if there are additional implications, or the (non) support is not intuitive. For partial support, the level of partial support is summarised. Where partial support is good, this will be described by a phrase such as "Supported by use of.....". A common case of this is where the service is mapped onto a non- standard service on the other side of the gateway, and this would have lead to support if it had been a standard service. In many cases, this is equivalent to support. For partial support, an indication of the mechanism is given, in order to give a feel for the level of support provided. Note that this is not a replacement for Chapter 5, where the mapping is fully specified.
If a service is described as supported, this implies:
- Semantic correspondence.
- No (significant) loss of information.
- Any actions required by the service element.
An example of a service gaining full support: If an RFC 822 originator specifies a Subject: field, this is considered to be supported, as an X.400 recipient will get a subject indication.
All RFC 822 services are supported or partially supported for origination. The implications of non-supported X.400 services is described under X.400.
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.
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
A mechanism of mapping, used in several cases, is to map the RFC 822 header into a heading extension in the IPM (InterPersonal Message). This can be regarded as partial support, as it makes the information available to any X.400 implementations which are interested in these services. Communities which require significant RFC 822 interworking should require that their X.400 User Agents are able to display these heading extensions. Support for the various service elements (headers) is now listed.
Date: Supported.
From: Supported. For messages where there is also a sender field, the mapping is to "Authorising Users Indication", which has subtly different semantics to the general RFC 822 usage of From:.
Sender: Supported.
Reply-To: Supported.
To: Supported.
Cc: Supported.
Bcc: Supported.
Message-Id: Supported.
In-Reply-To: Supported, for a single reference. Where multiple references are given, partial support is given by mapping to "Cross Referencing Indication". This gives similar semantics.
References: Supported.
Keywords: Supported by use of a heading extension.
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Subject: Supported.
Comments: Supported by use of an extra body part.
Encrypted: Supported by use of a heading extension.
Resent-* Supported by use of a heading extension. Note that addresses in these fields are mapped onto text, and so are not accessible to the X.400 user as addresses. In principle, fuller support would be possible by mapping onto a forwarded IP Message, but this is not suggested.
Other Fields In particular X-* fields, and "illegal" fields in common usage (e.g., "Fruit-of-the-day:") are supported by use of heading extensions.
This considers reception by an RFC 822 User Agent of a message originated in an X.400 system and transferred across a gateway. The following standard services (headers) may be present in such a message:
Date:
From:
Sender:
Reply-To:
To:
Cc:
Bcc:
Message-Id:
In-Reply-To:
References:
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Subject:
The following non-standard services (headers) may be present. These are defined in more detail in Chapter 5 (5.3.4, 5.3.6, 5.3.7):
When mapping services from X.400 to RFC 822 which are not supported by RFC 822, new RFC 822 headers are defined. It is intended that these fields will be registered, and that co-operating RFC 822 systems may use them. Where these new fields are used, and no system action is implied, the service can be regarded as being partially supported. Chapter 5 describes how to map X.400 services onto these new headers. Other elements are provided, in part, by the gateway as they cannot be provided by RFC 822.
Some service elements are marked N/A (not applicable). There are five cases, which are marked with different comments:
N/A (local) These elements are only applicable to User Agent / Message Transfer Agent interaction and so they cannot apply to RFC 822 recipients.
N/A (PDAU) These service elements are only applicable where the recipient is reached by use of a Physical Delivery Access Unit (PDAU), and so do not need to be mapped by the gateway.
N/A (reception) These services are only applicable for reception.
N/A (prior) If requested, this service must be performed prior to the gateway.
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N/A (MS) These services are only applicable to Message Store (i.e., a local service).
Finally, some service elements are not supported. In particular, the new security services are not mapped onto RFC 822. Unless otherwise indicated, the behaviour of service elements marked as not supported will depend on the criticality marking supplied by the user. If the element is marked as critical for transfer or delivery, a non- delivery notification will be generated. Otherwise, the service request will be ignored.
These are the mandatory IPM services as listed in Section 19.8 of X.400 / ISO/IEC 10021-1, listed here in the order given. Section 19.8 has cross references to short definitions of each service.
Access management N/A (local).
Content Type Indication Supported by a new RFC 822 header (Content-Type:).
Converted Indication Supported by a new RFC 822 header (X400-Received:).
Delivery Time Stamp Indication N/A (reception).
IP Message Identification Supported.
Message Identification Supported, by use of a new RFC 822 header (X400-MTS-Identifier). This new header is required, as X.400 has two message-ids whereas RFC 822 has only one (see previous service).
Non-delivery Notification Not supported, although in general an RFC 822 system will return error reports by use of IP messages. In other service elements, this pragmatic result can be treated as effective support of this service element.
Original Encoded Information Types Indication Supported as a new RFC 822 header (Original-Encoded-Information-Types:).
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Submission Time Stamp Indication Supported.
Typed Body Some types supported. IA5 is fully supported. ForwardedIPMessage is supported, with some loss of information. Other types get some measure of support, dependent on X.400 facilities for conversion to IA5. This will only be done where content conversion is not prohibited.
This section describes support for the optional (user selectable) IPM services as listed in Section 19.9 of X.400 / ISO/IEC 10021- 1, listed here in the order given. Section 19.9 has cross references to short definitions of each service.
Additional Physical Rendition N/A (PDAU).
Alternate Recipient Allowed Not supported. There is no RFC 822 service equivalent to prohibition of alternate recipient assignment (e.g., an RFC 822 system may freely send an undeliverable message to a local postmaster). Thus, the gateway cannot prevent assignment of alternative recipients on the RFC 822 side. This service really means giving the user control as to whether or not an alternate recipient is allowed. This specification requires transfer of messages to RFC 822 irrespective of this service request, and so this service is not supported.
Authorising User's Indication Supported.
Auto-forwarded Indication Supported as new RFC 822 header (Auto-Forwarded:).
Basic Physical Rendition N/A (PDAU).
Blind Copy Recipient Indication Supported.
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Body Part Encryption Indication Supported by use of a new RFC 822 header (Original-Encoded-Information-Types:), although in most cases it will not be possible to map the body part in question.
Content Confidentiality Not supported.
Content Integrity Not supported.
Conversion Prohibition Supported. In this case, only messages with IA5 body parts, other body parts which contain only IA5, and Forwarded IP Messages (subject recursively to the same restrictions), will be mapped.
Conversion Prohibition in Case of Loss of Information Supported.
Counter Collection N/A (PDAU).
Counter Collection with Advice N/A (PDAU).
Cross Referencing Indication Supported.
Deferred Delivery N/A (prior). This service should always be provided by the MTS prior to the gateway. A new RFC 822 header (Deferred-Delivery:) is provided to transfer information on this service to the recipient.
Deferred Delivery Cancellation N/A (local).
Delivery Notification Supported. This is performed at the gateway. Thus, a notification is sent by the gateway to the originator. If the 822-MTS protocol is JNT Mail, a notification may also be sent by the recipient UA.
Delivery via Bureaufax Service N/A (PDAU).
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Designation of Recipient by Directory Name N/A (local).
Disclosure of Other Recipients Supported by use of a new RFC 822 header (X400-Recipients:). This is descriptive information for the RFC 822 recipient, and is not reverse mappable.
DL Expansion History Indication Supported by use of a new RFC 822 header (DL-Expansion-History:).
DL Expansion Prohibited Distribution List means MTS supported distribution list, in the manner of X.400. This service does not exist in the RFC 822 world. RFC 822 distribution lists should be regarded as an informal redistribution mechanism, beyond the scope of this control. Messages will be sent to RFC 822, irrespective of whether this service is requested. Theoretically therefore, this service is supported, although in practice it may appear that it is not supported.
Express Mail Service N/A (PDAU).
Expiry Date Indication Supported as new RFC 822 header (Expiry-Date:). In general, no automatic action can be expected.
Explicit Conversion N/A (prior).
Forwarded IP Message Indication Supported, with some loss of information. The message is forwarded in an RFC 822 body, and so can only be interpreted visually.
Grade of Delivery Selection N/A (PDAU)
Importance Indication Supported as new RFC 822 header (Importance:).
Incomplete Copy Indication Supported as new RFC 822 header (Incomplete-Copy:).
Language Indication Supported as new RFC 822 header (Language:).
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Latest Delivery Designation Not supported. A new RFC 822 header (Latest-Delivery-Time:) is provided, which may be used by the recipient.
Message Flow Confidentiality Not supported.
Message Origin Authentication N/A (reception).
Message Security Labelling Not supported.
Message Sequence Integrity Not supported.
Multi-Destination Delivery Supported.
Multi-part Body Supported, with some loss of information, in that the structuring cannot be formalised in RFC 822.
Non Receipt Notification Request Not supported.
Non Repudiation of Delivery Not supported.
Non Repudiation of Origin N/A (reception).
Non Repudiation of Submission N/A (local).
Obsoleting Indication Supported as new RFC 822 header (Obsoletes:).
Ordinary Mail N/A (PDAU).
Originator Indication Supported.
Originator Requested Alternate Recipient Not supported, but is placed as comment next to address (X400-Recipients:).
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Physical Delivery Notification by MHS N/A (PDAU).
Physical Delivery Notification by PDS N/A (PDAU).
Physical Forwarding Allowed Supported by use of a comment in a new RFC 822 header (X400-Recipients:), associated with the recipient in question.
Physical Forwarding Prohibited Supported by use of a comment in a new RFC 822 header (X400-Recipients:), associated with the recipient in question.
Prevention of Non-delivery notification Supported, as delivery notifications cannot be generated by RFC 822. In practice, errors will be returned as IP Messages, and so this service may appear not to be supported (see Non-delivery Notification).
Primary and Copy Recipients Indication Supported.
Probe Supported at the gateway (i.e., the gateway services the probe).
Probe Origin Authentication N/A (reception).
Proof of Delivery Not supported.
Proof of Submission N/A (local).
Receipt Notification Request Indication Not supported.
Redirection Allowed by Originator Redirection means MTS supported redirection, in the manner of X.400. This service does not exist in the RFC 822 world. RFC 822 redirection (e.g., aliasing) should be regarded as an informal redirection mechanism, beyond the scope of this control. Messages will be sent to RFC 822, irrespective of whether this service is requested. Theoretically therefore,
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this service is supported, although in practice it may appear that it is not supported.
Registered Mail N/A (PDAU).
Registered Mail to Addressee in Person N/A (PDAU).
Reply Request Indication Supported as comment next to address.
Replying IP Message Indication Supported.
Report Origin Authentication N/A (reception).
Request for Forwarding Address N/A (PDAU).
Requested Delivery Method N/A (local). The services required must be dealt with at submission time. Any such request is made available through the gateway by use of a comment associated with the recipient in question.
Return of Content In principle, this is N/A, as non-delivery notifications are not supported. In practice, most RFC 822 systems will return part or all of the content along with the IP Message indicating an error (see Non-delivery Notification).
Sensitivity Indication Supported as new RFC 822 header (Sensitivity:).
Special Delivery N/A (PDAU).
Stored Message Deletion N/A (MS).
Stored Message Fetching N/A (MS).
Stored Message Listing N/A (MS).
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Stored Message Summary N/A (MS).
Subject Indication Supported.
Undeliverable Mail with Return of Physical Message N/A (PDAU).
Use of Distribution List In principle this applies only to X.400 supported distribution lists (see DL Expansion Prohibited). Theoretically, this service is N/A (prior). In practice, because of informal RFC 822 lists, this service can be regarded as supported.
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.
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.
Structured text is defined according to the Extended Backus Naur Form (EBNF) defined in Section 2 of RFC 822 [Crocker82a]. In the EBNF definitions used in this specification, the syntax rules given in Appendix D of RFC 822 are assumed. When these EBNF tokens are referred to outside an EBNF definition, they are identified by the string "822." appended to the beginning of the string (e.g., 822.addr-spec). Additional syntax rules, to be used throughout this specification, are defined in this chapter.
The EBNF is used in two ways.
1. To describe components of RFC 822 messages (or of 822-MTS components). In this case, the lexical analysis defined in Section 3 of RFC 822 should be used. When these new EBNF tokens are referred to outside an EBNF definition, they are identified by the string "EBNF." appended to the beginning of the string (e.g., EBNF.bilateral-info).
2. To describe the structure of IA5 or ASCII information not in
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an RFC 822 message. In these cases, tokens will either be self delimiting, or be delimited by self delimiting tokens. Comments and LWSP are not used as delimiters.
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].
There is a need to convert between ASCII text, and some of the types defined in ASN.1 [CCITT/ISO88d]. For each case, an EBNF syntax
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definition is given, for use in all of this specification, which leads to a mapping between ASN.1, and an EBNF construct.
All EBNF syntax definitions of ASN.1 types are in lower case, whereas ASN.1 types are referred to with the first letter in upper case. Except as noted, all mappings are symmetrical.
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:
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.
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.
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
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.
The 822.3DIGIT in EBNF.ps-encoded-char must have range 0-127, and is interpreted in decimal as the corresponding ASCII character. Special encodings are given for: at sign (@), percent (%), exclamation mark/bang (!), double quote ("), underscore (_), left bracket ((), and right bracket ()). These characters, with the exception of round brackets, are not included in PrintableString, but are common in RFC 822 addresses. The abbreviations will ease specification of RFC 822 addresses from an X.400 system. These special encodings should be mapped in a case insensitive manner, but always be generated in lower case.
A reversible mapping between PrintableString and ASCII can now be defined. The reversibility means that some values of printable string (containing round braces) cannot be generated from ASCII. Therefore, this mapping must only be used in cases where the printable strings may only be derived from ASCII (and will therefore have a restricted domain). For example, in this specification, it is
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only applied to a Domain defined attribute which will have been generated by use of this specification and a value such as "(" would not be possible.
To encode ASCII as PrintableString, the EBNF.ps-encoded syntax is used, with all EBNF.ps-restricted-char mapped directly. All other 822.CHAR are encoded as EBNF.ps-encoded-char.
To encode PrintableString as ASCII, parse PrintableString as EBNF.ps-encoded, and then reverse the previous mapping. If the PrintableString cannot be parsed, then the mapping is being applied in to an inappropriate value, and an error should be given to the procedure doing the mapping. In some cases, it may be preferable to pass the printable string through unaltered.
Some examples are now given. Note the arrows which indicate asymmetrical mappings:
Addressing is probably the trickiest problem of an X.400 <-> RFC 822 gateway. Therefore it is given a separate chapter. This chapter, as a side effect, also defines a textual representation of an X.400 O/R Address.
Initially, we consider an address in the (human) mail user sense of "what is typed at the mailsystem to reference a mail user". A basic RFC 822 address is defined by the EBNF EBNF.822-address:
822-address = [ route ] addr-spec
In an 822-MTS protocol, the originator and each recipient should be considered to be defined by such a construct. In an RFC 822 header, the EBNF.822-address is encapsulated in the 822.address syntax rule, and there may also be associated comments. None of this extra information has any semantics, other than to the end user.
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The basic X.400 O/R Address, used by the MTS for routing, is defined by MTS.ORAddress. In IPMS, the MTS.ORAddress is encapsulated within IPMS.ORDescriptor.
It can be seen that RFC 822 822.address must be mapped with IPMS.ORDescriptor, and that RFC 822 EBNF.822-address must be mapped with MTS.ORAddress.
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.
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
The following keys identify different EBNF encodings, which are associated with the ASCII representation of MTS.ORAddress.
Key Encoding
P printablestring N numericstring T teletex-string
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P/T teletex-and-or-ps I labelled-integer X presentation-address
The BNF for presentation-address is taken from the specification "A String Encoding of Presentation Address" [Kille89a].
In most cases, the EBNF encoding maps directly to the ASN.1 encoding of the attribute. There are a few exceptions. In cases where an attribute can be encoded as either a PrintableString or NumericString (Country, ADMD, PRMD), either form should be mapped into the BNF. When generating ASN.1, the NumericString encoding should be used if the string contains only digits.
There are a number of cases where the P/T (teletex-and-or-ps) representation is used. Where the key maps to a single attribute, this choice is reflected in the encoding of the attribute (attributes 10-21). For most of the 1984 attributes and common name, there is a printablestring and a teletex variant. This pair of attributes is mapped onto the single component here. This will give a clean mapping for the common cases where only one form of the name is used.
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.
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.
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!
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.
Ideally, the mapping specified would be entirely symmetrical and global, to enable addresses to be referred to transparently in the remote system, with the choice of gateway being left to the Message Transfer Service. There are two fundamental reasons why this is not possible:
1. The syntaxes are sufficiently different to make this awkward.
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2. In the general case, there would not be the necessary administrative co-operation between the X.400 and RFC 822 worlds, which would be needed for this to work.
Therefore, an asymmetrical mapping is defined, which can be symmetrical where there is appropriate administrative control.
The std-or-address syntax is used to encode O/R Address information in the 822.local-part of EBNF.822-address. Further O/R Address information may be associated with the 822.domain component. This cannot be used in the general case, basically due to character set problems, and lack of order in X.400 O/R Addresses. The only way to encode the full PrintableString character set in a domain is by use of the 822.domain-ref syntax (i.e., 822.atom). This is likely to cause problems on many systems. The effective character set of domains is in practice reduced from the RFC 822 set, by restrictions imposed by domain conventions and policy.
A generic 822.address consists of a 822.local-part and a sequence of 822.domains (e.g., <@domain1,@domain2:user@domain3>). All except the 822.domain associated with the 822.local-part (domain3 in this case) should be considered to specify routing within the RFC 822 world, and will not be interpreted by the gateway (although they may have identified the gateway from within the RFC 822 world).
This form of source routing is now discouraged in the Internet (Host Requirements, page 58 [Braden89a]).
The 822.domain associated with the 822.local-part may also identify the gateway from within the RFC 822 world. This final 822.domain may be used to determine some number of O/R Address attributes. The following O/R Address attributes are considered as a hierarchy, and may be specified by the domain. They are (in order of hierarchy):
Country, ADMD, PRMD, Organisation, Organisational Unit
There may be multiple Organisational Units.
Associations may be defined between domain specifications, and some set of attributes. This association proceeds hierarchically. For example, if a domain implies ADMD, it also implies country. Subdomains under this are associated according to the O/R Address hierarchy. For example:
=> "AC.UK" might be associated with C="GB", ADMD="GOLD 400", PRMD="UK.AC"
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then domain "R-D.Salford.AC.UK" maps with C="GB", ADMD="GOLD 400", PRMD="UK.AC", O="Salford", OU="R-D"
There are three basic reasons why a domain/attribute mapping might be maintained, as opposed to using simply subdomains:
1. As a shorthand to avoid redundant X.400 information. In particular, there will often be only one ADMD per country, and so it does not need to be given explicitly.
2. To deal with cases where attribute values do not fit the syntax:
domain-syntax = alphanum [ *alphanumhyphen alphanum ] alphanum = <ALPHA or DIGIT> alphanumhyphen = <ALPHA or DIGIT or HYPHEN>
Although RFC 822 allows for a more general syntax, this restricted syntax is chosen as it is the one chosen by the various domain service administrations.
3. To deal with missing elements in the hierarchy. A domain may be associated with an omitted attribute in conjunction with several present ones. When performing the algorithmic insertion of components lower in the hierarchy, the omitted value should be skipped. For example, if "HNE.EGM" is associated with "C=TC", "ADMD=ECQ", "PRMD=HNE", and omitted organisation, then "ZI.HNE.EGM" is mapped with "C=TC", "ADMD=ECQ", "PRMD=HNE", "OU=ZI". It should be noted that attributes may have null values, and that this is treated separately from omitted attributes (whilst it would be bad practice to treat these two cases differently, they must be allowed for).
This set of mappings need only be known by the gateways relaying between the RFC 822 world, and the O/R Address space associated with the mapping in question. However, it is desirable (for the optimal mapping of third party addresses) for all gateways to know these mappings. A format for the exchange of this information is defined in Appendix F.
The remaining attributes are encoded on the LHS, using the EBNF.std- or-address syntax. For example:
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.
In some cases, the encoding defined above may be reversed, to give a "natural" encoding of genuine RFC 822 addresses. This depends largely on the allocation of appropriate management domains.
The general case is mapped by use of domain defined attributes. A Domain defined type "RFC-822" is defined. The associated attribute value is an ASCII string encoded according to Section 3.3.3 of this specification. The interpretation of the ASCII string depends on the context of the gateway.
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1. In the context of RFC 822, and RFC 1034 [Crocker82a, Mockapetris87a], the string can be used directly.
2. In the context of the JNT Mail protocol, and the NRS [Kille84a, Larmouth83a], the string should be interpreted according to Mailgroup Note 15 [Kille84b].
3. In the context of UUCP based systems, the string should be interpreted as defined in [Horton86a].
Other O/R Address attributes will be used to identify a context in which the O/R Address will be interpreted. This might be a Management Domain, or some part of a Management Domain which identifies a gateway MTA. For example:
C = "GB" ADMD = "GOLD 400" PRMD = "UK.AC" O = "UCL" OU = "CS" "RFC-822" = "Jimmy(a)WIDGET-LABS.CO.UK"
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.
In most cases, ordering of O/R Address components is not significant for the mappings specified. However, Organisational Units (printable string and teletex forms) and Domain Defined Attributes are specified as SEQUENCE in MTS.ORAddress, and so their order may be significant. This specification needs to take account of this:
1. To allow consistent mapping into the domain hierarchy
2. To ensure preservation of order over multiple mappings.
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There are three places where an order must be specified:
1. The text encoding (std-or-address) of MTS.ORAddress as used in the local-part of an RFC 822 address. An order is needed for those components which may have multiple values (Organisational Unit, and Domain Defined Attributes). When generating an 822.std-or-address, components of a given type shall be in hierarchical order with the most significant component on the RHS. If there is an Organisation Attribute, it shall be to the right of any Organisational Unit attributes. These requirements are for the following reasons:
- Alignment to the hierarchy of other components in RFC 822 addresses (thus, Organisational Units will appear in the same order, whether encoded on the RHS or LHS). Note the differences of JNT Mail as described in Appendix B.
- To ensure that gateways generate consistent addresses. This is both to help end users, and to generate identical message ids.
Further, it is recommended that all other attributes are generated according to this ordering, so that all attributes so encoded follow a consistent hierarchy.
There will be some cases where an X.400 O/R address of this encoding will be generated by an end user from external information. The ordering of attributes may be inverted or mixed. For this reason, the following heuristics may be applied:
- If there is an Organisation attribute to the left of any Org Unit attribute, assume that the hierarchy is inverted.
- If an inversion of the Org Unit hierarchy generates a valid address, when the preferred order does not, assume that the hierarchy is inverted.
2. For the Organisational Units (OU) in MTS.ORAddress, the first OU in the SEQUENCE is the most significant, as specified in X.400.
3. For the Domain Defined Attributes in MTS.ORAddress, the
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First Domain Defined Attribute in the SEQUENCE is the most significant.
Note that although this ordering is mandatory for this mapping, there are NO implications on ordering significance within X.400, where this is a Management Domain issue.
The mapping should proceed as follows, by first assuming case 1).
STAGE I.
1. If the 822-address is not of the form:
local-part "@" domain
Go to stage II.
NOTE:It may be appropriate to reduce a source route address to this form by removal of all bar the last domain. In terms of the design intentions of RFC 822, this would be an incorrect action. However, in most real cases, it will do the "right" thing and provide a better service to the end user. This is a reflection on the excessive and inappropriate use of source routing in RFC 822 based systems. Either approach, or the intermediate approach of stripping only domain references which reference the local gateway are conformant to this specification.
2. Attempt to parse EBNF.domain as:
*( domain-syntax "." ) known-domain
Where EBNF.known-domain is the longest possible match in a list of supported mappings (see Appendix F). If this fails, and the EBNF.domain does not explicitly identify the local gateway, go to stage II. If it succeeds, allocate the attributes associated with EBNF.known-domain, and systematically allocate the attributes implied by each
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EBNF.domain-syntax component. If the domain explicitly identifies the gateway, allocate no attributes.
3. If the local-part contains any characters not in PrintableString, go to stage II.
4. If the 822.local-part uses the 822.quoted-string encoding, remove this quoting. Parse the (unquoted) 822.local-part according to the EBNF EBNF.std-or-address. If this parse fails, parse the local-part according to the EBNF EBNF.encoded-pn. The result is a set of type/value pairs. If the values generated conflict with those derived in step 2 (e.g., a duplicated country attribute), the domain should be assumed to be an RFC 987 gateway. In this case, take only the LHS derived attributes. Otherwise add LHS and RHS derived attributes together.
5. Associate the EBNF.attribute-value syntax (determined from the identified type) with each value, and check that it conforms. If not, go to stage II.
6. Ensure that the set of attributes conforms both to the MTS.ORAddress specification and to the restrictions on this set given in X.400. If not go to stage II.
This will only be reached if the RFC 822 EBNF.822-address is not a valid X.400 encoding. If the address is an 822-MTS recipient address, it must be rejected, as there is a need to interpret such an address in X.400. For the 822-MTS return address, and any addresses in the RFC 822 header, they should now be encoded as RFC 822 addresses in an X.400 O/R Name:
1. Convert the EBNF.822-address to PrintableString, as specified in Chapter 3.
2. The "RFC-822" domain defined attribute should be generated from this string.
3. Build the rest of the O/R Address in the local Management Domain agreed manner, so that the O/R Address will receive a correct global interpretation.
Note that the domain defined attribute value has a maximum length
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of MTS.ub-domain-defined-attribute-value-length (128). If this is exceeded by a mapping at the MTS level, then the gateway should reject the message in question. If this occurs at the IPMS level, then the action should depend on the policy being taken, which is discussed in Section 5.1.3.
2. "Genuine" X.400 addresses. This may include symmetrically encoded RFC 822 addresses.
When a MTS Recipient O/R Address is interpreted, gatewaying will be selected if there a single "RFC-822" domain defined attribute present. In this case, use mapping A. For other O/R Addresses which:
1. Contain the special attribute.
AND
2. Identifies the local gateway or any other known gateway with the other attributes.
Use mapping A. In other cases, use mapping B.
NOTE: A pragmatic approach would be to assume that any O/R Address with the special domain defined attribute identifies an RFC 822 address. This will usually work correctly, but is in principle not correct.
Mapping A
1. Map the domain defined attribute value to ASCII, as defined in Chapter 3.
Mapping B
This will be used for X.400 addresses which do not use the explicit RFC 822 encoding.
1. For all string encoded attributes, remove any leading or trailing spaces, and replace adjacent spaces with a single space.
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2. Noting the hierarchy specified in 4.3.1, determine the maximum set of attributes which have an associated domain specification. If no match is found, allocate the domain as the domain specification of the local gateway, and go to step 4.
3. Following the 4.3.1 hierarchy and noting any omitted components implied by the mapping tables (see Appendix F), if each successive component exists, and conforms to the syntax EBNF.domain-syntax (as defined in 4.3.1), allocate the next subdomain. At least one attribute of the X.400 address should not be mapped onto subdomain, as 822.local-part cannot be null.
4. If the remaining components are personal-name components, conforming to the restrictions of 4.2.1, then EBNF.encoded- pn should be derived to form 822.local-part. In other cases the remaining components should simply be encoded as a 822.local-part using the EBNF.std-or-address syntax. If necessary, the 822.quoted-string encoding should be used.
If the derived 822.local-part can only be encoded by use of 822.quoted-string, then use of the mapping defined in [Kille89b] may be appropriate. Use of this mapping is discouraged.
The mappings defined are symmetrical and reversible across a single gateway. The symmetry is particularly useful in cases of (mail exploder type) distribution list expansion. For example, an X.400 user sends to a list on an RFC 822 system which he belongs to. The received message will have the originator and any 3rd party X.400 O/R Addresses in correct format (rather than doubly encoded). In cases (X.400 or RFC 822) where there is common agreement on gateway identification, then this will apply to multiple gateways.
When a message traverses multiple gateways, the mapping will always be reversible, in that a reply can be generated which will correctly reverse the path. In many cases, the mapping will also be symmetrical, which will appear clean to the end user. For example, if countries "AB" and "XY" have RFC 822 networks, but are interconnected by X.400, the following may happen: The originator specifies:
Joe.Soap@Widget.PTT.XY
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This is routed to a gateway, which generates:
C = "XY" ADMD = "PTT" PRMD = "Griddle MHS Providers" Organisation = "Widget Corporation" Surname = "Soap" Given Name = "Joe"
This is then routed to another gateway where the mapping is reversed to give:
Joe.Soap@Widget.PTT.XY
Here, use of the gateway is transparent.
Mappings will only be symmetrical where mapping tables are defined. In other cases, the reversibility is more important, due to the (far too frequent) cases where RFC 822 and X.400 services are partitioned.
The syntax may be used to source route. THIS IS STRONGLY DISCOURAGED. For example:
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:
Directory Names are an optional part of O/R Name, along with O/R Address. The RFC 822 addresses are mapped onto the O/R Address component. As there is no functional mapping for the Directory Name on the RFC 822 side, a textual mapping should be used. There is no requirement for reversibility in terms of the goals of this specification. There may be some loss of functionality in terms of third party recipients where only a directory name is given, but this seems preferable to the significant extra complexity of adding a full mapping for Directory Names.
From the 822-MTS Originator, use the basic ORAddress mapping, to generate MTS.PerMessageSubmissionFields.originator-name (MTS.ORName), without a DirectoryName.
For recipients, the following settings should be made for each component of MTS.PerRecipientMessageSubmissionFields.
recipient-name This should be derived from the 822-MTS recipient by the basic ORAddress mapping.
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originator-report-request This should be set according to content return policy, as discussed in Section 5.2.
explicit-conversion This optional component should be omitted, as this service is not needed.
extensions The default value (no extensions) should be used.
The basic functionality is to generate the 822-MTS originator and recipients. There is information present on the X.400 side, which cannot be mapped into analogous 822-MTS services. For this reason, new RFC 822 fields are added for the MTS Originator and Recipients. The information discarded at the 822-MTS level should be present in these fields. There may also be the need to generate a delivery report.
Use the basic ORAddress mapping, to generate the 822-MTS originator (return address) from MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName). If MTS.ORName.directory-name is present, it should be discarded.
The 822-MTS recipient is conceptually generated from MTS.OtherMessageDeliveryFields.this-recipient-name. This is done by taking MTS.OtherMessageDeliveryFields.this-recipient-name, and generating an 822-MTS recipient according to the basic ORAddress mapping, discarding MTS.ORName.directory-name if present. However, if this model was followed exactly, there would be no possibility to have multiple 822-MTS recipients on a single message. This is unacceptable, and so layering is violated. The mapping needs to use the MTA level information, and map each value of MTA.PerRecipientMessageTransferFields.recipient-name, where the responsibility bit is set, onto an 822-MTS recipient.
Not all per-recipient information can be passed at the 822-MTS level. For this reason, two new RFC 822 headers are created, in order to carry this information to the RFC 822 recipient. These fields are "X400-Originator:" and "X400-Recipients:".
The "X400-Originator:" field should be set to the same value as the
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822-MTS originator. In addition, if MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName) contains MTS.ORName.directory-name then this Directory Name should be represented in an 822.comment.
Recipient names, taken from each value of MTS.OtherMessageDeliveryFields.this-recipient-name and MTS.OtherMessageDeliveryFields.other-recipient-names should be made available to the RFC 822 user by use of the "X400-Recipients:" field. By taking the recipients at the MTS level, disclosure of recipients will be dealt with correctly. If any MTS.ORName.directory-name is present, it should be represented in an 822.comment. If MTS.OtherMessageDeliveryFields.orignally-intended-recipient-name is present, then it should be represented in an associated 822.comment, starting with the string "Originally Intended Recipient".
In addition, the following per-recipient services from MTS.OtherMessageDeliveryFields.extensions should be represented in comments if they are used. None of these services can be provided on RFC 822 networks, and so in general these will be informative strings associated with other MTS recipients. In some cases, string values are defined. For the remainder, the string value may be chosen by the implementor. If the parameter has a default value, then no comment should be inserted.
If MTA.PerRecipientMessageTransferFields.per-recipient-indicators requires a positive delivery notification, this should be generated by the gateway. Supplementary Information should be set to indicate that the report is gateway generated.
A mapping from 822.msg-id to MTS.MTSIdentifier is defined. The reverse mapping is not needed, as MTS.MTSIdentifier is always mapped onto new RFC 822 fields. The value of MTS.MTSIdentifier.local-part will facilitate correlation of gateway errors.
To map from 822.msg-id, apply the standard mapping to 822.msg-id, in order to generate an MTS.ORAddress. The Country, ADMD, and PRMD components of this should be used to generate MTS.MTSIdentifier.global-domain-identifier. MTS.MTSIdentifier.local-identifier should be set to the 822.msg-id, including the braces "<" and ">". If this string is longer than MTS.ub-local-id-length (32), then it should be truncated to this length.
The reverse mapping is not used in this specification. It would be applicable where MTS.MTSIdentifier.local-identifier is of syntax 822.msg-id, and it algorithmically identifies MTS.MTSIdentifier.
All RFC 822 addresses are assumed to use the 822.mailbox syntax. This should include all 822.comments associated with the lexical tokens of the 822.mailbox. In the IPMS O/R Names are encoded as MTS.ORName. This is used within the IPMS.ORDescriptor, IPMS.RecipientSpecifier, and IPMS.IPMIdentifier. An asymmetrical mapping is defined between these components.
To derive IPMS.ORDescriptor from an RFC 822 address.
1. Take the address, and extract an EBNF.822-address. This can be derived trivially from either the 822.addr-spec or 822.route-addr syntax. This is mapped to MTS.ORName as described above, and used as IMPS.ORDescriptor.formal-name.
2. A string should be built consisting of (if present):
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- The 822.phrase component if the 822.address is an 822.phrase 822.route-addr construct.
- Any 822.comments, in order, retaining the parentheses.
This string should then be encoded into T.61 us a human oriented mapping (as described in Chapter 3). If the string is not null, it should be assigned to IPMS.ORDescriptor.free-form-name.
3. IPMS.ORDescriptor.telephone-number should be omitted.
If IPMS.ORDescriptor is being used in IPMS.RecipientSpecifier, IPMS.RecipientSpecifier.reply-request and IPMS.RecipientSpecifier.notification-requests should be set to default values (none and false).
If the 822.group construct is present, any included 822.mailbox should be encoded as above to generate a separate IPMS.ORDescriptor. The 822.group should be mapped to T.61, and a IPMS.ORDescriptor with only an free-form-name component built from it.
Mapping from IPMS.ORDescriptor to RFC 822 address. In the basic case, where IPMS.ORDescriptor.formal-name is present, proceed as follows.
1. Encode IPMS.ORDescriptor.formal-name (MTS.ORName) as EBNF.822-address.
2a. If IPMS.ORDescriptor.free-form-name is present, convert it to ASCII (Chapter 3), and use this as the 822.phrase component of 822.mailbox using the 822.phrase 822.route-addr construct.
2b. If IPMS.ORDescriptor.free-form-name is absent. If EBNF.822-address is parsed as 822.addr-spec use this as the encoding of 822.mailbox. If EBNF.822-address is parsed as 822.route 822.addr-spec, then a 822.phrase taken from 822.local-part should be added.
3. If IPMS.ORDescriptor.telephone-number is present, this should be placed in an 822.comment, with the string "Tel ". The normal international form of number should be used. For example:
(Tel +44-1-387-7050)
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4. If IPMS.ORDescriptor.formal-name.directory-name is present, then a text representation should be placed in a trailing 822.comment.
5. If IPMS.RecipientSpecifier.report-request has any non- default values, then an 822.comment "(Receipt Notification Requested)", and/or "(Non Receipt Notification Requested)", and/or "(IPM Return Requested)" should be appended to the address. The effort of correlating P1 and P2 information is too great to justify the gateway sending Receipt Notifications.
6. If IPMS.RecipientSpecifier.reply-request is True, an 822.comment "(Reply requested)" should be appended to the address.
If IPMS.ORDescriptor.formal-name is absent, IPMS.ORDescriptor.free- form-name should be converted to ASCII, and used as 822.phrase within the RFC 822 822.group syntax. For example:
There is a need to map both ways between 822.msg-id and IPMS.IPMIdentifier. This allows for X.400 Receipt Notifications, Replies, and Cross References to reference an RFC 822 Message ID, which is preferable to a gateway generated ID. A reversible and symmetrical mapping is defined. This allows for good things to happen when messages pass multiple times across the X.400/RFC 822 boundary.
An important issue with messages identifiers is mapping to the exact form, as many systems use these ids as uninterpreted keys. The use of table driven mappings is not always symmetrical, particularly in the light of alternative domain names, and alternative management domains. For this reason, a purely algorithmic mapping is used. A mapping which is simpler than that for addresses can be used for two reasons:
- There is no major requirement to make message IDs "natural"
- There is no issue about being able to reply to message IDs. (For addresses, creating a return path which works is more important than being symmetrical).
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The mapping works by defining a way in which message IDs generated on one side of the gateway can be represented on the other side in a systematic manner. The mapping is defined so that the possibility of clashes is is low enough to be treated as impossible.
IPMS.IPMIdentifier.user is omitted. The IPMS.IPMIdentifier.user- relative-identifier is set to a printable string encoding of the 822.msg-id with the angle braces ("<" and ">") removed.
4.7.3.2. IPMS.IPMIdentifier represented in RFC 822
The 822.domain of 822.msg-id is set to the value "MHS". The 822.local-part of 822.msg-id is built as:
[ printablestring ] "*" [ std-or-address ]
with EBNF.printablestring being the IPMS.IPMIdentifier.user- relative-identifier, and std-or-address being an encoding of the IPMS.IPMIdentifier.user. If necessary, the 822.quoted-string encoding is used. For example:
and the 822.domain is "MHS", then this ID was X.400 generated. If EBNF.printablestring is present, the value is assigned to IPMS.IPMIdentifier.user-relative-identifier. If EBNF.std-or-address is present, the O/R Address components derived from it are used to set IPMS.IPMIdentifier.user.
Otherwise, this is an RFC 822 generated ID. In this case, set IPMS.IPMIdentifier.user-relative-identifier to a printable string encoding of the 822.msg-id without the angle braces.
If IPMS.IPMIdentifier.user is absent, and IPMS.IPMIdentifier.user- relative-identifier mapped to ASCII and angle braces added parses as 822.msg-id, then this is an RFC 822 generated ID.
Otherwise, the ID is X.400 generated. Use the
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IPMS.IPMIdentifier.user to generate an EBNF.std-or-address form string. Build the 822.local-part of the 822.msg-id with the syntax:
[ printablestring ] "*" [ std-or-address ]
The printablestring is taken from IPMS.IPMIdentifier.user-relative- identifier. Use 822.quoted-string if necessary. The 822.msg-id is generated with this 822.local-part, and "MHS" as the 822.domain.
In "Reply-To:" and "References:", the encoding 822.phrase may be used as an alternative to 822.msg-id. To map from 822.phrase to IPMS.IPMIdentifier, assign IPMS.IPMIdentifier.user-relative- identifier to the phrase. When mapping from IPMS.IPMIdentifier for "Reply-To:" and "References:", if IPMS.IPMIdentifier.user is absent and IPMS.IPMIdentifier.user-relative-identifier does not parse as 822.msg-id, generate an 822.phrase rather than adding the domain MHS.
The mapping proposed here is different to that used in RFC 987, as the RFC 987 mapping lead to changed message IDs in many cases. Fixing the problems is preferable to retaining backwards compatibility. An implementation of this standard is encouraged to recognise message IDs generated by RFC 987.
Chapter 5 -- Detailed Mappings
This chapter gives detailed mappings for the functions outlined in Chapters 1 and 2. It makes extensive use of the notations and mappings defined in Chapters 3 and 4.
A single IP Message is generated. The RFC 822 headers are used to generate the IPMS.Heading. The IP Message will have one IA5 IPMS.BodyPart containing the RFC 822 message body.
Some RFC 822 fields cannot be mapped onto a standard IPM Heading field, and so an extended field is defined in Section 5.1.2. This is then used for fields which cannot be mapped onto existing services.
The message is submitted to the MTS, and the services required can be defined by specifying MTS.MessageSubmissionEnvelope. A few parameters of the MTA Abstract service are also specified, which are
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not in principle available to the MTS User. Use of these services allows RFC 822 MTA level parameters to be carried in the analogous X.400 service elements. The advantages of this mapping far outweigh the layering violation.
The Object Identifier id-rfc-822-field is defined in Appendix D.
To encode any RFC 822 Header using this extension, the RFC822Field should be set to the 822.field omitting the trailing CRLF (e.g., "Fruit-Of-The-Day: Kiwi Fruit"). Structured fields should be unfolded. There should be no space before the ":". The reverse mapping builds the RFC 822 field in a straightforward manner.
The IPM (IPMS Service Request) is generated according to the rules of this section. The IPMS.IPM.body usually consists of one IPMS.BodyPart of type IPMS.IA5TextbodyPart with IPMS.IA5TextBodyPart.parameters.repertoire set to the default (ia5) which contains the body of the RFC 822 message. The exception is where there is a "Comments:" field in the RFC 822 header.
If no specific 1988 features are used, the IPM generated should be encoded as content type 2. Otherwise, it should be encoded as content type 22. The latter will always be the case if extension heading fields are generated.
When generating the IPM, the issue of upper bounds must be considered. At the MTS and MTA level, this specification is strict about enforcing upper bounds. Three options are available at the IPM level. Use of any of these options conforms to this standard.
1. Ignore upper bounds, and generate messages in the natural manner. This assumes that if any truncation is done, it will happen at the recipient UA. This will maximise transfer of information, but may break some recipient UAs.
2. Reject any inbound message which would cause a message
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violating constraints to be generated. This will be robust, but may prevent useful communication.
3. Truncate fields to the upper bounds specified in X.400. This will prevent problems with UAs which enforce upper bounds, but will sometimes discard useful information.
These choices have different advantages and disadvantages, and the choice will depend on the exact application of the gateway.
The rest of this section concerns IPMS.IPM.heading (IPMS.Heading). The only mandatory component of IPMS.Heading is the IPMS.Heading.this-IPM (IPMS.IPMIdentifier). A default should be generated by the gateway. With the exception of "Received:", the values of multiple fields should be merged (e.g., If there are two "To:" fields, then the mailboxes of both should be used). Information should be generated from the standard RFC 822 Headers as follows:
Date: Ignore (Handled at MTS level)
Received: Ignore (Handled at MTA level)
Message-Id: Mapped to IPMS.Heading.this-IPM. For these, and all other fields containing 822.msg-id the mappings of Chapter 4 are used for each 822.msg-id.
From: If Sender: is present, this is mapped to IPMS.Heading.authorizing-users. If not, it is mapped to IPMS.Heading.originator. For this, and other components containing addresses, the mappings of Chapter 4 are used for each address.
Sender: Mapped to IPMS.Heading.originator.
Reply-To: Mapped to IPMS.Heading.reply-recipients.
To: Mapped to IPMS.Heading.primary-recipients
Cc: Mapped to IPMS.Heading.copy-recipients.
Bcc: Mapped to IPMS.Heading.blind-copy-recipients.
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In-Reply-To: If there is one value, it is mapped to IPMS.Heading.replied-to-IPM, using the 822.phrase or 822.msg-id mapping as appropriate. If there are several values, they are mapped to IPMS.Heading.related-IPMs, along with any values from a "References:" field.
References: Mapped to IPMS.Heading.related-IPMs.
Keywords: Mapped onto a heading extension.
Subject: Mapped to IPMS.Heading.subject. The field-body uses the human oriented mapping referenced in Chapter 3 from ASCII to T.61.
Comments: Generate an IPMS.BodyPart of type IPMS.IA5TextbodyPart with IPMS.IA5TextBodyPart.parameters.repertoire set to the default (ia5), containing the value of the fields, preceded by the string "Comments: ". This body part should precede the other one.
Encrypted: Mapped onto a heading extension.
Resent-* Mapped onto a heading extension.
Note that it would be possible to use a ForwardedIPMessage for these fields, but the semantics are (arguably) slightly different, and it is probably not worth the effort.
Other Fields In particular X-* fields, and "illegal" fields in common usage (e.g., "Fruit-of-the-day:") are mapped onto a heading extension, unless covered by another section or appendix of this specification. The same treatment should be applied to RFC 822 fields where the content of the field does not conform to RFC 822 (e.g., a Date: field with unparsable syntax).
The MTS.MessageSubmissionEnvelope comprises MTS.PerMessageSubmissionFields, and
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MTS.PerRecipientMessageSubmissionFields. The mandatory parameters should be defaulted as follows.
MTS.PerMessageSubmissionFields.originator-name This is always generated from 822-MTS, as defined in Chapter 4.
MTS.PerMessageSubmissionFields.content-type Set to the value implied by the encoding of the IPM (2 or 22).
MTS.PerRecipientMessageSubmissionFields.recipient-name These will always be supplied from 822-MTS, as defined in Chapter 4.
Optional components should be left out, and default components defaulted, with two exceptions. For MTS.PerMessageSubmissionFields.per-message-indicators, the following settings should be made:
- Alternate recipient should be allowed, as it seems desirable to maximise the opportunity for (reliable) delivery.
- Content return request should be set according to the issues discussed in Section 5.2.
MTS.PerMessageSubmissionFields.original-encoded-information-types should be made a set of one element BuiltInEncodedInformationTypes.ia5-text.
The MTS.PerMessageSubmissionFields.content-correlator should be encoded as IA5String, and contain the Subject:, Message-ID:, Date:, and To: fields (if present). This should include the strings "Subject:", "Date:", "To:", "Message-ID:", and appropriate folding. This should be truncated to MTS.ub-content-correlator-length (512) characters. In addition, if there is a "Subject:" field, the MTS.PerMessageSubmissionFields.content-identifier, should be set to a printable string representation of the contents of it, truncated to MTS.ub-content-id-length (16). Both are used, due to the much larger upper bound of the content correlator, and that the content id is available in X.400(1984).
- So that the submission date can be generated from the 822.Date.
- To prevent loss of trace information.
- To prevent RFC 822/X.400 looping caused by distribution lists or redirects.
The following mappings are defined.
Message-Id: If this is present, the MTA.PerMessageTransferFields.message-identifier should be generated from it, using the mappings described in Chapter 4.
Date: This is used to set the first component of MTA.PerMessageTransferFields.trace-information (MTA.TraceInformationElement). The 822-MTS originator should be mapped into an MTS.ORAddress, and used to derive MTA.TraceInformationElement.global-domain-identifier. The optional components of MTA.TraceInformationElement.domain-supplied-information are omitted, and the mandatory components are set as follows:
MTA.DomainSuppliedInformation.arrival-time This is set to the date derived from Date:
MTA.DomainSuppliedInformation.routing-action Set to relayed.
The first element of MTA.PerMessageTransferFields.internal-trace-information should be generated in an analogous manner, although this may later be dropped (see the procedures for "Received:").
Received: All RFC 822 trace is used to derive MTA.PerMessageTransferFields.trace-information and MTA.PerMessageTransferFields.internal-trace-information. Processing of Received: lines should follow processing of Date:, and should be done from the the bottom to the top of the RFC 822 header (i.e., in chronological order). If other trace elements are processed (Via:, X400-Received:), care should be taken to keep the relative ordering correct. The
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initial element of MTA.PerMessageTransferFields.trace-information will be generated already (from Date:).
Consider the Received: field in question. If the "by" part of the received is present, use it to derive an MTS.GlobalDomainIdentifier. If this is different from the one in the last element of MTA.PerMessageTransferFields.trace-information (MTA.TraceInformationElement.global-domain-identifier) create a new MTA.TraceInformationElement, and optionally remove MTA.PerMessageTransferFields.internal-trace-information. This removal should be done in cases where the message is being transferred to another MD where there is no bilateral agreement to preserve internal trace beyond the local MD. The trace creation is as for internal trace described below, except that no MTA field is needed.
Then add a new element (MTA.InternalTraceInformationElement) to MTA.PerMessageTransferFields.internal-trace-information, creating this if needed. This shall be done, even if inter-MD trace is created. The MTA.InternalTraceInformationElement.global-domain-identifier should be set to the value derived. The MTA.InternalTraceInformationElement.mta-supplied-information (MTA.MTASuppliedInformation) should be set as follows:
MTA.MTASuppliedInformation.arrival-time Derived from the date of the Received: line
MTA.MTASuppliedInformation.routing-action Set to relayed
The MTA.InternalTraceInformationElement.mta-name should be taken from the "by" component of the "Received:" field, truncated to MTS.ub-mta-name-length (32). For example:
Received: from computer-science.nottingham.ac.uk by vs6.Cs.Ucl.AC.UK via Janet with NIFTP id aa03794; 28 Mar 89 16:38 GMT
Generates the string:
vs6.Cs.Ucl.AC.UK
Note that before transferring the message to some ADMDs, additional trace stripping may be required, as the implied path through multiple
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MDs would violate ADMD policy.
Two extended fields must be mapped, in order to prevent looping. "DL-Expansion-History:" is mapped to MTA.PerMessageTransferFields.extensions.dl-expansion-history. "Redirection-History:" is mapped to MTA.PerRecipientMessageTransferFields.extensions.redirection-history.
This specification defines a number of new fields for Reports, Notifications and IP Messages in Section 5.3. As this specification only aims to preserve existing services, a gateway conforming to this specification does not need to map these fields to X.400, with the exception of "DL-Expansion-History" and "Redirection-History" described in the previous section. However, it is usually desirable and beneficial to do so, particularly to facilitate support of a message traversing multiple gateways. These mappings may be onto MTA, MTS, or IPMS services.
It is not clear how widely supported the X.400 return of contents service will be. Experience with X.400(1984) suggests that support of this service may not be universal. As this service is expected in the RFC 822 world, two approaches are specified. The choice will depend on the use of X.400 return of contents withing the X.400 community being serviced by the gateway.
In environments where return of contents is widely supported, content return can be requested as a service. The content return service can then be passed back to the end (RFC 822) user in a straightforward manner.
In environments where return of contents is not widely supported, a gateway must make special provision to handle return of contents. For every message passing from RFC 822 -> X.400, content return request will not be requested, and report request always will be. When the delivery report comes back, the gateway can note that the message has been delivered to the recipient(s) in question. If a non-delivery report is received, a meaningful report (containing some or all of the original message) can be sent to the 822-MTS originator. If no report is received for a recipient, a (timeout) failure notice should be sent to the 822-MTS originator. The gateway may retransmit the X.400 message if it wishes. When this approach is taken, routing must be set up so that error reports are returned through the same MTA. This approach may be difficult to use in conjunction with some routing strategies.
A single RFC 822 message is generated from the incoming IP Message, Report, or IP Notification. All IPMS.BodyParts are mapped onto a single RFC 822 body. Other services are mapped onto RFC 822 header fields. Where there is no appropriate existing field, new fields are defined for IPMS, MTS and MTA services.
The gateway mechanisms will correspond to MTS Delivery. As with submission, there are aspects where the MTA (transfer) services are also used. In particular, there is an optimisation to allow for multiple 822-MTS recipients.
An RFC 822 Service requires to have a number of mandatory fields in the RFC 822 Header. Some 822-MTS services mandate specification of an 822-MTS Originator. Even in cases where this is optional, it is usually desirable to specify a value. The following defaults are defined, which should be used if the mappings specified do not derive a value:
822-MTS Originator If this is not generated by the mapping (e.g., for a Delivery Report), a value pointing at a gateway administrator should be assigned.
Date: A value will always be generated
From:If this is not generated by the mapping, it should be assigned equal to the 822-MTS Originator. If this is gateway generated, an appropriate 822.phrase should be added.
At least one recipient field If no recipient fields are generated, a field "To: list:;", should be added.
This will ensure minimal RFC 822 compliance. When generating RFC 822 headers, folding should be used in an appropriate manner.
MTS.EncodedInformationTypes is mapped onto EBNF.encoded-info. MTS.EncodedInformationTypes.non-basic-parameters is ignored. Built in types are mapped onto fixed strings (compatible with X.400(1984) and RFC 987), and other types are mapped onto EBNF.object-identifier.
Consider that an IPM has to be mapped to RFC 822. The IPMS.IPM comprises an IPMS.IPM.heading and IPMS.IPM.body. The heading is considered first. Some EBNF for new fields is defined:
The mappings and actions for the IPMS.Heading is now specified for each element. Addresses, and Message Identifiers are mapped according to Chapter 4. Other mappings are explained, or are straightforward (algorithmic).
IPMS.Heading.this-IPM Mapped to "Message-ID:".
IPMS.Heading.originator If IPMS.Heading.authorizing-users is present this is mapped to Sender:, if not to "From:".
IPMS.Heading.authorizing-users Mapped to "From:".
IPMS.Heading.primary-recipients Mapped to "To:".
IPMS.Heading.copy-recipients Mapped to "Cc:".
IPMS.Heading.blind-copy-recipients Mapped to "Bcc:".
IPMS.Heading.replied-to-ipm Mapped to "In-Reply-To:".
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IPMS.Heading.obsoleted-IPMs Mapped to the extended RFC 822 field "Obsoletes:"
IPMS.Heading.related-IPMs Mapped to "References:".
IPMS.Heading.subject Mapped to "Subject:". The contents are converted to ASCII (as defined in Chapter 3). Any CRLF are not mapped, but are used as points at which the subject field must be folded.
IPMS.Heading.expiry-time Mapped to the extended RFC 822 field "Expiry-Date:".
IPMS.Heading.reply-time Mapped to the extended RFC 822 field "Reply-By:".
IPMS.Heading.reply-recipients Mapped to "Reply-To:".
IPMS.Heading.importance Mapped to the extended RFC 822 field "Importance:".
IPMS.Heading.sensitivity Mapped to the extended RFC 822 field "Sensitivity:".
IPMS.Heading.autoforwarded Mapped to the extended RFC 822 field "Autoforwarded:".
The standard extensions (Annex H of X.420 / ISO 10021-7) are mapped as follows:
incomplete-copy Mapped to the extended RFC 822 field "Incomplete-Copy:".
language Mapped to the extended RFC 822 field "Language:", filling in the two letter code. If possible, the language-description should be filled in with a human readable description of the language.
If the RFC 822 extended header is found, this should be mapped onto an RFC 822 header, as described in Section 5.1.2.
If a non-standard extension is found, it should be discarded, unless the gateway understands the extension and can perform an appropriate mapping onto an RFC 822 header field. If extensions are discarded,
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the list should be indicated in the extended RFC 822 field "Discarded-X400-IPMS-Extensions:".
The IPMS.Body is mapped into the RFC 822 message body. Each IPMS.BodyPart is converted to ASCII as follows:
IPMS.IA5Text The mapping is straightforward (see Chapter 3).
IPMS.MessageBodyPart The X.400 -> RFC 822 mapping should be recursively applied, to generate an RFC 822 Message. If present, the IPMS.MessageBodyPart.parameters.delivery-envelope should be used for the MTS Abstract Service Mappings. If present, the IPMS.MessageBodyPart.parameters.delivery-time should be mapped to the extended RFC 822 field "Delivery-Date:".
Other If other body parts can be mapped to IA5, either by use of mappings defined in X.408 [CCITT88a], or by other reasonable mappings, this should be done unless content conversion is prohibited.
If some or all of the body parts cannot be converted there are three options. All of these conform to this standard. A different choice may be made for the case where no body part can be converted:
1. The first option is to reject the message, and send a non- delivery notification. This must always be done if conversion is prohibited.
2. The second option is to map a missing body part to something of the style:
*********************************
There was a foobar here
The widget gateway ate it
*********************************
This will allow some useful information to be transferred. As the recipient is a human (IPMS), then suitable action should be available.
3. Finally both can be done. In this case, the supplementary information in the (positive) Delivery Report should make
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clear that something was sent on to the recipient with substantial loss of information.
Where there is more than one IPMS.BodyPart, the mapping defined by Rose and Stefferud in [Rose85a], should be used to map the separate IPMS.BodyParts in the single RFC 822 message body. If this is done, a "Message-Type:" field with value "Multiple part" should be added, which will indicate to a receiving gateway that the message may be unfolded according to RFC 934.
For backwards compatibility with RFC 987, the following procedures should also be followed. If there are two IA5 body parts, and the first starts with the string "RFC-822-Headers:" as the first line, then the remainder of this body part should be appended to the RFC 822 header.
A message is generated, with the following fields:
From: Set to the MTS.MessageDeliveryEnvelope.other- fields.originator-name.
To: Set to the IPMS.IPN.ipm-originator.
Subject: Set to something of the form "X.400 Inter-Personal Receipt Notification".
Message-Type: Set to "InterPersonal Notification"
References: Set to IPMS.IPN.subject-ipm
The following EBNF is defined for the body of the Message. This format is defined to ensure that all information from an interpersonal notification is available to the end user in a uniform manner.
"was received at" receipt-time <CRLF> <CRLF> "This notification was generated" acknowledgement-mode <CRLF> "The following extra information was given:" <CRLF> ipn-suppl <CRLF>
The mappings for elements of the common fields of IPMS.IPN (IPMS.CommonFields) onto this structure and the message header are:
subject-ipm Mapped to "References:"
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ipm-originator Mapped to "To:".
ipm-preferred-recipient Mapped to EBNF.preferred-recipient
conversion-eits Mapped to EBNF.encoded-info in EBNF.ipn-extra-information
The mappings for elements of IPMS.IPN.non-receipt-fields (IPMS.NonReceiptFields) are:
non-receipt-reason Used to select between EBNF.ipn-discarded and EBNF.ipn-auto-forwarded
discard-reason Mapped to EBNF.discard-reason
auto-forward-comment Mapped to EBNF.auto-comment
returned-ipm If present, the second option of EBNF.ipn-content-return should be chosen, and an RFC 822 mapping of the message included. Otherwise the first option should be chosen.
The mappings for elements of IPMS.IPN.receipt-fields (IPMS.ReceiptFields) are:
receipt-time Mapped to EBNF.receipt-time
acknowledgement-mode Mapped to EBNF.acknowledgement-mode
suppl-receipt-info Mapped to EBNF.ipn-suppl
An example notification is:
From: Steve Kille <steve@cs.ucl.ac.uk> To: Julian Onions <jpo@computer-science.nottingham.ac.uk> Subject: X400 Inter-personal Receipt Notification Message-Type: InterPersonal Notification References: <1229.614418325@UK.AC.NOTT.CS> Date: Wed, 21 Jun 89 08:45:25 +0100
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Your message to: Steve Kille <steve@cs.ucl.ac.uk> was automatically forwarded. The following comment was made: Sent on to a random destination
The following information types were converted: g3fax
This section describes the MTS mappings for User Messages (IPM and IPN). This mapping is defined by specifying the mapping of MTS.MessageDeliveryEnvelope. The following extensions to RFC 822 are defined to support this mapping:
The mappings for each element of MTS.MessageDeliveryEnvelope can now be considered.
MTS.MessageDeliveryEnvelope.message-delivery-identifier Mapped to the extended RFC 822 field "X400-MTS-Identifier:".
MTS.MessageDeliveryEnvelope.message-delivery-time Discarded, as this time will be represented in an appropriate trace element.
The mappings for elements of MTS.MessageDeliveryEnvelope.other-fields (MTS.OtherMessageDeliveryFields) are:
content-type Mapped to the extended RFC 822 field "X400-Content-Type:". The string "P2" is for backwards compatibility with RFC 987. If the content type is 22, then a labelled-integer encoding should be used.
originator-name Mapped to the 822-MTS originator, and to the extended RFC 822 field "X400-Originator:". This is described in Section 4.6.2.
original-encoded-information-types Mapped to the extended RFC 822 field "Original-Encoded-Information-Types:".
priority Mapped to the extended RFC 822 field "Priority:".
delivery-flags If the conversion-prohibited bit is set, add an extended RFC 822 field "Conversion:".
this-recipient-name and other-recipient-names These fields are used together, to generate the extended RFC 822 field "X400-Recipients:". Note that the latter will only be present if disclosure of recipients is allowed.
originally-intended-recipient-name Mapped to a comment associated with the recipient in
converted-encoded-information-types Discarded, as it will always be IA5 only.
message-submission-time Mapped to Date:.
content-identifier Mapped to the extended RFC 822 field "Content-Identifier:".
If any extensions (MTS.MessageDeliveryEnvelope.other-fields.extensions) are present, and they are marked as critical for transfer or delivery, then the message should be rejected. The extensions (MTS.MessageDeliveryEnvelope.other-fields.extensions) are mapped as follows.
conversion-with-loss-prohibited If set to MTS.ConversionWithLossProhibited.conversion-with-loss-prohibited, then add the extended RFC 822 field "Conversion-With-Loss:".
requested-delivery-method Mapped to the extended RFC 822 field "Requested-Delivery-Method:".
originator-return-address Mapped to the extended RFC 822 field "Originator-Return-Address:".
These elements are only appropriate for physical delivery. They are represented as comments in the "X400-Recipients:" field, as described in Section 4.6.2.2.
These elements imply use of security services not available in the RFC 822 environment. If they are marked as critical for transfer or delivery, then the message should be rejected. Otherwise they should be discarded.
redirection-history Each element is mapped to an extended RFC 822 field "Redirection-History:". They should be ordered in the message header, so that the most recent redirection comes first (same order as trace).
dl-expansion-history Each element is mapped to the extended RFC 822 field "DL-Expansion-History:". They should be ordered in the message header, so that the most recent expansion comes first (same order as trace).
If any MTS (or MTA) Extensions not specified in X.400 are present, and they are marked as critical for transfer or delivery, then the message should be rejected. If they are not so marked, they can safely be discarded. The list of discarded fields should be indicated in the extended header "Discarded-X400-MTS-Extensions:".
There are some mappings at the MTA Abstract Service level which are done for IPM and IPN. These can be derived from MTA.MessageTransferEnvelope. The reasons for the mappings at this level, and the violation of layering are:
- Allowing for multiple recipients to share a single RFC 822 message.
- Making the X.400 trace information available on the RFC 822 side.
- Making any information on deferred delivery available.
The 822-MTS recipients should be calculated from the full list of X.400 recipients. This is all of the members of MTA.MessageTransferEnvelope.per-recipient-fields being passed through the gateway, where the responsibility bit is set. In some cases, a different RFC 822 message would be calculated for each recipient. If this is due to differing service requests for each recipient, then a different message should be generated.
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If it is due only to the request for non-disclosure of recipients, then the "X400-Recipients:" field should be omitted, and only one message sent.
The following EBNF is defined for extended RFC 822 headers:
If MTA.PerMessageTransferFields.deferred-delivery-time is present, use it to generate a Deferred-Delivery: field. For some reason, X.400 does not make this information available at the MTS level on delivery. X.400 profiles, and in particular the CEN/CENELEC profile for X.400(1984) [Systems85a], specify that this element must be supported at the first MTA. If it is not, the function may optionally be implemented by the gateway: that is, the gateway should hold the message until the time specified in the protocol element. Thus, it is expected that the value of this element will often be in the past. For this reason, the extended RFC 822 field is primarily for information.
Merge MTA.PerMessageTransferFields.trace-information, and MTA.PerMessageTransferFields.internal-trace-information to produce a single ordered trace list. If Internal trace from other management domains has not been stripped, this may require complex interleaving. Use this to generate a sequence of "X400-Received:" fields. The only difference between external trace and internal trace will be the
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extra MTA information in internal trace elements.
When generating an RFC 822 message all trace fields (X400- Received and Received) should be at the beginning of the header, before any other fields. Trace should be in chronological order, with the most recent element at the front of the message. A simple example trace (external) is:
X400-Received: by /PRMD=UK.AC/ADMD=Gold 400/C=GB/ ; Relayed ; Tue, 20 Jun 89 19:25:11 +0100
A more complex example (internal):
X400-Received: by mta UK.AC.UCL.CS in /PRMD=UK.AC/ADMD=Gold 400/C=GB/ ; deferred until Tue, 20 Jun 89 14:24:22 +0100 ; converted (undefined, g3fax) ";" attempted /ADMD=Foo/C=GB/ ; Relayed, Expanded, Redirected ; Tue, 20 Jun 89 19:25:11 +0100
Delivery reports are mapped at the MTS service level. This means that only reports destined for the MTS user will be mapped. Some additional services are also taken from the MTA service.
A Delivery Report service will be represented as MTS.ReportDeliveryEnvelope, which comprises of per-report-fields (MTS.PerReportDeliveryFields) and per-recipient-fields.
A message should be generated with the following fields:
From: An administrator at the gateway system. This is also the 822-MTS originator.
To: A mapping of the MTA.ReportTransferEnvelope.report-destination-name. This is also the 822-MTS recipient.
Message-Type: Set to "Delivery Report".
Subject: Something of the form "X.400 Delivery Report".
The format of the body of the message is defined to ensure that all
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information is conveyed to the RFC 822 user in a consistent manner. This gives a summary of critical information, and then a full listing of all parameters:
dr-recip-failure = "Your message was not delivered to:" mailbox <CRLF> "for the following reason:" *word
dr-extra-information = "-----------------------------------------------" <CRLF> <CRLF> "The following information is derived from the Report" <CRLF> "It may be useful for problem diagnosis:" <CRLF> <CRLF> drc-field-list
The format is defined as a fixed definition. The only exception is that the EBNF.drc-fields should follow RFC 822 folding rules.
The elements of MTS.ReportDeliveryEnvelope.per-report-fields are mapped as follows onto extended RFC 822 fields:
subject-submission-identifier Mapped to EBNF.drc-field (Subject-Submission-Identifier)
content-identifier Mapped to EBNF.drc-field (Content-Identifier)
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content-type Mapped to EBNF.drc-field (Content-Type)
original-encoded-information-types Mapped to EBNF.drc-field (Encoded-Info)
The extensions from MTS.ReportDeliveryEnvelope.per-report-fields.extensions are mapped as follows:
originator-and-DL-expansion-history Mapped to EBNF.drc-field (Originator-and-DL-Expansion- History)
reporting-DL-name Mapped to EBNF.drc-field (Reporting-DL-Name)
content-correlator Mapped to EBNF.content-correlator, provided that the encoding is IA5String (this should always be the case). This is used in EBNF.dr-summary and EBNF.drc-field-list. In the former, LWSP may be added, in order to improve the layout of the message.
These security parameters should not be present. If they are, they should be discarded in preference to discarding the whole report.
For each element of MTS.ReportDeliveryEnvelope.per-recipient-fields, a value of EBNF.dr-recipient, and an EBNF.drc-field (Recipient-Info) should be generated. The components are mapped as follows.
actual-recipient-name Used to generate the first EBNF.mailbox and EBNF.std-or in EBNF.recipient-info. Both RFC 822 and X.400 forms are given, as there may be a problem in the mapping tables. It also generates the EBNF.mailbox in EBNF.dr-recip-success or EBNF.dr-recip-failure.
report If it is MTS.Report.delivery, then set EBNF.dr-recipient to EBNF.dr-recip-success, and similarly set EBNF.report-type, filling in EBNF.drc-success. If it is a failure, set EBNF.dr-recipient to EBNF.dr-recip-failure, making a human
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interpretation of the reason and diagnostic codes, and including any supplementary information. EBNF.drc-failure should be filled in systematically.
converted-encoded-information-types Set EBNF.drc-field ("converted eits")
originally-intended-recipient Set the second ("originally intended recipient") mailbox
and
std-or in EBNF.drc-field.
supplementary-info Set EBNF.drc-field ("supplementary info"), and include this information in EBNF.dr-recip-failure.
redirection-history Set EBNF.drc-field ("redirection history")
physical-forwarding-address Set ENBF.drc-field ("physical forwarding address")
recipient-certificate Discard
proof-of-delivery Discard
Any unknown extensions should be discarded, irrespective of criticality.
The original message should be included in the delivery port. The original message will usually be available at the gateway, as discussed in Section 5.2.
The single 822-MTS recipient is constructed from MTA.ReportTransferEnvelope.report-destination-name, using the mappings of Chapter 4. Unlike with a user message, this information is not available at the MTS level.
The following additional mappings should be made:
MTA.ReportTransferEnvelope.report-destination-name This should be used to generate the To: field.
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MTA.ReportTransferEnvelope.identifier Mapped to the extended RFC 822 field "X400-MTS-Identifier:". It may also be used to derive a "Message-Id:" field.
MTA.ReportTransferEnvelope.trace-information and
MTA.ReportTransferEnvelope.internal-trace-information Mapped onto the extended RFC 822 field "X400-Received:", as described in Section 5.3.7. The first element should also be used to generate the "Date:" field, and the EBNF.failure-point.
MTA.PerRecipientReportTransferFields.last-trace-information Mapped to EBNF.recipient-info (last trace) MTA.PerReportTransferFields.subject-intermediate-trace-information Mapped to EBNF.drc-field (subject-Intermediate-Trace-Information). These fields should be ordered so that the most recent trace element comes first.
This is an example, of a moderately complex report.
From: The Postmaster <postmaster@cs.ucl.ac.uk> To: jpo@computer-science.nottingham.ac.uk Subject: X.400 Delivery Report Message-Type: Delivery Report Date: Wed, 21 Jun 89 08:45:25 +0100 X400-MTS-Identifier: /PRMD=UK.AC/ADMD=Gold 400/C=GB/;13412345235
This report relates to your message: Date: Wed, 21 Jun 89 06:15:43 +0000 Message-ID: <8907140715.aa09015@CS.Nott.AC.UK> Subject: Now it's the fine tuning .... ! To: Piete Brooks (Postmaster) <pb@computer-lab.cambridge.ac.uk>
of Wed, 21 Jun 89 06:15:43 +0000
It was generated by mta PK in /PRMD=UK/ADMD=DBP/C=DE/ at Wed, 21 Jun 89 08:45:25 +0100
It was later converted to RFC 822 by: Mail-Gateway@oxbridge.ac.uk at Wed, 21 Jun 89 08:45:26 +0100
Your message was not delivered to: bad-user@nowhere for the following reason: Rendition problem with punctuation (Umlaut failure)
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-----------------------------------------------
The following information is derived from the Report It may be useful for problem diagnosis:
Subject-Submission-Identifier: [/PRMD=UK.AC/ADMD=Gold 400/C=GB/;148996] Content-Identifier: X.400 Delivery Report Content-Type: P2-1988 (22) Original-Encoded-Information-Types: ia5 Content-Correlator: Date: Wed, 21 Jun 89 06:15:43 +0000 Message-ID: <8907140715.aa09015@CS.Nott.AC.UK> Subject: Now it's the fine tuning .... ! To: Piete Brooks (Postmaster) <pb@computer-lab.cambridge.ac.uk> Recipient-Info: bad-user@nowhere, /S=bad-user/PRMD=nowhere/ADMD=DBP/C=DE/ ; FAILURE reason Physical-Rendition-Not-Performed (3) ; diagnostic Punctuation-Symbol-Loss (23) ; supplementary info Umlaut failure
The Original Message follows:
Subject: Now it's the fine tuning .... ! Date: Wed, 21 Jun 89 06:15:43 +0000 From: Julian Onions <jpo@computer-science.nottingham.ac.uk> To: Piete Brooks (Postmaster) <pb@computer-lab.cambridge.ac.uk> Cc: bad-user@nowhere Message-ID: <8907140715.aa09015@CS.Nott.AC.UK>
This is an MTS internal issue. Any probe should be serviced by the gateway, as there is no equivalent RFC 822 functionality. The value of the reply is dependent on whether the gateway could service an MTS Message with the values specified in the probe. The reply should make use of MTS.SupplementaryInformation to indicate that the probe was serviced by the gateway.
This Appendix is specific to the JNT Mail Protocol. It describes specific changes in the context of this protocol.
1. Introduction
There are five aspects of a gateway which are JNT Mail Specific. These are each given a section of this appendix.
2. Domain Ordering
When interpreting and generating domains, the UK NRS domain ordering must be used.
3. Acknowledge-To:
This field has no direct functional equivalent in X.400. However, it can be supported to an extent, and can be used to improve X.400 support.
If an Acknowledge-To: field is present when going from JNT Mail to X.400, MTS.PerRecipientSubmissionFields.originator-request- report.report shall be set for each recipient. If there is more that one address in the Acknowledge-To: field, or if the one address is not equivalent to the 822-MTS return address, then:
1. Acknowledgement(s) should be generated by the gateway. The text of these acknowledgements should indicate that they are generated by the gateway.
2. The Acknowledge-To: field should also be passed as an extension heading.
When going from X.400 to JNT Mail, in cases where MTA.PerRecipientMessageTransferFields.per-recipient-indicators.
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originator-report is set, the copy of the message to that recipient should have an Acknowledge-To: field containing the MTS.OtherMessageDeliveryFields.originator-name. No special treatment should be given when MTA.PerRecipientMessageTransferFields.per- recipient-indicators. originating-MTA-report is set. No attempt should be made to map Receipt notification requests onto Acknowledge-To:, as no association can be guaranteed between IPMS and MTS level addressing information.
4. Trace
JNT Mail trace uses the Via: syntax. When going from JNT Mail to X.400, a mapping similar to that for Received: is used. No MTS.GlobalDomainIdentifier of the site making the trace can be derived from the Via:, so a value for the gateway should be used. The trace text, including the "Via:", should be unfolded, truncated to MTS.ub-mta-name-length (32), and mapped to MTA.InternalTraceInformationElement.mta-name. There is no JNT Mail specific mapping for the reverse direction.
5. Timezone specification
The extended syntax of zone defined in the JNT Mail Protocol should be used in the mapping of UTCTime defined in Chapter 3.
6. Lack of 822-MTS originator specification
In JNT Mail the default mapping of the MTS.OtherMessageDeliveryFields.originator-name is to the Sender: field. This can cause a problem when going from X.400 to JNT Mail if the mapping of IPMS.Heading has already generated a Sender: field. To overcome this, new extended JNT Mail field is defined. This is chosen to align with the JNT recommendation for interworking with full RFC 822 systems [Kille84b].
original-sender = "Original-Sender" ":" mailbox
If an IPM has no IPMS.Heading.authorising-users component and IPMS.Heading.originator.formal-name is different from MTS.OtherMessageDeliveryFields.originator-name, map MTS.OtherMessageDeliveryFields.originator-name, onto the Sender: field.
If an IPM has a IPMS.Heading.authorising-users component, and IPMS.Heading.originator.formal-name is different from MTS.OtherMessageDeliveryFields.originator-name, MTS.OtherMessageDeliveryFields.originator-name should be mapped onto the Sender: field, and IPMS.Heading.originator mapped onto the
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Original-Sender: field.
In other cases the MTS.OtherMessageDeliveryFields.originator-name, is already correctly represented.
Gatewaying of UUCP and X.400 is handled by first gatewaying the UUCP address into RFC 822 syntax (using RFC 976) and then gatewaying the resulting RFC 822 address into X.400. For example, an X.400 address:
Country US Organisation Xerox Personal Name John Smith
(assuming gate is a UUCP-Internet gateway and gatehost.COM is an Internet-X.400 gateway) or
inthop!gate!Xerox.COM!John.Smith
(assuming that Xerox.COM and /C=US/O=Xerox/ are equivalent.)
In the other direction, a UUCP address Smith@ATT.COM, integrated into 822, would be handled as any other 822 address. A non-integrated address such as inthop!dest!user might be handled through a pair of gateways:
Country US ADMD ATT PRMD Internet Organisation GateOrg RFC-822 inthop!dest!user@gatehost.COM
or through a single X.400 to UUCP gateway:
Country US ADMD ATT PRMD UUCP Organisation GateOrg RFC-822 inthop!dest!user
ipn-receipt = "Your message to:" preferred-recipient <CRLF> "was received at" receipt-time <CRLF> <CRLF> "This notification was generated" acknowledgement-mode <CRLF> "The following extra information was given:" <CRLF> ipn-suppl <CRLF>
ipn-non-receipt "Your message to:"
preferred-recipient <CRLF> ipn-reason
ipn-reason = ipn-discarded / ipn-auto-forwarded
ipn-discarded = "was discarded for the following reason:" discard-reason <CRLF>
ipn-auto-forwarded = "was automatically forwarded." <CRLF> [ "The following comment was made:"
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auto-comment ]
ipn-extra-information = "The following information types were converted:" encoded-info
ipn-content-return = "The Original Message is not available" / "The Original Message follows:" <CRLF> <CRLF> message
There is a need to specify the association between the domain and X.400 namespaces described in Chapter 4. The use of this association leads to a better service on both sides of the gateway, and so defining mappings and distributing them in the form defined in this appendix is strongly encouraged.
This syntax defined is initially in table form, but the syntax is defined in a manner which makes it suitable for use with domain nameservices (such as the Internet Domain nameservers or the UK NRS). The mapping is not symmetric, and so a separate table is specified for each direction. If multiple matches are possible, the longest possible match should be used.
First, an address syntax is defined, which is compatible with the syntax used for 822.domains. It is intended that this syntax may be used in conjunction with systems which support this form of name.
To allow the mapping of null attributes to be represented, the pseudo-value "@" (not a printable string character) is used to indicate omission of a level in the hierarchy. This is distinct from the form including the element with no value, although a correct X.400 implementation will interpret both in the same manner.
This syntax is not intended to be handled by users.
The first example illustrates quoting of a ".", and the second omission of the ADMD level.
Various further restrictions are placed on the usage of dmn-or- address:
1. Only C, ADMD, PRMD, O, and OU may be used.
2. There must be a strict ordering of all components, with the most significant components on the RHS.
3. No components may be omitted from the hierarchy, although the hierarchy may terminate at any level. If the mapping is to an omitted component, the "@" syntax is used.
For domain -> X.400:
domain-syntax "#" dmn-or-address "#"
Note that the trailing "#" is used for clarity, as the dmn-or- address syntax can lead to values with trailing blanks. Lines staring with "#" are comments.
[Braden89a] Braden, R., Editor, "Requirements for Internet Hosts -- Application and Support", RFC 1123, USC/Information Sciences Institute, October 1989.
[CCITT88a] CCITT, "CCITT Recommendations X.408", Message Handling Systems: Encoded Information Type Conversion Rules, CCITT, December
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1988.
[CCITT/ISO88a] CCITT/ISO, "CCITT Recommendations X.400/ ISO IS 10021-1", Message Handling: System and Service Overview, CCITT/ISO, December 1988.
[CCITT/ISO88b] CCITT/ISO, "CCITT Recommendations X.420/ ISO IS 10021-7", Message Handling Systems: Interpersonal Messaging System, CCITT/ISO, December 1988.
[CCITT/ISO88c] CCITT/ISO, "CCITT Recommendations X.411/ ISO IS 10021-4", Message Handling Systems: Message Transfer System: Abstract Service Definition and Procedures, CCITT/ISO, December 1988.
[CCITT/ISO88d] CCITT/ISO, "Specification of Abstract Syntax Notation One (ASN.1)", CCITT Recommendation X.208 / ISO IS 8824, CCITT/ISO, December 1988.
[Crocker82a] Crocker, D., "Standard of the Format of ARPA Internet Text Messages", RFC 822, August 1982.
[Horton86a] Horton, M., "UUCP Mail Interchange Format Standard", RFC 976, February 1986.
[Kille84b] Kille, S., "Gatewaying between RFC 822 and JNT Mail", JNT Mailgroup Note 15, May 1984.
[Kille84a] Kille, S., Editor, "JNT Mail Protocol (revision 1.0)", Joint Network Team, Rutherford Appleton Laboratory, March 1984.
[Kille86a] Kille, S., "Mapping Between X.400 and RFC 822", UK Academic Community Report (MG.19) / RFC 987, June 1986.
[Kille87a] Kille, S., "Addendum to RFC 987", UK Academic Community Report (MG.23) / RFC 1026, August 1987.
[Kille89a] Kille, S., "A String Encoding of Presentation Address", UCL Research Note 89/14, March 1989.
[Kille89b] Kille, S., "Mapping Between Full RFC 822 and RFC 822 with Restricted Encoding", RFC 1137, December 1989.
[Larmouth83a] Larmouth, J., "JNT Name Registration Technical Guide", Salford University Computer Centre, April 1983.
[Mockapetris87a] Mockapetris, P., "Domain Names - Concepts and Facilities", RFC 1034, USC/Information Sciences Institute, November 1987.
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[Postel82a] Postel, J., "Simple Mail Transfer Protocol", RFC 821, USC/Information Sciences Institute, August 1982.
[Rose85a] Rose M., and E. Stefferud, "Proposed Standard for Message Encapsulation", RFC 934, January 1985.
[Systems85a] CEN/CENELEC/Information Technology/Working Group on Private Message Handling Systems, "FUNCTIONAL STANDARD A/3222", CEN/CLC/IT/WG/PMHS N 17, October 1985.
Security Considerations
Security issues are not discussed in this memo.
Author's Address
Steve Kille University College London Gower Street WC1E 6BT England