RFC 1148
Mapping between X.400(1988) / ISO 10021 and RFC 822
RFC 1148: Mapping between X.400(1988) / ISO 10021 and RFC 822 💌✨
okay bestie, this is RFC 1148, written by S. Kille at University College London, and it's dated March 1990 🎀. It updates RFC 822, RFC 987, RFC 1026, and RFC 1138. It doesn't obsolete RFC 987 or RFC 1026, since the text says its domain of application is different from theirs 🧚. Its whole job is making X.400(1988) / ISO 10021 mail and RFC 822 mail talk to each other 💖.
Status of This Memo 🌸
so this RFC suggests an email protocol mapping for the Internet community and the UK Academic Community, and it's literally asking people to discuss it and send ideas for making it better 🫶. it does NOT specify an Internet standard, ngl 💅. this edition includes material that got lost in editing 😭. distribution of this memo is unlimited 🦋.
This document describes a set of mappings that let systems running the CCITT X.400 (1988) Recommendations on Message Handling Systems / ISO IEC 10021 Message Oriented Text Interchange Systems (MOTIS) [CCITT/ISO88a] talk to systems using the RFC 822 mail protocol [Crocker82a] or protocols derived from RFC 822 🌈. the goal is to maximise the services offered across the boundary without 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, since its domain of application is different 💜.
Specification 🎀
this document specifies a mapping between two protocols 💅. this specification should be used when the mapping is performed on the Internet or in the UK Academic Community 🌈. this specification may be modified in the light of implementation experience, but no substantial changes are expected 🦋.
Table of Contents 📚
1. Overview ............................................... 2
1.1 X.400 ................................................. 2
1.2 RFC 822 ............................................... 3
1.3 The need for conversion ............................... 4
1.4 General approach ...................................... 4
1.5 Gatewaying Model ...................................... 5
1.6 RFC 987 ............................................... 7
1.7 Aspects not covered ................................... 8
1.8 Subsetting ............................................ 9
1.9 Document Structure .................................... 9
1.10 Acknowledgements ..................................... 10
2. Service Elements ....................................... 10
2.1 The Notion of Service Across a Gateway ................ 10
2.2 RFC 822 ............................................... 11
2.3 X.400 ................................................. 15
3. Basic Mappings ........................................ 24
3.1 Notation .............................................. 24
3.2 ASCII and IA5 ......................................... 25
3.3 Standard Types ........................................ 25
3.4 Encoding ASCII in Printable String .................... 28
4. Addressing ............................................. 29
4.1 A textual representation of MTS.ORAddress ............. 30
4.2 Basic Representation .................................. 30
4.3 EBNF.822-address <-> MTS.ORAddress .................... 34
4.4 Repeated Mappings ..................................... 43
4.5 Directory Names ....................................... 45
4.6 MTS Mappings .......................................... 45
4.7 IPMS Mappings ....... ................................. 48
5. Detailed Mappings ...................................... 52
5.1 RFC 822 -> X.400 ...................................... 52
5.2 Return of Contents .................................... 59
5.3 X.400 -> RFC 822 ...................................... 60
Appendix A Differences with RFC 987 ....................... 79
1. Introduction ........................................... 79
2. Service Elements ....................................... 80
3. Basic Mappings ......................................... 80
4. Addressing ............................................. 80
5. Detailed Mappings ...................................... 80
6. Appendices ............................................. 81
Appendix B Mappings specific to the JNT Mail .............. 81
1. Introduction ........................................... 81
2. Domain Ordering ........................................ 81
3. Acknowledge-To: ........................................ 81
4. Trace .................................................. 82
5. Timezone specification ................................. 82
6. Lack of 822-MTS originator specification ............... 82
Appendix C Mappings specific to UUCP Mail ................. 83
Appendix D Object Identifier Assignment ................... 83
Appendix E BNF Summary .................................... 84
Appendix F Format of address mapping tables ............... 91
References ................................................. 92Chapter 1: Overview 🌟
1.1. X.400 💼
this doc is about the CCITT 1988 X.400 Series Recommendations / ISO IEC 10021 Message Oriented Text Interchange Service (MOTIS) 💫. the ISO/CCITT standard gets called "X.400" in here, which is just a convenient shorthand 🫶. any reference to the 1984 CCITT Recommendations will be explicit, so no mix-ups 🙈. X.400 defines an Interpersonal Messaging System (IPMS) that uses a store and forward Message Transfer System 📬. this doc only cares about the IPMS, not the wider application of X.400 🎯. it's expected that X.400 will be implemented very widely 🔥.
1.2. RFC 822 📨
RFC 822 is the current specification of the messaging standard on the Internet 👑. it grew up alongside the network, going from the ARPANET (created by the Defense Advanced Research Projects Agency) all the way 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, and it's used with a bunch of different message transfer protocol environments 💅.
SMTP Networks 🦋
on the Internet and other TCP/IP networks, RFC 822 is used together 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, mostly 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 💀.
JNT Mail Networks 🇬🇧
a number of X.25 networks, particularly those associated with the UK Academic Community, use the JNT (Joint Network Team) Mail Protocol, also known as Greybook [Kille84a] ✉️. this is used with domains and name service specified by the JNT NRS (Name Registration Scheme) [Larmouth83a] 🎀.
the mappings specified here are appropriate for all of these networks 🫶✨.
1.3. The need for conversion 🔄
there's a huge community using RFC 822 based protocols for mail, and they'll want to talk to people using the IPMS provided by X.400 systems 🌈. this will also be needed when communities plan to move over to an X.400 IPMS, since conversion is needed for a smooth service transition 🦋. it's expected that there will be more than one gateway, and this specification will let them behave consistently 💅. the term gateway is used here for a component that performs the protocol mappings between RFC 822 and X.400 🧚. this is standard usage amongst mail implementors, but transport and network service implementors should note it carefully ⭐.
consistency between gateways is desirable, because it gives you:
- Consistent service to users. 💖
- The best service in cases where a message passes through multiple gateways. 🔥
1.4. General approach 🧠
there are a number of basic principles underlying the details of the specification 💫. these principles are goals, and they aren't achieved in every aspect of the specification 🙈.
- 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. 💅
- Subject to 1), functionality across a gateway should be as high as possible. 👑
- It is always a bad idea to lose information as a result of any transformation. Hence, it is a bad idea for a gateway to discard information in the objects it processes. This includes requested services which cannot be fully mapped. 😭
- 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. 🧚
- The specification should be reversible. That is, a double transformation should bring you back to where you started. 🦋
1.5. Gatewaying Model 🌉
1.5.1. X.400 ✨
Okay bestie, so X.400 defines the IPMS Abstract Service in X.420/ISO 10021-7, [CCITT/ISO88b], and it's made up of three basic services 💅
- Origination
- Reception
- Management
Management is a local interaction between the user and the IPMS, so it's not relevant to gatewaying 🙈 The first two services are all about operations that originate and receive these two objects:
- IPM (Interpersonal Message). This one has two components: a heading and a body. The body is a sequence of body parts, which can be basic components (like IA5 text, or G3 fax) or IP Messages. The heading is made of fields with end to end user information, like subject, primary recipients (To:), and importance. 📬
- IPN (Inter Personal Notification). This is a notification about receipt of a given IPM at the UA level. 🫶
The Origination service also lets you originate a probe, which is an object that tests whether a given IPM could be correctly received 🧚
The Reception service also lets you receive Delivery Reports (DR), which indicate delivery success or failure ✨
These IPMS Services use the Message Transfer (MT) Abstract Service [CCITT/ISO88c], and that one has three basic services of its own 🦋
- Submission (used by IPMS Origination)
- Delivery (used by IPMS Reception)
- Administration (used by IPMS Management)
Administration is a local issue, so it doesn't affect this standard. Submission and delivery mainly relate to the MTS Message (Envelope and Content), which carries an IPM or IPN (or other uninterpreted contents). The Envelope 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 defines the interaction between MTAs, along with the procedures for distributed operation. This service provides for transfer of MTS Messages, Probes, and Reports 👑
1.5.2. RFC 822
RFC 822 is based on the assumption that there is an underlying service, which we're calling the 822-MTS service 🎀 The 822-MTS service provides three basic functions:
- Identification of a list of recipients.
- Identification of an error return address.
- Transfer of an RFC 822 message.
It is possible to achieve 2) within the RFC 822 header. Some 822-MTS protocols, in particular SMTP, can provide additional functionality, but since these are neither mandatory in SMTP nor available in other 822-MTS protocols, they aren't 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 💖
1.5.3. The Gateway
Now that we've got this functional description of the two services, we can think about the functional nature of a gateway 🧠 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's necessary to consider that the IPM format definition, the IPMS Service Elements, the MTS Service Elements, and the 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 defined, so here they are 🌈 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:
- A Report (MTA, and MTS Services)
- An IPN (MTA, MTS, and IPMS Services)
- An IPM (MTA, MTS, and IPMS Services)
Probes (MTA Service) must be processed by the gateway, as discussed in Chapter 5. MTS Messages containing Content Types other than those defined by the IPMS are not mapped by the gateway, and should be rejected at the gateway 🚫
1.5.4. Repeated Mappings
The mappings specified here are designed to work where a message traverses multiple times between X.400 and RFC 822. This is often essential, particularly in the case of distribution lists 📨 However, in general this will lead to a level of service which is the lowest common denominator (approximately the services offered by RFC 822). In particular, there is no expectation of additional X.400 services being mapped, although this may be possible in some cases 🥲
1.6. RFC 987
Much of this work is based on the initial specification of RFC 987 and 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 so we can give good support to communities that will use full X.400 early on 🚀 This has 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's no advantage and some disadvantage in using the new mapping and then applying X.400 downgrading rules later on. 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 the one defined in RFC 987 ✨
Unnecessary change is usually a bad idea 🙅♀️ Changes on the RFC 822 side are avoided as far as possible, so RFC 822 users don't see arbitrary differences between systems conforming to this specification and those following RFC 987. Changes on the X.400 side are minimised, but they're more acceptable, due to the mapping onto a new set of services and protocols.
A summary of changes made is given in Appendix A 📝
1.7. Aspects not covered
There have been a number of cases where RFC 987 was used in a manner which was not intended 👀 This section makes 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. So it will be a poor choice for X.400 implementors to use RFC 987(88) as an interface, because there are too many aspects of X.400 that cannot be accessed through it. If a text interface is desired, a specification targeted at X.400, without RFC 822 restrictions, would be more appropriate 🎀
1.8. Subsetting
This proposal specifies a mapping which is appropriate for preserving services in existing RFC 822 communities. Implementations and specifications which subset this specification are strongly discouraged 🚫💅
1.9. Document Structure
This document has five chapters:
- Overview - this chapter.
- Service Elements - This describes the (end user) services mapped by a gateway.
- Basic mappings - This describes some basic notation used in Chapters 3-5, the mappings between character sets, and some fundamental protocol elements.
- Addressing - This considers the mapping between X.400 O/R names and RFC 822 addresses, which is a fundamental gateway component.
- Detailed Mappings - This describes the details of all other mappings.
There are also six appendices:
- A. Differences with RFC 987
- B. Mappings Specific to JNT Mail
- C. Mappings Specific to UUCP Mail
- D. Object Identifier Assignment
- E. BNF Summary
- F. Format of Address Tables
WARNING: THE REMAINDER OF THIS SPECIFICATION IS TECHNICALLY DETAILED. IT WILL NOT MAKE SENSE, EXCEPT IN THE CONTEXT OF RFC 822 AND X.400 (1988). DO NOT ATTEMPT TO READ THIS DOCUMENT UNLESS YOU ARE FAMILIAR WITH THESE SPECIFICATIONS. 🚨
1.10. Acknowledgements
This work was partly sponsored by the Joint Network Team. The workshop at UCL in June 1989 to work on this specification was also an IFIP WG 6.5 meeting 🌟
The work in this specification was substantially based on RFC 987, which had input from many people 🫶
Useful comments and suggestions were made by Pete Cowen (Nottingham Univ), Jim Craigie (JNT), Christian Huitema (Inria), Peter Lynch (Prime), Julian Onions (Nottingham Univ), Sandy Shaw (Edinburgh Univ), Einar Stefferud (NMA), and Peter Sylvester (GMD) 💜
Chapter 2 -- Service Elements ✨
This chapter considers the services offered across a gateway built according to this specification. It gives a view of the functionality provided by such a gateway for communication with users in the opposite domain. This chapter considers service mappings in the context of SINGLE transfers only, and not repeated mappings through multiple gateways 🦋
2.1. The Notion of Service Across a Gateway
RFC 822 and X.400 provide a number of services to the end user. This chapter describes the extent to which each service can be supported across an X.400 <-> RFC 822 gateway 💖 The cases considered are single transfers across such a gateway, although the problems of multiple crossings are noted where appropriate 🌸
2.1.1. Origination of Messages ✨
Okay bestie, so when a user originates a message there's a whole buffet of services on offer 🍓. Some imply actions, like actually delivering the thing to a recipient, and some are just slotting in known data, like filling out a subject field 💅. This bit covers, for each service, how well it survives the trip to a recipient reached through a gateway. There are three levels of support:
Supported: the matching protocol elements map well, so the service can be fully provided ✨Not Supported: the service can't be provided at all, because it's a complete mismatch 💀Partial Support: the service can be partly fulfilled 🌸
In the first two cases, the service just gets marked "Supported" or "Not Supported". Sometimes there's extra explanation if there are additional implications or the (non-)support isn't obvious 🙈. For partial support, the level gets summarised. When partial support is pretty good, it's described with a phrase like "Supported by use of.....". A super common case is when a service gets mapped onto a non-standard service on the other side of the gateway, which would have counted as support if it had been a standard one. In lots of cases that's basically equivalent to support 🫶. For partial support they also tell you the mechanism, so you can get a feel for how much support you're actually getting. And ngl, this section 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, that's considered supported, because 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 are described under X.400 💜.
2.1.2. Reception of Messages 📬
For reception, the list of service elements required to support this mapping is specified. This is really an indication of what a recipient might expect to see in a message that was remotely originated 👀.
2.2. RFC 822 🎀
RFC 822 doesn't explicitly define service elements as distinct from protocol elements. However, all of the RFC 822 header fields, with the exception of trace, can be regarded as corresponding to implicit RFC 822 service elements ✨.
2.2.1. Origination in RFC 822 🌸
A mapping mechanism 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, because it makes the information available to any X.400 implementations that are interested in these services. Communities that 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 listed below.
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 ofFrom:.Sender:Supported.Reply-To:Supported.To:Supported.Cc:Supported.Bcc:Supported.Message-Id:Supported.In-Reply-To:Supported, for a single reference. Where multiple references are given, partial support is given by mapping to "Cross Referencing Indication". This gives similar semantics.References:Supported.Keywords:Supported by use of a heading extension.Subject:Supported.Comments:Supported by use of 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, so they aren't accessible to the X.400 user as addresses. In principle, fuller support would be possible by mapping onto a forwarded IP Message, but this is not suggested 🙃.- Other Fields: in particular
X-*fields, and "illegal" fields in common usage (e.g., "Fruit-of-the-day:") are supported by use of heading extensions 🍓.
2.2.2. Reception by RFC 822 📥
This considers reception by an RFC 822 User Agent of a message originated in an X.400 system and transferred across a gateway. The following standard services (headers) may be present in such a message:
Date:From:Sender:Reply-To:To:Cc:Bcc:Message-Id:In-Reply-To:References:Subject:
The following non-standard services (headers) may be present. These are defined in more detail in Chapter 5 (5.3.4, 5.3.6, 5.3.7) 🧚:
Autoforwarded:Content-Identifier:Conversion:Conversion-With-Loss:Delivery-Date:Discarded-X400-IPMS-Extensions:Discarded-X400-MTS-Extensions:DL-Expansion-History:Deferred-Delivery:Expiry-Date:Importance:Incomplete-Copy:Language:Latest-Delivery-Time:Message-Type:Obsoletes:Original-Encoded-Information-Types:Originator-Return-Address:Priority:Redirection-History:Reply-By:Requested-Delivery-Method:Sensitivity:X400-Content-Type:X400-MTS-Identifier:X400-Originator:X400-Received:X400-Recipients:
2.3. X.400 💜
2.3.1. Origination in X.400 🦋
When mapping services from X.400 to RFC 822 that aren't 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 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, each marked with a different comment:
N/A (local): these elements are only applicable to User Agent / Message Transfer Agent interaction, 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), so they 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.N/A (MS): these services are only applicable to Message Store (i.e., a local service).
Finally, some service elements are not supported. In particular, the new security services are not mapped onto RFC 822. Unless otherwise indicated, the behaviour of service elements marked as not supported will depend on the criticality marking supplied by the user. If the element is marked as critical for transfer or delivery, a non-delivery notification will be generated. Otherwise, the service request will be ignored 🚫.
2.3.1.1. Basic Interpersonal Messaging Service 💌
These are the mandatory IPM services as listed in Section 19.8 of X.400 / ISO/IEC 10021-1, listed here in the order given. Section 19.8 has cross references to short definitions of each service 📚.
- Access management: N/A (local).
- Content Type Indication: Supported by a new RFC 822 header (
Content-Type:). - Converted Indication: Supported by a new RFC 822 header (
X400-Received:). - Delivery Time Stamp Indication: N/A (reception).
- IP Message Identification: Supported.
- Message Identification: Supported, by use of a new RFC 822 header (
X400-MTS-Identifier). This new header is required, as X.400 has two message-ids whereas RFC 822 has only one (see previous service). - Non-delivery Notification: Not supported, although in general an RFC 822 system will return error reports by use of IP messages. In other service elements, this pragmatic result can be treated as effective support of this service element 🤷♀️.
- Original Encoded Information Types Indication: Supported as a new RFC 822 header (
Original-Encoded-Information-Types:). - Submission Time Stamp Indication: Supported.
- Typed Body: Some types supported. IA5 is fully supported.
ForwardedIPMessageis supported, with some loss of information. Other types get some measure of support, dependent on X.400 facilities for conversion to IA5. This will only be done where content conversion is not prohibited 🍰. - User Capabilities Registration: N/A (local).
2.3.1.2. IPM Service Optional User Facilities
Okay bestie, this is the big checklist of X.400's optional, user-selectable IPM services 📋✨. It's the list from Section 19.9 of X.400 / ISO/IEC 10021- 1, in the order given there, and Section 19.9 has cross references to short definitions of each one 🦋. Here's how each one shakes out for the gateway 💅
- Additional Physical Rendition: N/A (PDAU).
- Alternate Recipient Allowed: Not supported 🙅♀️. RFC 822 has nothing equivalent to banning alternate recipient assignment. An RFC 822 system can happily send an undeliverable message to a local postmaster, so the gateway can't stop alternative recipients on the RFC 822 side. This service is really about giving the user control over whether an alternate recipient is allowed. This specification requires messages to be transferred to RFC 822 no matter what was requested, so this one is a no-go 😭
- Authorising User's Indication: Supported ✅.
- Auto-forwarded Indication: Supported as a new RFC 822 header (
Auto-Forwarded:) 💌. - Basic Physical Rendition: N/A (PDAU).
- Blind Copy Recipient Indication: Supported ✅.
- Body Part Encryption Indication: Supported through a new RFC 822 header (
Original-Encoded-Information-Types:). Real talk though, in most cases the body part in question won't be mappable 🙈. - Content Confidentiality: Not supported 💀.
- Content Integrity: Not supported 💀.
- Conversion Prohibition: Supported 🔥. But only messages with IA5 body parts get mapped, along with body parts that contain only IA5, and Forwarded IP Messages (which follow the same restrictions, recursively) 🧚.
- 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 before the gateway. A new RFC 822 header (
Deferred-Delivery:) carries the info about this service over to the recipient 🎀. - Deferred Delivery Cancellation: N/A (local).
- Delivery Notification: Supported 🔔. This happens at the gateway, so the gateway sends the notification to the originator. If the 822-MTS protocol is JNT Mail, the recipient UA may also send one.
- Delivery via Bureaufax Service: N/A (PDAU).
- Designation of Recipient by Directory Name: N/A (local).
- Disclosure of Other Recipients: Supported through a new RFC 822 header (
X400-Recipients:). It's descriptive info for the RFC 822 recipient, and it can't be reverse mapped 🔄. - DL Expansion History Indication: Supported through a new RFC 822 header (
DL-Expansion-History:) 📜. - DL Expansion Prohibited: Okay, so "Distribution List" here means an MTS-supported list, the X.400 way. RFC 822 has no such thing. RFC 822 distribution lists are an informal redistribution mechanism and sit outside this control. Messages go to RFC 822 whether or not this is requested. So in theory it's supported, even though it may look like it isn't in practice 🫠.
- Express Mail Service: N/A (PDAU).
- Expiry Date Indication: Supported as a new RFC 822 header (
Expiry-Date:). Generally, don't expect any automatic action from it ⏳. - Explicit Conversion: N/A (prior).
- Forwarded IP Message Indication: Supported, with some loss of information 📨. The message gets forwarded in an RFC 822 body, so it can only be read visually 👀.
- Grade of Delivery Selection: N/A (PDAU)
- Importance Indication: Supported as a new RFC 822 header (
Importance:) ‼️. - Incomplete Copy Indication: Supported as a new RFC 822 header (
Incomplete-Copy:) 📄. - Language Indication: Supported as a new RFC 822 header (
Language:) 🌍. - Latest Delivery Designation: Not supported. But a new RFC 822 header (
Latest-Delivery-Time:) exists, which the recipient may use 🕰️. - 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, because RFC 822 can't formalise the structuring 🧩.
- 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 a new RFC 822 header (
Obsoletes:) ♻️. - Ordinary Mail: N/A (PDAU).
- Originator Indication: Supported ✅.
- Originator Requested Alternate Recipient: Not supported, but it gets placed as a comment next to the address (
X400-Recipients:) 💬. - Physical Delivery Notification by MHS: N/A (PDAU).
- Physical Delivery Notification by PDS: N/A (PDAU).
- Physical Forwarding Allowed: Supported through a comment in a new RFC 822 header (
X400-Recipients:), tied to the recipient in question 📬. - Physical Forwarding Prohibited: Supported through a comment in a new RFC 822 header (
X400-Recipients:), tied to the recipient in question 📭. - Prevention of Non-delivery notification: Supported, since RFC 822 can't generate delivery notifications. In practice, errors come back as IP Messages, so this one may look unsupported (see Non-delivery Notification) 🙃.
- Primary and Copy Recipients Indication: Supported ✅.
- Probe: Supported at the gateway, meaning 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 here means MTS-supported redirection, the X.400 way. RFC 822 doesn't have that. RFC 822 redirection (like aliasing) is an informal mechanism and sits outside this control. Messages go to RFC 822 whether or not it's requested. So in theory it's supported, though it may look like it isn't in practice 🌀.
- Registered Mail: N/A (PDAU).
- Registered Mail to Addressee in Person: N/A (PDAU).
- Reply Request Indication: Supported as a comment next to the 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 required services have to be handled at submission time. Any such request gets passed through the gateway as a comment attached to the recipient in question 🗒️.
- Return of Content: In principle this is N/A, since non-delivery notifications aren't supported. In practice, most RFC 822 systems send back some or all of the content along with the IP Message that signals an error (see Non-delivery Notification) 📦.
- Sensitivity Indication: Supported as a new RFC 822 header (
Sensitivity:) 🫣. - Special Delivery: N/A (PDAU).
- Stored Message Deletion: N/A (MS).
- Stored Message Fetching: N/A (MS).
- Stored Message Listing: N/A (MS).
- Stored Message Summary: N/A (MS).
- Subject Indication: Supported ✅.
- Undeliverable Mail with Return of Physical Message: N/A (PDAU).
- Use of Distribution List: In principle this only applies to X.400 supported distribution lists (see DL Expansion Prohibited). In theory this one is N/A (prior). In practice, since RFC 822 lists are informal, it can be regarded as supported 🎉.
2.3.2. Reception by X.400
2.3.2.1. Standard Mandatory Services
Okay so this is the list of standard IPM mandatory user facilities that may be required for an X.400 UA to receive RFC 822 originated mail 📥🌸.
- Content Type Indication
- Delivery Time Stamp Indication
- IP Message Identification
- Message Identification
- Non-delivery Notification
- Original Encoded Information Types Indication
- Submission Time Stamp Indication
- Typed Body
2.3.2.2. Standard Optional Services
Next up are the standard IPM optional user facilities that may be required for an X.400 UA to receive RFC 822 originated mail 🦋.
- Authorising User's Indication
- Blind Copy Recipient Indication
- Cross Referencing Indication
- Originator Indication
- Primary and Copy Recipients Indication
- Replying IP Message Indication
- Subject Indication
2.3.2.3. New Services
This one's a glow-up 🌈. A new service called "RFC 822 Header Field" gets defined using the extension facilities. It lets any RFC 822 header field be represented, and it may show up in RFC 822 originated messages that an X.400 UA receives 💖.
Chapter 3 -- Basic Mappings ✨
3.1. Notation
Okay, so here's the deal 🧠. X.400 protocols are encoded in a structured way according to ASN.1, whereas RFC 822 is text encoded. To define a detailed mapping, you have to refer to detailed protocol elements in each format, so this section describes a notation that does exactly that 💅.
3.1.1. RFC 822 🎀
okay bestie, so structured text is defined using the Extended Backus Naur Form (EBNF) from Section 2 of RFC 822 [Crocker82a] 💅 In the EBNF definitions in this spec, the syntax rules in Appendix D of RFC 822 are assumed ✨ When these EBNF tokens show up outside an EBNF definition, they get the string "822." stuck on the front, like 822.addr-spec 🦋 Any extra syntax rules we need across the whole spec are defined in this chapter 🌸
The EBNF gets used in two ways, and it's giving a lot of clarity 👑
- 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) 💖 - To describe the structure of IA5 or ASCII information that is not in an RFC 822 message. In these cases, tokens will either be self delimiting, or be delimited by self delimiting tokens. Comments and LWSP are not used as delimiters 🧚
3.1.2. ASN.1 🌈
an element gets referred to with this syntax, defined in EBNF, and it's so neat 🦋
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 these service specs, no cap 💅
IPMSIPMSInformationObjects defined in Annex E of X.420 / ISO 10021-7.MTSMTSAbstractService defined in Section 9 of X.411 / ISO 10021-4.MTAMTAAbstractService defined in Section 13 of X.411 / ISO 10021-4.
the first EBNF.identifier names a type or value key in the context of the defined service specification 🔥 subsequent EBNF.identifiers name a value label or type in the context of the first identifier (SET or SEQUENCE) 🫶 EBNF.context marks a context tag, and it's used where there's 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 also refers to element values. So MTS.EncodedInformationTypes.[0].g3Fax refers to a value of MTS.EncodedInformationTypes.[0] 💅
3.2. ASCII and IA5 🍓
a gateway will interpret all IA5 as ASCII, so mapping between these forms is only conceptual 🌸
3.3. Standard Types 👑
there's a need to convert between ASCII text and some of the types defined in ASN.1 [CCITT/ISO88d] 💖 for each case, there's an EBNF syntax definition for use across this whole spec, which leads to a mapping between ASN.1 and an EBNF construct 🦋
all EBNF syntax definitions of ASN.1 types are in lower case, whereas ASN.1 types are referred to with the first letter in upper case 🌈 except as noted, all mappings are symmetrical 🫶
3.3.1. Boolean ✨
Boolean is encoded as:
boolean = "TRUE" / "FALSE"3.3.2. NumericString 🧚
NumericString is encoded as:
numericstring = *DIGIT3.3.3. PrintableString 🌸
PrintableString is a restricted IA5String, defined as:
printablestring = *( ps-char )
ps-restricted-char = 1DIGIT / 1ALPHA / " " / "'" / "+"
/ "," / "-" / "." / "/" / ":" / "=" / "?"
ps-delim = "(" / ")"
ps-char = ps-delim / ps-restricted-charthis can be used to represent real printable strings in EBNF 💅
3.3.4. T.61String 💜
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's also a need to represent Teletex Strings in ASCII, for some aspects of O/R Address 😭 for these, this encoding is used:
teletex-string = *( ps-char / t61-encoded )
t61-encoded = "{" 1* t61-encoded-char "}"
t61-encoded-char = 3DIGITcommon characters are mapped simply 💖 other octets are mapped using a quoting mechanism similar to the printable string mechanism. Each octet is represented as 3 decimal digits 🌈
there are a number of places where a string may have a Teletex and/or Printable String representation, and this BNF is used to represent that 🧚
teletex-and-or-ps = [ printablestring ] [ "*" teletex-string ]the natural mapping is restricted to EBNF.ps-char, in order to make the full BNF easier to parse ✨
3.3.5. UTCTime 🌸
both UTCTime and the RFC 822 822.date-time syntax contain: Year (lowest two digits), Month, Day of Month, hour, minute, second (optional), and Timezone. 822.date-time also has an optional day of the week, but that's redundant 🙈 so a symmetrical mapping can be made between these constructs 🫶
Note: In practice, a gateway will need to parse various illegal variants on 822.date-time. In cases where 822.date-time cannot be parsed, it is recommended that the derived UTCTime is set to the value at the time of translation.
the UTCTime format which specifies the timezone offset should be used 🦋
3.3.6. Integer 💅
a basic ASN.1 Integer will be mapped onto EBNF.numericstring 🔥 in many cases ASN.1 will enumerate Integer values or use ENUMERATED. An EBNF encoding called 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, adding an appropriate text label is strongly encouraged 💖
labelled-integer ::= [ key-string ] "(" numericstring ")"
key-string = *key-char
key-char = <a-z, A-Z, 1-9, and "-">3.3.7. Object Identifier 🎀
object identifiers are represented in a form similar to the one given in ASN.1 🌈 the numbers are mandatory, to ease encoding 🧚 it is recommended that as many strings as possible are used, to facilitate user recognition 🫶
object-identifier ::= [ defined-value ] oid-comp-list
oid-comp-list ::= oid-comp oid-comp-list
| oid-comp
defined-value ::= key-string
oid-comp ::= [ key-string ] "(" numericstring ")"3.4. Encoding ASCII in Printable String 💜
some information in RFC 822 is represented in ASCII, and it needs to be mapped into X.400 elements encoded as printable string 🦋 that's why we need a mechanism to represent ASCII encoded as PrintableString ✨
here's a structured subset of EBNF.printablestring that can be used to encode ASCII in the PrintableString character set 💅
ps-encoded = *( ps-restricted-char / ps-encoded-char )
ps-encoded-char = "(a)" ; (@)
/ "(p)" ; (%)
/ "(b)" ; (!)
/ "(q)" ; (")
/ "(u)" ; (_)
/ "(l)" ; "("
/ "(r)" ; ")"
/ "(" 3DIGIT ")"the 822.3DIGIT in EBNF.ps-encoded-char must have range 0-127, and it's interpreted in decimal as the matching 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, aren't included in PrintableString, but they're super 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's only applied to a Domain defined attribute, which will have been generated by use of this specification, so a value such as "(" would not be possible 🦋
to encode ASCII as PrintableString, the EBNF.ps-encoded syntax is used, with all EBNF.ps-restricted-char mapped directly 💅 all other 822.CHAR are encoded as EBNF.ps-encoded-char 🧚
to encode PrintableString as ASCII, parse PrintableString as EBNF.ps-encoded, and then reverse the previous mapping 🫶 if the PrintableString cannot be parsed, then the mapping is being applied in to an inappropriate value, and an error should be given to the procedure doing the mapping 😭 in some cases, it may be preferable to pass the printable string through unaltered 🌸
some examples are now given! Note the arrows which indicate asymmetrical mappings 🦋
PrintableString ASCII
'a demo.' <-> 'a demo.'
foo(a)bar <-> foo@bar
(q)(u)(p)(q) <-> "_%"
(a) <-> @
(A) <-> @
(l)a(r) <-> (a)
(126) <-> ~
( -> (
(l) <-> (Chapter 4 -- Addressing ✨
addressing is probably the trickiest problem of an X.400 <-> RFC 822 gateway 😭 that's why it gets its own chapter 💅 this chapter also, as a side effect, 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-specin 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 🫶
the basic X.400 O/R Address, which the MTS uses for routing, is defined by MTS.ORAddress 💖 in IPMS, the MTS.ORAddress is encapsulated within IPMS.ORDescriptor 🌸
it can be seen that RFC 822 822.address must be mapped with IPMS.ORDescriptor, and that RFC 822 EBNF.822-address must be mapped with MTS.ORAddress 👑
4.1. A textual representation of MTS.ORAddress 💜
MTS.ORAddress is structured as a set of attribute value pairs 🎀 it's clearly necessary to be able to encode this in ASCII for gatewaying purposes 🔥 all aspects should be encoded, in order to guarantee return of error messages, and to optimise third party replies 🦋
4.2. Basic Representation ✨
okay so an O/R Address has a bunch of structured and unstructured attributes 🎀. For each unstructured one, we specify a key and an encoding. For structured ones, the X.400 attribute gets mapped onto one or more attribute value pairs 💅. For domain defined attributes, each element of the sequence maps onto a triple (a key and two values), and both values have the same encoding. The attributes are listed below, with the 1984 ones in the first part of the table. Each attribute comes with a reference to the relevant sections in X.402 / ISO 10021-2, plus the extension identifier for the 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
88 Attributes
MTS.CommonName CN P/T 18.3.2 1
MTS.TeletexCommonName CN P/T 18.3.2 2
MTS.TeletexOrganizationName O P/T 18.3.9 3
MTS.TeletexPersonalName PN P/T 18.3.12 4
MTS.TeletexPersonalName.surname S P/T 18.3.12 4
MTS.TeletexPersonalName.given-name G P/T 18.3.12 4
MTS.TeletexPersonalName.initials I P/T 18.3.12 4
MTS.TeletexPersonalName
.generation-qualifier GQ P/T 18.3.12 4
MTS.TeletexOrganizationalUnitNames
.value OU P/T 18.3.10 5
MTS.TeletexDomainDefinedAttribute
.value DD P/T 18.1 6
MTS.PDSName PD-SYSTEM P 18.3.11 7
MTS.PhysicalDeliveryCountryName PD-C P 18.3.13 8
MTS.PostalCode POSTCODE P 18.3.19 9
MTS.PhysicalDeliveryOfficeName PD-OFFICE P/T 18.3.14 10
MTS.PhysicalDeliveryOfficeNumber PD-OFFICE-NUM P/T 18.3.15 11
MTS.ExtensionORAddressComponents PD-EXT-D P/T 18.3.4 12
MTS.PhysicalDeliveryPersonName PD-PN P/T 18.3.17 13
MTS.PhysicalDelivery PD-O P/T 18.3.16 14
OrganizationName
MTS.ExtensionPhysicalDelivery
AddressComponents PD-EXT-LOC P/T 18.3.5 15
MTS.UnformattedPostalAddress PD-ADDRESS P/T 18.3.25 16
MTS.StreetAddress STREET P/T 18.3.22 17
MTS.PostOfficeBoxAddress PO-BOX P/T 18.3.18 18
MTS.PosteRestanteAddress POSTE-RESTANTE P/T 18.3.20 19
MTS.UniquePostalName PD-UNIQUE P/T 18.3.26 20
MTS.LocalPostalAttributes PD-LOCAL P/T 18.3.6 21
MTS.ExtendedNetworkAddress
.e163-4-address.number NET-NUM N 18.3.7 22
MTS.ExtendedNetworkAddress
.e163-4-address.sub-address NET-SUB N 18.3.7 22
MTS.ExtendedNetworkAddress
.psap-address NET-PSAP X 18.3.7 22
MTS.TerminalType NET-TTYPE I 18.3.24 23Next up, the keys that tell you which EBNF encodings go with the ASCII representation of MTS.ORAddress 🌸
Key Encoding
P printablestring
N numericstring
T teletex-string
P/T teletex-and-or-ps
I labelled-integer
X presentation-addressThe BNF for presentation-address is taken from the specification "A String Encoding of Presentation Address" [Kille89a] 📚
In most cases the EBNF encoding maps straight onto the ASN.1 encoding of the attribute, easy peasy 🙌 There are a few exceptions though. When an attribute can be encoded as either a PrintableString or a 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 🔢
The P/T (teletex-and-or-ps) representation shows up a lot too. When the key maps to a single attribute, that choice gets reflected in the encoding of the attribute (attributes 10-21). For most of the 1984 attributes and common name, there's a printablestring version and a teletex version. That pair gets mapped onto the single component here, which gives a clean mapping for the common cases where only one form of the name is used 🫶
4.2.1. Encoding of Personal Name
ngl, handling Personal Name and Teletex Personal Name based purely on the EBNF.standard-type syntax from above would be kinda clumsy 😭 So it makes sense to use the "human" conventions for encoding these parts. The syntax below gives a clean encoding for the common O/R address cases where:
- There is no generational qualifier
- Initials contain only letters
- Given Name does not contain full stop ("."), and is at least two characters long.
- If Surname contains full stop, then it may not be in the first two characters, and either initials or given name is present.
Here's the EBNF:
encoded-pn = [ given "." ] *( initial "." ) surname
given = 2*<ps-char not including ".">
initial = ALPHA
surname = printablestringThis can be used to map 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 get assigned directly, and all EBNF.initial tokens get concatenated without any full stops in between to generate the initials 💖
For an O/R address that follows the restrictions above, you can derive a string in the natural way, and in that case the mapping is reversible ✨ For example:
GivenName = "Marshall"
Surname = "Rose"
Maps with "Marshall.Rose"
Initials = "MT"
Surname = "Rose"
Maps with "M.T.Rose"
GivenName = "Marshall"
Initials = "MT"
Surname = "Rose"
Maps with "Marshall.M.T.Rose"Note that X.400 suggests Initials is used to encode ALL initials 👀 So the proposed encoding is "natural" when either GivenName or Initials is present, but not both. The case where both are present can still be encoded, but it appears to be contrived 🙈
4.2.2. Standard Encoding of MTS.ORAddress
Given this structure, we can write a BNF representation of an O/R Address 🧚
std-or-address = 1*( "/" attribute "=" value ) "/"
attribute = standard-type
/ "RFC-822"
/ registered-dd-type
/ dd-key "." std-printablestring
standard-type = key-string
registered-dd-type
= key-string
dd-key = key-string
value = std-printablestring
std-printablestring
= *( std-char / std-pair )
std-char = <"{", "}", "*", and any ps-char
except "/" and "=">
std-pair = "$" ps-charThe standard-type can be any key from the table in Section 4.2, except PN and DD. After quote removal, the value 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 get 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 by the encoding, and aligned to either the teletex or printable string form. Key and value should have the same encoding 🌈
If the 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 a registered-dd-type, which means it's 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 that can be done at a gateway 🔥
4.3. EBNF.822-address <-> MTS.ORAddress
Ideally the mapping would be totally symmetrical and global, so addresses could be referred to transparently in the remote system, with the choice of gateway left to the Message Transfer Service 🌍 But there are two fundamental reasons why that isn't possible:
- The syntaxes are different enough to make this awkward.
- In the general case, there wouldn't be the administrative co-operation between the X.400 and RFC 822 worlds that this would need 😩
So an asymmetrical mapping is defined instead, which can become symmetrical wherever there is appropriate administrative control 💜
4.3.1. X.400 encoded in RFC 822 🌸
okay so this is where it gets spicy bestie 🫶. The std-or-address syntax is used to encode O/R Address info in the 822.local-part of EBNF.822-address. Extra O/R Address info can be hung off the 822.domain component too 💅. This can't be used in the general case, basically because of character set drama and the fact that X.400 O/R Addresses have no fixed order 🙈. The only way to fit the full PrintableString character set into a domain is the 822.domain-ref syntax (aka 822.atom), and that's likely to cause problems on loads of systems 💀. In practice, the domain character set is smaller than RFC 822's anyway, because domain conventions and policy restrict it even more.
A generic 822.address is a 822.local-part plus a sequence of 822.domains, for example <@domain1,@domain2:user@domain3>. Everything except the 822.domain tied to the 822.local-part (domain3 in this case) should be considered to specify routing inside the RFC 822 world, and the gateway won't interpret it 🦋. Those routing domains may still have identified the gateway from within the RFC 822 world, though.
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 can also identify the gateway from within the RFC 822 world ✨. This final 822.domain can be used to work out some O/R Address attributes. These attributes form a hierarchy, and the domain can specify them. In order of hierarchy, they are:
- Country
- ADMD
- PRMD
- Organisation
- Organisational Unit
There may be multiple Organisational Units 🧚.
Domain specifications can be associated with some set of attributes, and that association works hierarchically. For example, if a domain implies ADMD, it also implies country. Subdomains under it are associated according to the O/R Address hierarchy. Like this:
=> "AC.UK" might be associated with
C="GB", ADMD="GOLD 400", PRMD="UK.AC"
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 kept, instead of just using plain subdomains 👑:
- As a shorthand to avoid redundant X.400 information. For instance, there will often be only one ADMD per country, so it doesn't need to be given explicitly.
- To deal with cases where attribute values don't 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 was chosen because it's the one the various domain service administrations picked 💖.
- To deal with missing elements in the hierarchy. A domain may be associated with an omitted attribute alongside several present ones. When doing 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 an 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 only needs to be known by the gateways relaying between the RFC 822 world and the O/R Address space associated with the mapping in question 🌈. It is desirable, though, for all gateways to know these mappings, so third party addresses map optimally. A format for exchanging this information is defined in Appendix F.
The remaining attributes are encoded on the LHS, using the EBNF.std-or-address syntax. For example:
/I=J/S=Linnimouth/GQ=5/@Marketing.Widget.COMencodes the MTS.ORAddress consisting of:
MTS.CountryName = "TC"
MTS.AdministrationDomainName = "BTT"
MTS.OrganizationName = "Widget"
MTS.OrganizationalUnitNames.value = "Marketing"
MTS.PersonalName.surname = "Linnimouth"
MTS.PersonalName.initials = "J"
MTS.PersonalName.generation-qualifier = "5"The first three attributes are determined by the domain Widget.COM. Then the first element of OrganizationalUnitNames is determined systematically, and the remaining attributes are encoded on the LHS. In an extreme case, all of the attributes will be on the LHS. Since the domain can't be null, the RHS will simply be a domain indicating the gateway 🍓.
The RHS (domain) encoding is designed to handle common addresses cleanly, 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. Other forms of O/R Address, and teletex encoded attributes, will require an LHS encoding 💜.
There's also a further mechanism to simplify encoding of common cases. It applies where the only attributes to be encoded on the LHS are (non-Teletex) Personal Name attributes that 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 wasn't 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 used to select appropriate gateways for the corresponding O/R Address space. In most cases, this is done by registering the higher levels and assuming the gateway can handle the lower levels ⭐.
4.3.2. RFC 822 encoded in X.400 🦋
In some cases, the encoding defined above may be reversed, to give a "natural" encoding of genuine RFC 822 addresses. This depends largely on the allocation of appropriate management domains 🌸.
The general case is mapped using 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. How the ASCII string gets interpreted depends on the context of the gateway 🔥.
- In the context of RFC 822, and RFC 1034 [Crocker82a, Mockapetris87a], the string can be used directly.
- In the context of the JNT Mail protocol, and the NRS [Kille84a, Larmouth83a], the string should be interpreted according to Mailgroup Note 15 [Kille84b].
- 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 is interpreted. This might be a Management Domain, or some part of a Management Domain that identifies a gateway MTA. For example:
C = "GB"
ADMD = "GOLD 400"
PRMD = "UK.AC"
O = "UCL"
OU = "CS"
"RFC-822" = "Jimmy(a)WIDGET-LABS.CO.UK"OR
C = "TC"
ADMD = "Wizz.mail"
PRMD = "42"
"rfc-822" = "Postel(a)venera.isi.edu"Note that in each case the PrintableString encoding of "@" is "(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. So this scheme can be used with varying levels of Management Domain co-operation 🧚.
4.3.3. Component Ordering 👑
In most cases, ordering of O/R Address components isn't significant for the mappings specified. However, Organisational Units (printable string and teletex forms) and Domain Defined Attributes are specified as SEQUENCE in MTS.ORAddress, so their order may be significant. This specification needs to take account of that:
- To allow consistent mapping into the domain hierarchy.
- To ensure preservation of order over multiple mappings.
There are three places where an order must be specified 💖:
- 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 there for the following reasons:
- Alignment to the hierarchy of other components in RFC 822 addresses (thus, Organisational Units will appear in the same order, whether encoded on the RHS or LHS). Note the differences of JNT Mail as described in Appendix B.
- Backwards compatibility with RFC 987/1026.
- To ensure that gateways generate consistent addresses. This is both to help end users, and to generate identical message ids.
Further, it is recommended that all other attributes are generated according to this ordering, so that all attributes so encoded follow a consistent hierarchy.
There will be some cases where an X.400 O/R address of this encoding is 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.
- For the Organisational Units (OU) in MTS.ORAddress, the first OU in the SEQUENCE is the most significant, as specified in X.400.
- For the Domain Defined Attributes in MTS.ORAddress, the first Domain Defined Attribute in the SEQUENCE is the most significant.
Note that although this ordering is mandatory for this mapping, there are NO implications on ordering significance within X.400, where this is a Management Domain issue 🌈.
4.3.4. RFC 822 -> X.400 💌
Okay bestie, so there are two basic cases here 💅:
- X.400 addresses encoded in RFC 822. This also includes RFC 822 addresses that have reversible encodings.
- "Genuine" RFC 822 addresses.
The mapping SHOULD proceed as follows, by first assuming case 1) ✨.
STAGE I.
- If the 822-address is not of the form:
local-part "@" domainGo to stage II.
NOTE: It MAY be appropriate to reduce a source route address to this form by removing all but 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. 🙈
- Attempt to parse EBNF.domain as:
*( domain-syntax "." ) known-domainWhere 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 EBNF.domain-syntax component. If the domain explicitly identifies the gateway, allocate no attributes. 🧚
- If the local-part contains any characters not in PrintableString, go to stage II.
- 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. 🌸
- 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.
- 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.
- Build the O/R Address from this information. 🎀
STAGE II.
This will only be reached if the RFC 822 EBNF.822-address is not a valid X.400 encoding. If the address is an 822-MTS recipient address, it MUST be rejected, as there is a need to interpret such an address in X.400. For the 822-MTS return address, and any addresses in the RFC 822 header, they SHOULD now be encoded as RFC 822 addresses in an X.400 O/R Name 🦋:
- Convert the EBNF.822-address to PrintableString, as specified in Chapter 3.
- The "RFC-822" domain defined attribute SHOULD be generated from this string.
- 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 of MTS.ub-domain-defined-attribute-value-length (128). If this is exceeded by a mapping at the MTS level, then the gateway SHOULD reject the message in question. If this occurs at the IPMS level, then the action SHOULD depend on the policy being taken, which is discussed in Section 5.1.3. 🚨
4.3.5. X.400 -> RFC 822 🌈
There are two basic cases:
- RFC 822 addresses encoded in X.400.
- "Genuine" X.400 addresses. This MAY include symmetrically encoded RFC 822 addresses.
When an MTS Recipient O/R Address is interpreted, gatewaying will be selected if there is a single "RFC-822" domain defined attribute present. In this case, use mapping A. For other O/R Addresses which:
- Contain the special attribute.
AND
- Identify 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
- 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.
- For all string encoded attributes, remove any leading or trailing spaces, and replace adjacent spaces with a single space.
- 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.
- 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 a subdomain, as 822.local-part cannot be null. 🌷
- 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 an 822.local-part using the EBNF.std-or-address syntax. If necessary, the 822.quoted-string encoding SHOULD be used.
If the derived 822.local-part can only be encoded by use of 822.quoted-string, then use of the mapping defined in [Kille89b] MAY be appropriate. Use of this mapping is discouraged. 🫶
4.4. Repeated Mappings 🔁
The mappings defined are symmetrical and reversible across a single gateway. The symmetry is particularly useful in cases of (mail exploder type) distribution list expansion. For example, an X.400 user sends to a list on an RFC 822 system which they belong 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, 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.XYThis 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.XYHere, use of the gateway is transparent. ✨
Mappings will only be symmetrical where mapping tables are defined. In other cases, the reversibility is more important, due to the (far too frequent) cases where RFC 822 and X.400 services are partitioned. 🥲
The syntax MAY be used to source route. THIS IS STRONGLY DISCOURAGED. For example:
X.400 -> RFC 822 -> X.400
C = "UK"
ADMD = "Gold 400"
PRMD = "UK.AC"
"RFC-822" = "/PN=Duval/DD.Title=Manager/(a)Inria.ATLAS.FR"This will be sent to an arbitrary UK Academic Community gateway by X.400. Then it will be sent by JNT Mail to another gateway determined by the domain Inria.ATLAS.FR (FR.ATLAS.Inria). This will then derive the X.400 O/R Address:
C = "FR"
ADMD = "ATLAS"
PRMD = "Inria"
PN.S = "Duval"
"Title" = "Manager"Similarly:
RFC 822 -> X.400 -> RFC 822
"/C=UK/ADMD=BT/PRMD=AC/RFC-822=jj(a)seismo.css.gov/"
@monet.berkeley.eduThis will be sent to monet.berkeley.edu by RFC 822, then to the AC PRMD by X.400, and then to jj@seismo.css.gov by RFC 822. 🦋
4.5. Directory Names 📇
Directory Names are an optional part of O/R Name, along with O/R Address. The RFC 822 addresses are mapped onto the O/R Address component. As there is no functional mapping for the Directory Name on the RFC 822 side, a textual mapping should be used. There is no requirement for reversibility in terms of the goals of this specification. There may be some loss of functionality in terms of third party recipients where only a directory name is given, but this seems preferable to the significant extra complexity of adding a full mapping for Directory Names. 🌟
4.6. MTS Mappings 📬
The basic mappings at the MTS level are:
1) 822-MTS originator ->
MTS.PerMessageSubmissionFields.originator-name
MTS.OtherMessageDeliveryFields.originator-name ->
822-MTS originator
2) 822-MTS recipient ->
MTS.PerRecipientMessageSubmissionFields
MTS.OtherMessageDeliveryFields.this-recipient-name ->
822-MTS recipient822-MTS recipients and return addresses are encoded as EBNF.822-address.
The MTS Originator is always encoded as MTS.OriginatorName, which maps onto MTS.ORAddressAndOptionalDirectoryName, which in turn maps onto MTS.ORName. 💅
4.6.1. RFC 822 -> X.400 📤
From the 822-MTS Originator, use the basic ORAddress mapping to generate MTS.PerMessageSubmissionFields.originator-name (MTS.ORName), without a DirectoryName.
For recipients, the following settings SHOULD be made for each component of MTS.PerRecipientMessageSubmissionFields.
- recipient-name: This SHOULD be derived from the 822-MTS recipient by the basic ORAddress mapping.
- originator-report-request: This SHOULD be set according to content return policy, as discussed in Section 5.2.
- explicit-conversion: This optional component SHOULD be omitted, as this service is not needed.
- extensions: The default value (no extensions) SHOULD be used. 🎀
4.6.2. X.400 -> RFC 822 📥
The basic functionality is to generate the 822-MTS originator and recipients. There is information present on the X.400 side which cannot be mapped into analogous 822-MTS services. For this reason, new RFC 822 fields are added for the MTS Originator and Recipients. The information discarded at the 822-MTS level SHOULD be present in these fields. There MAY also be the need to generate a delivery report. 🌈
4.6.2.1. 822-MTS Mappings
okay so, to build the 822-MTS originator (the return address), we use the basic ORAddress mapping on MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName) 💅 If MTS.ORName.directory-name is present, it should be discarded 🙈
The 822-MTS recipient is conceptually built from MTS.OtherMessageDeliveryFields.this-recipient-name. We take that field and run it through the basic ORAddress mapping to get an 822-MTS recipient, and we discard MTS.ORName.directory-name if it's there ✨ BUT, if we followed this model exactly, a message could never have more than one 822-MTS recipient. That's not okay at all 😭 so layering gets bent a little here. The mapping has to look at the MTA level info and map every MTA.PerRecipientMessageTransferFields.recipient-name where the responsibility bit is set onto an 822-MTS recipient 🦋
4.6.2.2. Generation of RFC 822 Headers
Not all of the per-recipient info can make it through at the 822-MTS level, so we make two brand new RFC 822 headers to carry it to the RFC 822 recipient 🎀 They're called X400-Originator: and X400-Recipients: 🧚
The X400-Originator: field should be set to the same value as the 822-MTS originator. Also, if MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName) contains MTS.ORName.directory-name, that Directory Name should be shown 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 through the X400-Recipients: field. Grabbing the recipients at the MTS level is what makes disclosure of recipients work properly, so it's giving correctness 👑 If any MTS.ORName.directory-name is present, it should be shown in an 822.comment. If MTS.OtherMessageDeliveryFields.orignally-intended-recipient-name is present, it should be shown in an associated 822.comment that starts with the string "Originally Intended Recipient" 🌸
Next, the following per-recipient services from MTS.OtherMessageDeliveryFields.extensions should be shown in comments if they're used. None of these services can be provided on RFC 822 networks, so in general these end up as informative strings attached to the other MTS recipients. Some of them have string values already defined. For the rest, the implementor can pick the string value. If the parameter has a default value, then no comment should be inserted ✨
requested-delivery-methodphysical-forwarding-prohibited:"(Physical Forwarding Prohibited)"physical-forwarding-address-request:"(Physical Forwarding Address Requested)"physical-delivery-modesregistered-mail-typerecipient-number-for-advicephysical-rendition-attributesphysical-delivery-report-request:"(Physical Delivery Report Requested)"proof-of-delivery-request:"(Proof of Delivery Requested)"
4.6.2.3. Delivery Report Generation
If MTA.PerRecipientMessageTransferFields.per-recipient-indicators requires a positive delivery notification, the gateway should generate it. Supplementary Information should be set to indicate that the report is gateway generated 🔥
4.6.3. Message IDs (MTS)
There's a mapping from 822.msg-id to MTS.MTSIdentifier 💖 The reverse mapping isn't needed, because MTS.MTSIdentifier always gets mapped onto new RFC 822 fields. The value of MTS.MTSIdentifier.local-part helps with correlating gateway errors 🕵️
To map from 822.msg-id, apply the standard mapping to 822.msg-id to generate an MTS.ORAddress. The Country, ADMD, and PRMD components of that 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), it should be truncated to that length 🥹
The reverse mapping isn't used in this specification. It would only be relevant where MTS.MTSIdentifier.local-identifier is of syntax 822.msg-id, and it algorithmically identifies MTS.MTSIdentifier 🧚♀️
4.7. IPMS Mappings
All RFC 822 addresses are assumed to use the 822.mailbox syntax. That includes all the 822.comments attached to the lexical tokens of the 822.mailbox 💅 In IPMS, O/R Names are encoded as MTS.ORName. This is used within the IPMS.ORDescriptor, IPMS.RecipientSpecifier, and IPMS.IPMIdentifier. There's an asymmetrical mapping between these components, so it's not a perfect mirror 🪞
4.7.1. RFC 822 -> X.400
Here we derive IPMS.ORDescriptor from an RFC 822 address 🦋
1. Take the address and extract an EBNF.822-address. You can get this trivially from either the 822.addr-spec or the 822.route-addr syntax. It's mapped to MTS.ORName as described above, and used as IMPS.ORDescriptor.formal-name 💜
2. Build a string that consists of (if present):
- The
822.phrasecomponent, if the822.addressis an822.phrase 822.route-addrconstruct. - Any
822.comments, in order, keeping 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, then IPMS.RecipientSpecifier.reply-request and IPMS.RecipientSpecifier.notification-requests should be set to their 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 an IPMS.ORDescriptor with only a free-form-name component should be built from it 🎀
4.7.2. X.400 -> RFC 822
This is the mapping from IPMS.ORDescriptor to an RFC 822 address. In the basic case, where IPMS.ORDescriptor.formal-name is present, follow these steps 🧚
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 it 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 that 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, it should be placed in an 822.comment with the string "Tel ". The normal international form of the number should be used. For example:
(Tel +44-1-387-7050)4. If IPMS.ORDescriptor.formal-name.directory-name is present, a text representation should be placed in a trailing 822.comment 💜
5. If IPMS.RecipientSpecifier.report-request has any non-default values, then the 822.comments "(Receipt Notification Requested)", and/or "(Non Receipt Notification Requested)", and/or "(IPM Return Requested)" should be appended to the address. Correlating P1 and P2 information is too much work to justify the gateway sending Receipt Notifications 😭
6. If IPMS.RecipientSpecifier.reply-request is True, an 822.comment "(Reply requested)" should be appended to the address ✨
If IPMS.ORDescriptor.formal-name is absent, IPMS.ORDescriptor.free-form-name should be converted to ASCII and used as 822.phrase within the RFC 822 822.group syntax. For example:
Free Form Name ":" ";"Steps 3-6 should then be followed 🌈
4.7.3. IP Message IDs
There's a need to map both ways between 822.msg-id and IPMS.IPMIdentifier 🫶 This lets X.400 Receipt Notifications, Replies, and Cross References refer to an RFC 822 Message ID, which is better than a gateway generated ID. A reversible and symmetrical mapping is defined, so good things happen when messages cross the X.400/RFC 822 boundary more than once 🔥
Message identifiers are tricky, because many systems use these IDs as uninterpreted keys, so they need to map to the exact form. Table-driven mappings aren't always symmetrical, especially with alternative domain names and alternative management domains. That's why a purely algorithmic mapping is used 🧠 This mapping can be simpler than the one for addresses, 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).
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. It's designed so the chance of clashes is low enough to be treated as impossible 🌟
4.7.3.1. 822.msg-id represented in X.400
IPMS.IPMIdentifier.user is omitted. 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 like this:
[ printablestring ] "*" [ std-or-address ]where EBNF.printablestring is the IPMS.IPMIdentifier.user-relative-identifier, and std-or-address is an encoding of the IPMS.IPMIdentifier.user. If necessary, the 822.quoted-string encoding is used. For example:
<"147*/S=Dietrich/O=Siemens/ADMD=DBP/C=DE/"@MHS>4.7.3.3. 822.msg-id -> IPMS.IPMIdentifier
If the 822.local-part can be parsed as:
[ printablestring ] "*" [ std-or-address ]and the 822.domain is "MHS", then this ID was X.400 generated 🎀 If EBNF.printablestring is present, its 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 that case, set IPMS.IPMIdentifier.user-relative-identifier to a printable string encoding of the 822.msg-id without the angle braces 🧚
4.7.3.4. IPMS.IPMIdentifier -> 822.msg-id
If IPMS.IPMIdentifier.user is absent, and IPMS.IPMIdentifier.user-relative-identifier, mapped to ASCII with angle braces added, parses as 822.msg-id, then this is an RFC 822 generated ID 🌸
Otherwise, the ID is X.400 generated. Use IPMS.IPMIdentifier.user to generate an EBNF.std-or-address form string. Build the 822.local-part of the 822.msg-id with this syntax:
[ printablestring ] "*" [ std-or-address ]The printablestring is taken from IPMS.IPMIdentifier.user-relative-identifier. Use 822.quoted-string if necessary. The 822.msg-id is generated with this 822.local-part and "MHS" as the 822.domain 💖
4.7.3.5. Phrase form 💅
okay so in Reply-To: and References:, you're allowed to use an 822.phrase instead of an 822.msg-id 🫶 To go from an 822.phrase to an IPMS.IPMIdentifier, you just put the phrase into IPMS.IPMIdentifier.user-relative-identifier 🎀 Going the other way for Reply-To: and References:: if IPMS.IPMIdentifier.user is absent AND the user-relative-identifier doesn't parse as an 822.msg-id, then you generate an 822.phrase instead of adding the domain MHS 🦋
4.7.3.6. RFC 987 backwards compatibility 🕰️
the mapping here is different from the one in RFC 987, because the RFC 987 mapping led to changed message IDs in a lot of cases 😭 fixing the problems is preferable to keeping backwards compatibility, no contest ✨ 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, so you'll see those everywhere 💅
5.1. RFC 822 -> X.400 💌
5.1.1. Basic Approach 🌸
a single IP Message gets generated 🎀 the RFC 822 headers are used to generate the IPMS.Heading, and the IP Message will have one IA5 IPMS.BodyPart containing the RFC 822 message body 💖
some RFC 822 fields can't be mapped onto a standard IPM Heading field, so an extended field is defined in Section 5.1.2 🦋 that's then used for fields which can't 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 aren't in principle available to the MTS User 🙈 using these services lets RFC 822 MTA level parameters get carried in the analogous X.400 service elements. the advantages of this mapping far outweigh the layering violation 👑
5.1.2. X.400 Extension Field 🧚
an IPMS Extension is defined:
rfc-822-field HEADING-EXTENSION
VALUE RFC822Field
::= id-rfc-822-field
RFC822Field ::= IA5Stringthe Object Identifier id-rfc-822-field is defined in Appendix D 🍓
to encode any RFC 822 Header using this extension, the RFC822Field should be set to the 822.field, omitting the trailing CRLF (e.g., Fruit-Of-The-Day: Kiwi Fruit) 🌈 structured fields should be unfolded. there should be no space before the ":". the reverse mapping builds the RFC 822 field in a straightforward manner 💅
5.1.3. Generating the IPM 📬
the IPM (IPMS Service Request) is generated according to the rules of this section 💜 the IPMS.IPM.body usually consists of one IPMS.BodyPart of type IPMS.IA5TextbodyPart, with IPMS.IA5TextBodyPart.parameters.repertoire set to the default (ia5), which contains the body of the RFC 822 message. the exception is where there is a Comments: field in the RFC 822 header 😭
if no specific 1988 features are used, the IPM 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. there are three options available at the IPM level, and using any of them conforms to this standard 🎀
- 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 🦋
- Reject any inbound message which would cause a message violating constraints to be generated. this will be robust, but may prevent useful communication 🫶
- 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), and 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:: ifSender: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 💅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 aReferences: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 stringComments:. 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., aDate:field with unparsable syntax) 💀
5.1.4. Mappings to the MTS Abstract Service 💌
the MTS.MessageSubmissionEnvelope comprises MTS.PerMessageSubmissionFields and 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 👑
MTS.PerMessageSubmissionFields.content-correlator should be encoded as IA5String, and contain the Subject:, Message-ID:, Date:, and To: fields (if present) 🌈 this should include the strings "Subject:", "Date:", "To:", "Message-ID:", and appropriate folding 💜 this should be truncated to MTS.ub-content-correlator-length (512) characters 😭 in addition, if there is a Subject: field, the MTS.PerMessageSubmissionFields.content-identifier should be set to a printable string representation of the contents of it, truncated to MTS.ub-content-id-length (16) 🙈 both are used, due to the much larger upper bound of the content correlator, and that the content id is available in X.400(1984) 🤔
5.1.5. Mappings to the MTA Abstract Service ✨
okay bestie, so we need to map straight onto some parts of the MTA Abstract Service, and here's why 💅
- so the MTS Message Identifier can be generated from the RFC 822
Message-ID:🆔 - so 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 🔁
here are the mappings we're defining 🎀
Message-Id: If this is present, 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 fromDate:MTA.DomainSuppliedInformation.routing-action: set torelayed
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 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 initial element of MTA.PerMessageTransferFields.trace-information will be generated already (from Date:) ✨
okay so 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 theReceived:lineMTA.MTASuppliedInformation.routing-action: set torelayed
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 GMTgenerates the string:
vs6.Cs.Ucl.AC.UK⚠️ bestie, read this part! Note that before transferring the message to some ADMDs, additional trace stripping may be required, as the implied path through multiple MDs would violate ADMD policy. 😭
two extended fields must be mapped, in order to prevent looping 🔥 "DL-Expansion-History:" is mapped to MTA.PerMessageTransferFields.extensions.dl-expansion-history. "Redirection-History:" is mapped to MTA.PerRecipientMessageTransferFields.extensions.redirection-history.
5.1.6. Mapping New Fields 🧚
this specification defines a number of new fields for Reports, Notifications and IP Messages in Section 5.3. As this specification only aims to preserve existing services, a gateway conforming to this specification does not need to map these fields to X.400, with the exception of "DL-Expansion-History" and "Redirection-History" described in the previous section. However, it is usually desirable and beneficial to do so, particularly to facilitate support of a message traversing multiple gateways. These mappings may be onto MTA, MTS, or IPMS services 💜
5.2. Return of Contents 📬
it is not clear how widely supported the X.400 return of contents service will be. Experience with X.400(1984) suggests that support of this service may not be universal. As this service is expected in the RFC 822 world, two approaches are specified. The choice will depend on the use of X.400 return of contents within 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 🙈
5.3. X.400 -> RFC 822 🦋
5.3.1. Basic Approach
a single RFC 822 message is generated from the incoming IP Message, Report, or IP Notification. All IPMS.BodyParts are mapped onto a single RFC 822 body. Other services are mapped onto RFC 822 header fields. Where there is no appropriate existing field, new fields are defined for IPMS, MTS and MTA services.
the gateway mechanisms will correspond to MTS Delivery. As with submission, there are aspects where the MTA (transfer) services are also used. In particular, there is an optimisation to allow for multiple 822-MTS recipients 💖
5.3.2. RFC 822 Settings 🎀
an RFC 822 Service requires to have a number of mandatory fields in the RFC 822 Header. Some 822-MTS services mandate specification of an 822-MTS Originator. Even in cases where this is optional, it is usually desirable to specify a value. The following defaults are defined, which should be used if the mappings specified do not derive a value:
- 822-MTS Originator: If this is not generated by the mapping (e.g., for a Delivery Report), a value pointing at a gateway administrator should be assigned.
Date:: A value will always be generated.From:: If this is not generated by the mapping, it should be assigned equal to the 822-MTS Originator. If this is gateway generated, an appropriate 822.phrase should be added.- At least one recipient field: If no recipient fields are generated, a field
"To: list:;"should be added.
this will ensure minimal RFC 822 compliance. When generating RFC 822 headers, folding should be used in an appropriate manner ✨
5.3.3. Basic Mappings 🌸
5.3.3.1. Encoded Information Types
this mapping from MTS.EncodedInformationTypes is needed in several disconnected places. EBNF is defined as follows:
encoded-info = 1#encoded-type
encoded-type = built-in-eit / object-identifier
built-in-eit = "Undefined" ; undefined (0)
/ "Telex" ; tLX (1)
/ "IA5-Text" ; iA5Text (2)
/ "G3-Fax" ; g3Fax (3)
/ "TIF0" ; tIF0 (4)
/ "Teletex" ; tTX (5)
/ "Videotex" ; videotex (6)
/ "Voice" ; voice (7)
/ "SFD" ; sFD (8)
/ "TIF1" ; tIF1 (9)MTS.EncodedInformationTypes is mapped onto EBNF.encoded-info. MTS.EncodedInformationTypes.non-basic-parameters is ignored. Built in types are mapped onto fixed strings (compatible with X.400(1984) and RFC 987), and other types are mapped onto EBNF.object-identifier 🧚
5.3.3.2. Global Domain Identifier
the following simple EBNF is used to represent MTS.GlobalDomainIdentifier:
global-id = std-or-addressthis is encoded using the std-or-address syntax, for the attributes within the Global Domain Identifier 💅
5.3.4. Mappings from the IP Message ✨
okay so bestie, first up: an IPM has to get mapped to RFC 822 🎀 The IPMS.IPM is made of an IPMS.IPM.heading and an IPMS.IPM.body, and we do the heading FIRST 💅 Some new fields get defined in EBNF (iykyk, it's giving formal 🧚):
ipms-field = "Obsoletes" ":" 1#msg-id
/ "Expiry-Date" ":" date-time
/ "Reply-By" ":" date-time
/ "Importance" ":" importance
/ "Sensitivity" ":" sensitivity
/ "Autoforwarded" ":" boolean
/ "Incomplete-Copy" ":"
/ "Language" ":" language
/ "Message-Type" ":" message-type
/ "Discarded-X400-IPMS-Extensions" ":" 1#oid
importance = "low" / "normal" / "high"
sensitivity = "Personal" / "Private" /
"Company-Confidential"
language = 2*ALPHA [ language-description ]
language-description = printable-string
message-type = "Delivery Report"
/ "InterPersonal Notification"
/ "Multiple Part"The mappings and actions for the IPMS.Heading get specified for each element 🦋 Addresses and Message Identifiers are mapped according to Chapter 4, and the other mappings are either explained or straightforward (algorithmic) ✨ Here's the tea:
IPMS.Heading.this-IPM: mapped toMessage-ID:🌸IPMS.Heading.originator: if IPMS.Heading.authorizing-users is present this goes toSender:, and if not, toFrom:👑IPMS.Heading.authorizing-users: mapped toFrom:💜IPMS.Heading.primary-recipients: mapped toTo:🍓IPMS.Heading.copy-recipients: mapped toCc:🫶IPMS.Heading.blind-copy-recipients: mapped toBcc:🙈IPMS.Heading.replied-to-ipm: mapped toIn-Reply-To:🔥IPMS.Heading.obsoleted-IPMs: mapped to the extended RFC 822 fieldObsoletes:⭐IPMS.Heading.related-IPMs: mapped toReferences:🦋IPMS.Heading.subject: mapped toSubject:. The contents are converted to ASCII (as defined in Chapter 3). Any CRLF are NOT mapped, but they're used as points where the subject field must be folded 🌈IPMS.Heading.expiry-time: mapped to the extended RFC 822 fieldExpiry-Date:⏰IPMS.Heading.reply-time: mapped to the extended RFC 822 fieldReply-By:🧚IPMS.Heading.reply-recipients: mapped toReply-To:💅IPMS.Heading.importance: mapped to the extended RFC 822 fieldImportance:🔥IPMS.Heading.sensitivity: mapped to the extended RFC 822 fieldSensitivity:🎀IPMS.Heading.autoforwarded: mapped to the extended RFC 822 fieldAutoforwarded:💖
The standard extensions (Annex H of X.420 / ISO 10021-7) are mapped like this, no cap 🧁
incomplete-copy: mapped to the extended RFC 822 fieldIncomplete-Copy:🌸language: mapped to the extended RFC 822 fieldLanguage:, 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, it should be mapped onto an RFC 822 header, as described in Section 5.1.2 📜
If a non-standard extension shows up, it should be discarded, UNLESS the gateway understands the extension and can perform an appropriate mapping onto an RFC 822 header field. If extensions get discarded, the list should be indicated in the extended RFC 822 field Discarded-X400-IPMS-Extensions: 🚨
The IPMS.Body gets mapped into the RFC 822 message body 🫧 Each IPMS.BodyPart gets converted to ASCII like so:
IPMS.IA5Text: the mapping is straightforward (see Chapter 3) ✨IPMS.MessageBodyPart: the X.400 -> RFC 822 mapping should be applied recursively, 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 fieldDelivery-Date:🎁Other: if other body parts can be mapped to IA5, either by using 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 can't be converted, there are three options, and ALL of them conform to this standard 🙌 A different choice may be made for the case where NO body part can be converted:
- The first option is to reject the message and send a non-delivery notification. This must always be done if conversion is prohibited. 🚫
- The second option is to map a missing body part to something of the style below. This will let some useful information get transferred. As the recipient is a human (IPMS), suitable action should be available 💌
*********************************
There was a foobar here
The widget gateway ate it
*********************************- Finally, both can be done. In this case, the supplementary information in the (positive) Delivery Report should make clear that something was sent on to the recipient with substantial loss of information 💀
Where there's more than one IPMS.BodyPart, the mapping defined by Rose and Stefferud in [Rose85a] should be used to map the separate IPMS.BodyParts into the single RFC 822 message body 🌈 If this is done, a Message-Type: field with value Multiple part should be added, which tells a receiving gateway that the message may be unfolded according to RFC 934 🧩
And for backwards compatibility with RFC 987, these procedures should also be followed 🕰️ If there are two IA5 body parts, and the first starts with the string RFC-822-Headers: as its first line, then the remainder of this body part should be appended to the RFC 822 header 🎀
5.3.5. Mappings from an IP Notification
okay now the notifications 🔔 A message gets generated, with these 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 exists so that ALL the info from an interpersonal notification is available to the end user in a uniform way 🫶
ipn-body-format = ipn-description <CRLF>
[ ipn-extra-information <CRLF> ]
ipn-content-return
ipn-description = ipn-receipt / ipn-non-receipt
ipn-receipt = "Your message to:" preferred-recipient <CRLF>
"was received at" receipt-time <CRLF> <CRLF>
"This notification was generated"
acknowledgement-mode <CRLF>
"The following extra information was given:" <CRLF>
ipn-suppl <CRLF>
ipn-non-receipt "Your message to:"
preferred-recipient <CRLF>
ipn-reason
ipn-reason = ipn-discarded / ipn-auto-forwarded
ipn-discarded = "was discarded for the following reason:"
discard-reason <CRLF>
ipn-auto-forwarded = "was automatically forwarded." <CRLF>
[ "The following comment was made:"
auto-comment ]
ipn-extra-information =
"The following information types were converted:"
encoded-info
ipn-content-return = "The Original Message is not available"
/ "The Original Message follows:"
<CRLF> <CRLF> message
preferred-recipient = mailbox
receipt-time = date-time
auto-comment = printablestring
ipn-suppl = printablestring
non-receipt-reason = "Discarded" / "Auto-Forwarded"
discard-reason = "Expired" / "Obsoleted" /
"User Subscription Terminated"
acknowledgement-mode = "Manually" / "Automatically"The mappings for the elements of the common fields of IPMS.IPN (IPMS.CommonFields) onto this structure and the message header are 🧠
subject-ipm: mapped toReferences:🦋ipm-originator: mapped toTo:💌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 looks like this, and it's so cute 🥹
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
Your message to: Steve Kille <steve@cs.ucl.ac.uk>
was automatically forwarded.
The following comment was made:
Sent on to a random destination
The following information types were converted: g3fax
The Original Message is not available5.3.6. Mappings from the MTS Abstract Service ✨
okay bestie, this part is all about the MTS mappings for User Messages (IPM and IPN) 💌 the whole thing works by mapping MTS.MessageDeliveryEnvelope, and to make it work we add a bunch of extended RFC 822 fields. here's the grammar 🎀
mts-field = "X400-MTS-Identifier" ":" mts-msg-id
/ "X400-Originator" ":" mailbox
/ "X400-Recipients" ":" 1#mailbox
/ "Original-Encoded-Information-Types" ":"
encoded-info
/ "X400-Content-Type" ":" mts-content-type
/ "Content-Identifier" ":" printablestring
/ "Priority" ":" priority
/ "Originator-Return-Address" ":" 1#mailbox
/ "DL-Expansion-History" ":" mailbox ";" date-time ";"
/ "Redirection-History" ":" redirection
/ "Conversion" ":" prohibition
/ "Conversion-With-Loss" ":" prohibition
/ "Requested-Delivery-Method" ":"
1*( labelled-integer )
/ "Delivery-Date" ":" date-time
/ "Discarded-X400-MTS-Extensions" ":"
1#( oid / labelled-integer )
prohibition = "Prohibited" / "Allowed"
mts-msg-id = "[" global-id ";" *text "]"
mts-content-type = "P2" / labelled-integer
/ object-identifer
priority = "normal" / "non-urgent" / "urgent"
redirection = mailbox ";" "reason" "="
redirection-reason
";" date-time
redirection-reason =
"Recipient Assigned Alternate Recipient"
/ "Originator Requested Alternate Recipient"
/ "Recipient MD Assigned Alternate Recipient"okay so now let's go element by element 🫶
MTS.MessageDeliveryEnvelope.message-delivery-identifiergets mapped to the extended RFC 822 fieldX400-MTS-Identifier:✨MTS.MessageDeliveryEnvelope.message-delivery-timeis discarded, because this time gets represented in an appropriate trace element 🕰️
the mappings for the elements of MTS.MessageDeliveryEnvelope.other-fields (MTS.OtherMessageDeliveryFields) are next 💅
content-typegets mapped to the extended RFC 822 fieldX400-Content-Type:. the stringP2is there for backwards compatibility with RFC 987 🎀. if the content type is 22, then a labelled-integer encoding should be used 🔥originator-namegets mapped to the 822-MTS originator, and also to the extended RFC 822 fieldX400-Originator:. this is described in Section 4.6.2 💖original-encoded-information-typesgets mapped to the extended RFC 822 fieldOriginal-Encoded-Information-Types:🦋prioritygets mapped to the extended RFC 822 fieldPriority:👑delivery-flags: if the conversion-prohibited bit is set, add an extended RFC 822 fieldConversion:🌸this-recipient-nameandother-recipient-namesget used together to generate the extended RFC 822 fieldX400-Recipients:. ngl the latter will only show up if disclosure of recipients is allowed 🙈originally-intended-recipient-namegets mapped to a comment associated with the recipient in question, as described in Section 4.6.2.2 🧚converted-encoded-information-typesis discarded, since it will always be IA5 only 💀message-submission-timegets mapped toDate:🍓content-identifiergets mapped to the extended RFC 822 fieldContent-Identifier:💜
if any extensions (MTS.MessageDeliveryEnvelope.other-fields.extensions) are present, and they're marked as critical for transfer or delivery, then the message should be rejected 😭. otherwise, the extensions get mapped like this:
conversion-with-loss-prohibited: if it's set toMTS.ConversionWithLossProhibited.conversion-with-loss-prohibited, then add the extended RFC 822 fieldConversion-With-Loss:🌈requested-delivery-methodgets mapped to the extended RFC 822 fieldRequested-Delivery-Method:🫧originator-return-addressgets mapped to the extended RFC 822 fieldOriginator-Return-Address:💅
these ones are only appropriate for physical delivery, so they show up as comments in the X400-Recipients: field, as described in Section 4.6.2.2 🎀:
physical-forwarding-address-requestphysical-delivery-modesregistered-mail-typerecipient-number-for-advicephysical-rendition-attributesphysical-delivery-report-requestphysical-forwarding-prohibited
this next group implies security services that the RFC 822 environment just doesn't have 🔐. if they're marked as critical for transfer or delivery, the message should be rejected. otherwise they should be discarded 💀
originator-certificatemessage-tokencontent-confidentiality-algorithm-identifiercontent-integrity-checkmessage-origin-authentication-checkmessage-security-labelproof-of-delivery-request
and then the history fields 🕰️
redirection-history: each element gets mapped to an extended RFC 822 fieldRedirection-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 gets mapped to the extended RFC 822 fieldDL-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 that aren't specified in X.400 are present, and they're marked as critical for transfer or delivery, then the message should be rejected. if they're not marked that way, they can safely be discarded. the list of discarded fields should be indicated in the extended header Discarded-X400-MTS-Extensions: 💅
5.3.7. Mappings from the MTA Abstract Service 🌷
there are some mappings at the MTA Abstract Service level that get done for IPM and IPN too 🧚 these can be derived from MTA.MessageTransferEnvelope. so why do we violate layering like this? ngl it's for three reasons 👑
- allowing 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. that's 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 that's because of differing service requests for each recipient, then a different message should be generated 🔥. but if it's only due to the request for non-disclosure of recipients, then the X400-Recipients: field should be omitted, and only one message sent 🙈
the following EBNF is defined for extended RFC 822 headers 🎀
mta-field = "X400-Received" ":" x400-trace
/ "Deferred-Delivery" ":" date-time
/ "Latest-Delivery-Time" ":" date-time
x400-trace = "by" md-and-mta ";"
[ "deferred until" date-time ";" ]
[ "converted" "(" encoded-info ")" ";" ]
[ "attempted" md-and-mta ";" ]
action-list
";" arrival-time
md-and-mta = [ "mta" mta "in" ] global-id
mta = word
arrival-time = date-time
action-list = 1#action
action = "Redirected"
/ "Expanded"
/ "Relayed"
/ "Rerouted"if MTA.PerMessageTransferFields.deferred-delivery-time is present, use it to generate a Deferred-Delivery: field 🕰️. X.400 doesn't make this info available at the MTS level on delivery, which is kinda wild, but okay 😭. 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 isn't, the function may optionally be implemented by the gateway: that means the gateway should hold the message until the time specified in the protocol element 🦋. so 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 hasn't been stripped, this may take some complex interleaving 🙈. use that list to generate a sequence of X400-Received: fields. the only difference between external trace and internal trace is the 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) looks like this:
X400-Received: by /PRMD=UK.AC/ADMD=Gold 400/C=GB/ ; Relayed ;
Tue, 20 Jun 89 19:25:11 +0100and a more complex example (internal) looks like this 🍓:
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 +01005.3.8. Mappings from Report Delivery 📬
delivery reports get mapped at the MTS service level 💌. that means only reports destined for the MTS user will be mapped 🫶. some additional services are also taken from the MTA service too 🌸
5.3.8.1. MTS Mappings 📬
okay so a Delivery Report service gets represented as MTS.ReportDeliveryEnvelope 💌, which is made up of per-report-fields (MTS.PerReportDeliveryFields) and per-recipient-fields.
a message should be generated with these 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 body format is locked in so every RFC 822 user gets the info the same way every time 🫶. it starts with a summary of the critical stuff, then a full listing of all the parameters:
dr-body-format = dr-summary <CRLF>
dr-recipients <CRLF>
dr-extra-information <CRLF>
dr-content-return
dr-content-return = "The Original Message is not available"
/ "The Original Message follows:"
<CRLF> <CRLF> message
dr-summary = "This report relates to your message:" <CRLF>
content-correlator <CRLF> <CRLF>
"of" date-time <CRLF> <CRLF>
"It was generated by:" report-point <CRLF>
"at" date-time <CRLF> <CRLF>
"It was later converted to RFC 822 by:" mailbox <CRLF>
"at" date-time <CRLF> <CRLF>
dr-recipients = *(dr-recipient <CRLF> <CRLF>)
dr-recipient = dr-recip-success / dr-recip-failure
dr-recip-success =
"Your message was successfully delivered to:"
mailbox "at" date-time
dr-recip-failure = "Your message was not delivered to:"
mailbox <CRLF>
"for the following reason:" *word
dr-extra-information =
"-----------------------------------------------" <CRLF> <CRLF>
"The following information is derived from the Report" <CRLF>
"It may be useful for problem diagnosis:" <CRLF> <CRLF>
drc-field-list
drc-field-list = *(drc-field <CRLF>)
drc-field = "Subject-Submission-Identifier" ":"
mts-msg-id
/ "Content-Identifier" ":" printablestring
/ "Content-Type" ":" mts-content-type
/ "Original-Encoded-Information-Types" ":"
encoded-info
/ "Originator-and-DL-Expansion-History" ":"
dl-history
/ "Reporting-DL-Name" ":" mailbox
/ "Content-Correlator" ":" content-correlator
/ "Recipient-Info" ":" recipient-info
/ "Subject-Intermediate-Trace-Information" ":"
x400-trace
recipient-info = mailbox "," std-or ";"
report-type
[ "converted eits" encoded-info ";" ]
[ "originally intended recipient"
mailbox "," std-or ";" ]
[ "last trace" [ encoded-info ] date-time ";" ]
[ "supplementary info" <"> printablestring <"> ";" ]
[ "redirection history" 1#redirection ";"
[ "physical forwarding address"
printablestring ";" ]
report-type = "SUCCESS" drc-success
/ "FAILURE" drc-failure
drc-success = "delivered at" date-time ";"
[ "type of MTS user" labelled-integer ";" ]
drc-failure = "reason" labelled-integer ";"
[ "diagnostic" labelled-integer ";" ]
report-point = [ "mta" word "in" ] global-id
content-correlator = *word
dl-history = 1#( mailbox "(" date-time ")")the format is a fixed definition, no freestyling 🙅♀️. the only exception is that EBNF.drc-fields should follow RFC 822 folding rules.
the elements of MTS.ReportDeliveryEnvelope.per-report-fields get mapped onto extended RFC 822 fields like this 🧚:
subject-submission-identifierMapped to EBNF.drc-field (Subject-Submission-Identifier)content-identifierMapped to EBNF.drc-field (Content-Identifier)content-typeMapped to EBNF.drc-field (Content-Type)original-encoded-information-typesMapped to EBNF.drc-field (Encoded-Info)
and the extensions from MTS.ReportDeliveryEnvelope.per-report-fields.extensions get mapped like so:
originator-and-DL-expansion-historyMapped to EBNF.drc-field (Originator-and-DL-Expansion-History)reporting-DL-nameMapped to EBNF.drc-field (Reporting-DL-Name)content-correlatorMapped to EBNF.content-correlator, provided that the encoding is IA5String (this should always be the case). This gets 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 ✨.
the security parameters are the one place where we go easy on the data 🔐:
message-security-label,reporting-MTA-certificate,report-origin-authentication-check
these security parameters should not be present. If they are, they should be discarded in preference to discarding the whole report. so we toss the security bits, not the entire 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 get mapped like this:
actual-recipient-nameUsed to generate the first EBNF.mailbox and EBNF.std-or in EBNF.recipient-info. Both RFC 822 and X.400 forms are given, since 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.reportIf 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 interpretation of the reason and diagnostic codes, and including any supplementary information. EBNF.drc-failure should be filled in systematically.converted-encoded-information-typesSet EBNF.drc-field ("converted eits")originally-intended-recipientSet the second ("originally intended recipient") mailbox and std-or in EBNF.drc-field.supplementary-infoSet EBNF.drc-field ("supplementary info"), and include this information in EBNF.dr-recip-failure.redirection-historySet EBNF.drc-field ("redirection history")physical-forwarding-addressSet ENBF.drc-field ("physical forwarding address")recipient-certificateDiscardproof-of-deliveryDiscard
any unknown extensions should be discarded, irrespective of criticality 🗑️.
the original message should be included in the delivery port 📨. it'll usually be available at the gateway, as discussed in Section 5.2.
5.3.8.2. MTA Mappings 🌸
the single 822-MTS recipient is built from MTA.ReportTransferEnvelope.report-destination-name, using the mappings of Chapter 4. Unlike with a user message, this info isn't available at the MTS level, so it's a little different 🙃.
the following additional mappings should be made:
MTA.ReportTransferEnvelope.report-destination-nameThis should be used to generate the To: field.MTA.ReportTransferEnvelope.identifierMapped to the extended RFC 822 field "X400-MTS-Identifier:". It may also be used to derive a "Message-Id:" field.MTA.ReportTransferEnvelope.trace-informationandMTA.ReportTransferEnvelope.internal-trace-informationMapped 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-informationMapped to EBNF.recipient-info (last trace)MTA.PerReportTransferFields.subject-intermediate-trace-informationMapped to EBNF.drc-field (subject-Intermediate-Trace-Information). These fields should be ordered so that the most recent trace element comes first 🕰️.
5.3.8.3. Example Delivery Report 💖
this is an example of a moderately complex report, so buckle up 🎀.
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)
-----------------------------------------------
The following information is derived from the Report
It may be useful for problem diagnosis:
Subject-Submission-Identifier:
[/PRMD=UK.AC/ADMD=Gold 400/C=GB/;148996]
Content-Identifier: X.400 Delivery Report
Content-Type: P2-1988 (22)
Original-Encoded-Information-Types: ia5
Content-Correlator: Date: Wed, 21 Jun 89 06:15:43 +0000
Message-ID: <8907140715.aa09015@CS.Nott.AC.UK>
Subject: Now it's the fine tuning .... !
To: Piete Brooks (Postmaster) <pb@computer-lab.cambridge.ac.uk>
Recipient-Info:
bad-user@nowhere, /S=bad-user/PRMD=nowhere/ADMD=DBP/C=DE/ ;
FAILURE reason Physical-Rendition-Not-Performed (3) ;
diagnostic Punctuation-Symbol-Loss (23) ;
supplementary info Umlaut failure
The Original Message follows:
Subject: Now it's the fine tuning .... !
Date: Wed, 21 Jun 89 06:15:43 +0000
From: Julian Onions <jpo@computer-science.nottingham.ac.uk>
To: Piete Brooks (Postmaster) <pb@computer-lab.cambridge.ac.uk>
Cc: bad-user@nowhere
Message-ID: <8907140715.aa09015@CS.Nott.AC.UK>
A short test5.3.9. Probe 🔍
this is an MTS internal issue 🛠️. any probe should be serviced by the gateway, since there's no equivalent RFC 822 functionality. the value of the reply depends on whether the gateway could service an MTS Message with the values specified in the probe. the reply should make use of MTS.SupplementaryInformation to indicate that the probe was serviced by the gateway.
Appendix A - Differences with RFC 987 🦋
this appendix sums up the changes between this doc and RFC 987/RFC 1026.
1. Introduction ✨
the model has shifted from a protocol based mapping to a service based mapping. this has increased the generality of the specification and improved the model, and the change affects the entire document 🌈.
a restriction on scope has been added.
2. Service Elements 💅
- the new service elements of X.400 are dealt with.
- a clear distinction is made between origination and reception.
3. Basic Mappings 🎀
- add teletex support.
- add object identifier support.
- add labelled integer support.
- make
PrintableString <-> ASCIImapping reversible. - the printable string mapping is aligned to the NBS mapping derived from RFC 987.
4. Addressing 💖
Okay so this part is the addressing glow-up 🎀 and it's giving "new and improved":
- Support for new addressing attributes. 💅
- The message ID mapping is changed to not be table driven. 🔥
5. Detailed Mappings ✨
This section is basically the big list of everything that got reworked, and honestly the vibes are immaculate 😭
- Define extended IPM Header, and use instead of second body part for RFC 822 extensions. 🦋
- Realignment of element names. 🌸
- New syntax for reports, simplifying the header and introducing a mandatory body format (the RFC 987 header format was unusable). 💀 Like, the old one was genuinely cursed, so we're not mourning it.
- Drop complex autoforwarded mapping. 🙈
- Add full mapping for IP Notifications, defining a body format. 🫶
- Adopt an MTS Identifier syntax in line with the O/R Address syntax. 💜
- A new format for X400 Trace representation on the RFC 822 side. 🧚
6. Appendices 🌈
The appendices got a little reshuffle too, and I'm here for it:
- Move Appendix on restricted 822 mappings to a separate RFC. 🍓
- Delete Phonenet and SMTP Appendixes. 👋
Appendix B - Mappings specific to the JNT Mail 🎀
This appendix is specific to the JNT Mail Protocol, so it's the extra-special stuff for that protocol. It describes the specific changes in the context of that protocol. 💖
1. Introduction
There are five aspects of a gateway which are JNT Mail Specific. Each one gets its own section of this appendix, so let's go 🫶
2. Domain Ordering
When interpreting and generating domains, the UK NRS domain ordering must be used. 🇬🇧✨
3. Acknowledge-To:
Okay so this field doesn't have a direct buddy in X.400 🥲 but it can be supported to an extent, and it can help improve X.400 support. Iconic glow-up energy.
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:
- Acknowledgement(s) should be generated by the gateway. The text of these acknowledgements should indicate that they are generated by the gateway. 💅
- 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.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. 🙈 Not gonna lie, this one is a little tricky, but it makes sense once you see the whole picture.
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
Okay, this is the drama 😭 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 fix that, a new extended JNT Mail field is defined. It's chosen to line up with the JNT recommendation for interworking with full RFC 822 systems [Kille84b].
original-sender = "Original-Sender" ":" mailboxIf 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, then MTS.OtherMessageDeliveryFields.originator-name should be mapped onto the Sender: field, and IPMS.Heading.originator mapped onto the Original-Sender: field.
In other cases the MTS.OtherMessageDeliveryFields.originator-name is already correctly represented. ✨
Appendix C - Mappings specific to UUCP Mail 🧚
Gatewaying of UUCP and X.400 is handled by first gatewaying the UUCP address into RFC 822 syntax (using RFC 976) and then gatewaying the resulting RFC 822 address into X.400. For example, an X.400 address:
Country US
Organisation Xerox
Personal Name John Smithmight be expressed from UUCP as
inthop!gate!gatehost.COM!/C=US/O=Xerox/PN=John.Smith/(assuming gate is a UUCP-Internet gateway and gatehost.COM is an Internet-X.400 gateway) or
inthop!gate!Xerox.COM!John.Smith(assuming that Xerox.COM and /C=US/O=Xerox/ are equivalent.)
In the other direction, a UUCP address Smith@ATT.COM, integrated into 822, would be handled as any other 822 address. A non-integrated address such as inthop!dest!user might be handled through a pair of gateways:
Country US
ADMD ATT
PRMD Internet
Organisation GateOrg
RFC-822 inthop!dest!user@gatehost.COMor through a single X.400 to UUCP gateway:
Country US
ADMD ATT
PRMD UUCP
Organisation GateOrg
RFC-822 inthop!dest!userAppendix D - Object Identifier Assignment 👑
An object identifier is needed for the extension IPMS element. The following value should be used.
rfc-987-88 OBJECT IDENTIFIER ::=
{ccitt data(9) pss(2342) ucl(234219200300) rfc-987-88(200)}
id-rfc-822-field OBJECT IDENTIFIER ::= {rfc987-88 field(0)}Appendix E - BNF Summary 🧚✨
Okay bestie, this is the grammar cheat sheet 💅 Every piece of syntax from the whole doc gets its little BNF recipe here, so you can check any weird-looking bit against the exact rules. Let's gooo 🎀
Here's the basic stuff: the boolean, the numeric strings, and the printable strings 🌸
boolean = "TRUE" / "FALSE"
numericstring = *DIGIT
printablestring = *( ps-char )
ps-restricted-char = 1DIGIT / 1ALPHA / " " / "'" / "+"
/ "," / "-" / "." / "/" / ":" / "=" / "?"
ps-delim = "(" / ")"
ps-char = ps-delim / ps-restricted-char
ps-encoded = *( ps-restricted-char / ps-encoded-char )
ps-encoded-char = "(a)" ; (@)
/ "(p)" ; (%)
/ "(b)" ; (!)
/ "(q)" ; (")
/ "(u)" ; (_)
/ "(l)" ; "("
/ "(r)" ; ")"
/ "(" 3DIGIT ")"
teletex-string = *( ps-char / t61-encoded )
t61-encoded = "{" 1* t61-encoded-char "}"
t61-encoded-char = 3DIGIT
teletex-and-or-ps = [ printablestring ] [ "*" teletex-string ]Next up are the labelled integers and the object identifiers. These two have such a main character energy 👑
labelled-integer ::= [ key-string ] "(" numericstring ")"
key-string = *key-char
key-char = <a-z, A-Z, 1-9, and "-">
object-identifier ::= [ defined-value ] oid-comp-list
oid-comp-list ::= oid-comp oid-comp-list
| oid-comp
defined-value ::= key-string
oid-comp ::= [ key-string ] "(" numericstring ")"Now the encoded information types. The built-in list is giving a whole catalogue 🦋
encoded-info = 1#encoded-type
encoded-type = built-in-eit / object-identifier
built-in-eit = "Undefined" ; undefined (0)
/ "Telex" ; tLX (1)
/ "IA5-Text" ; iA5Text (2)
/ "G3-Fax" ; g3Fax (3)
/ "TIF0" ; tIF0 (4)
/ "Teletex" ; tTX (5)
/ "Videotex" ; videotex (6)
/ "Voice" ; voice (7)
/ "SFD" ; sFD (8)
/ "TIF1" ; tIF1 (9)Here's the personal name grammar 🙈 It's all about given names, initials, and surnames.
encoded-pn = [ given "." ] *( initial "." ) surname
given = 2*<ps-char not including ".">
initial = ALPHA
surname = printablestringNext is the standard O/R address stuff, with its attributes and values all in a row 💜
std-or-address = 1*( "/" attribute "=" value ) "/"
attribute = standard-type
/ "RFC-822"
/ registered-dd-type
/ dd-key "." std-printablestring
standard-type = key-string
registered-dd-type
= key-string
dd-key = key-string
value = std-printablestring
std-printablestring
= *( std-char / std-pair )
std-char = <"{", "}", "*", and any ps-char
except "/" and "=">
std-pair = "$" ps-charThen the domain-defined O/R address. Super structured, super iconic 🌈
dmn-or-address = dmn-part *( "." dmn-part )
dmn-part = attribute "$" value
attribute = standard-type
/ "~" dmn-printablestring
value = dmn-printablestring
/ "@"
dmn-printablestring =
= *( dmn-char / dmn-pair )
dmn-char = <"{", "}", "*", and any ps-char
except ".">
dmn-pair = "."
global-id = std-or-addressNow the MTA trace fields, which is where the X.400 history gets logged 🍓
mta-field = "X400-Received" ":" x400-trace
/ "Deferred-Delivery" ":" date-time
/ "Latest-Delivery-Time" ":" date-time
x400-trace = "by" md-and-mta ";"
[ "deferred until" date-time ";" ]
[ "converted" "(" encoded-info ")" ";" ]
[ "attempted" md-and-mta ";" ]
action-list
";" arrival-time
md-and-mta = [ "mta" mta "in" ] global-id
mta = word
arrival-time = date-time
action-list = 1#action
action = "Redirected"
/ "Expanded"
/ "Relayed"
/ "Rerouted"Next are the delivery report grammars. Okay this part is a lot, but it's so organised, I'm obsessed 😭
dr-body-format = dr-summary <CRLF>
dr-recipients <CRLF>
dr-extra-information <CRLF>
dr-content-return
dr-content-return = "The Original Message is not available"
/ "The Original Message follows:"
<CRLF> <CRLF> message
dr-summary = "This report relates to your message:" <CRLF>
content-correlator <CRLF> <CRLF>
"of" date-time <CRLF> <CRLF>
"It was generated by:" report-point <CRLF>
"at" date-time <CRLF> <CRLF>
"It was later converted to RFC 822 by:" mailbox <CRLF>
"at" date-time <CRLF> <CRLF>
dr-recipients = *(dr-recipient <CRLF> <CRLF>)
dr-recipient = dr-recip-success / dr-recip-failure
dr-recip-success =
"Your message was successfully delivered to:"
mailbox "at" date-time
dr-recip-failure = "Your message was not delivered to:"
mailbox <CRLF>
"for the following reason:" *word
dr-extra-information =
"-----------------------------------------------" <CRLF> <CRLF>
"The following information is derived from the Report" <CRLF>
"It may be useful for problem diagnosis:" <CRLF> <CRLF>
drc-field-list
drc-field-list = *(drc-field <CRLF>)
drc-field = "Subject-Submission-Identifier" ":"
mts-msg-id
/ "Content-Identifier" ":" printablestring
/ "Content-Type" ":" mts-content-type
/ "Original-Encoded-Information-Types" ":"
encoded-info
/ "Originator-and-DL-Expansion-History" ":"
dl-history
/ "Reporting-DL-Name" ":" mailbox
/ "Content-Correlator" ":" content-correlator
/ "Recipient-Info" ":" recipient-info
recipient-info = mailbox "," std-or ";"
report-type
[ "converted eits" encoded-info ";" ]
[ "originally intended recipient"
mailbox "," std-or ";" ]
[ "supplementary info" <"> printablestring <"> ";" ]
[ "redirection history" 1#redirection ";"
[ "physical forwarding address"
printablestring ";" ]
report-type = "SUCCESS" drc-success
/ "FAILURE" drc-failure
drc-success = "delivered at" date-time ";"
[ "type of MTS user" labelled-integer ";" ]
drc-failure = "reason" labelled-integer ";"
[ "diagnostic" labelled-integer ";" ]
report-point = [ "mta" word "in" ] global-id
content-correlator = *word
dl-history = 1#( mailbox "(" date-time ")")Next up is the MTS field grammar, with all the envelope bits 💖
mts-field = "X400-MTS-Identifier" ":" mts-msg-id
/ "X400-Originator" ":" mailbox
/ "X400-Recipients" ":" 1#mailbox
/ "Original-Encoded-Information-Types" ":"
encoded-info
/ "X400-Content-Type" ":" mts-content-type
/ "Content-Identifier" ":" printablestring
/ "Priority" ":" priority
/ "Originator-Return-Address" ":" 1#mailbox
/ "DL-Expansion-History" ":" mailbox ";" date-time ";"
/ "Redirection-History" ":" redirection
/ "Conversion" ":" prohibition
/ "Conversion-With-Loss" ":" prohibition
/ "Requested-Delivery-Method" ":"
1*( labelled-integer )
/ "Delivery-Date" ":" date-time
/ "Discarded-X400-MTS-Extensions" ":"
1#( oid / labelled-integer )
prohibition = "Prohibited" / "Allowed"
mts-msg-id = "[" global-id ";" *text "]"
mts-content-type = "P2" / labelled-integer
/ object-identifer
priority = "normal" / "non-urgent" / "urgent"
redirection = mailbox ";" "reason" "="
redirection-reason
";" date-time
redirection-reason =
"Recipient Assigned Alternate Recipient"
/ "Originator Requested Alternate Recipient"
/ "Recipient MD Assigned Alternate Recipient"Last bit is the IPN (interpersonal notification) grammar, which has its own vibe 🦋
ipn-body-format = ipn-description <CRLF>
[ ipn-extra-information <CRLF> ]
ipn-content-return
ipn-description = ipn-receipt / ipn-non-receipt
ipn-receipt = "Your message to:" preferred-recipient <CRLF>
"was received at" receipt-time <CRLF> <CRLF>
"This notification was generated"
acknowledgement-mode <CRLF>
"The following extra information was given:" <CRLF>
ipn-suppl <CRLF>
ipn-non-receipt "Your message to:"
preferred-recipient <CRLF>
ipn-reason
ipn-reason = ipn-discarded / ipn-auto-forwarded
ipn-discarded = "was discarded for the following reason:"
discard-reason <CRLF>
ipn-auto-forwarded = "was automatically forwarded." <CRLF>
[ "The following comment was made:"
auto-comment ]
ipn-extra-information =
"The following information types were converted:"
encoded-info
ipn-content-return = "The Original Message is not available"
/ "The Original Message follows:"
<CRLF> <CRLF> message
preferred-recipient = mailbox
receipt-time = date-time
auto-comment = printablestring
ipn-suppl = printablestring
non-receipt-reason = "Discarded" / "Auto-Forwarded"
discard-reason = "Expired" / "Obsoleted" /
"User Subscription Terminated"
acknowledgement-mode = "Manually" / "Automatically"And finally the message status (MS) fields and the message types 🎀✨
ms-field = "Obsoletes" ":" 1#msg-id
/ "Expiry-Date" ":" date-time
/ "Reply-By" ":" date-time
/ "Importance" ":" importance
/ "Sensitivity" ":" sensitivity
/ "Autoforwarded" ":" boolean
/ "Incomplete-Copy" ":"
/ "Language" ":" language
/ "Message-Type" ":" message-type
/ "Discarded-X400-IPMS-Extensions" ":" 1#oid
importance = "low" / "normal" / "high"
sensitivity = "Personal" / "Private" /
"Company-Confidential"
language = 2*ALPHA [ language-description ]
language-description = printable-string
message-type = "Delivery Report"
/ "InterPersonal Notification"
/ "Multiple Part"Appendix F - Format of address mapping tables 🗺️✨
okay bestie, so we NEED a way to link up the domain namespace and the X.400 namespace from Chapter 4 🦋 when you match them up, both sides of the gateway get a way better service 💅 so defining mappings and sharing them in the format from this appendix is strongly encouraged 🫶
this syntax starts out as a table, but it's written so it can plug into domain nameservers, like the Internet Domain nameservers or the UK NRS 🧚 the mapping is not symmetric, so each direction gets its own separate table 💖 and if more than one match is possible, use the longest possible match 👑
first up, there's an address syntax that's compatible with the syntax used for 822.domains 🌸 it's meant to be used with systems that support this form of name, so it's giving compatibility 🎀
to show a null attribute, we use the pseudo-value "@" (not a printable string character) to mean "this level is omitted" 🙈 this is different from the form that includes the element with no value, though a correct X.400 implementation will interpret both in the same way ✨
and yes, this syntax is not meant for users to handle 💀
dmn-or-address = dmn-part *( "." dmn-part )
dmn-part = attribute "$" value
attribute = standard-type
/ "~" dmn-printablestring
value = dmn-printablestring
/ "@"
dmn-printablestring =
= *( dmn-char / dmn-pair )
dmn-char = <"{", "}", "*", and any ps-char
except ".">
dmn-pair = "."here's an example usage 🍓
~ROLE$Big.Chief.ADMD$ATT.C$US
PRMD$DEC.ADMD$@.C$USthe first example shows quoting a "." 💜 and the second shows the ADMD level being omitted 🦋
there are some extra restrictions on how dmn-or-address can be used 🌈
- Only C, ADMD, PRMD, O, and OU may be used.
- There must be a strict ordering of all components, with the most significant components on the RHS.
- 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, the format is this 🎀
domain-syntax "#" dmn-or-address "#"the trailing "#" is there for clarity 🙈 because dmn-or-address can produce values with trailing blanks. Lines starting with "#" are comments 💅
for example 🧚
AC.UK#PRMD$UK.AC.ADMD$GOLD 400.C$GB#
XEROX.COM#O$Xerox.ADMD$ATT.C$US#
GMD.DE#O$@.PRMD$GMD.ADMD$DBP.C$DE#and for X.400 -> domain, the format is 🌸
dmn-or-address "#" domain-syntax "#"for example 🦋
#
# Mapping table
#
PRMD$UK.AC.ADMD$GOLD 400.C$GB#AC.UK#References 📚
- [Braden89a] Braden, R., Editor, "Requirements for Internet Hosts -- Application and Support", RFC 1123, USC/Information Sciences Institute, October 1989.
- [CCITT88a] CCITT, "CCITT Recommendations X.408", Message Handling Systems: Encoded Information Type Conversion Rules, CCITT, December 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.
- [Postel82a] Postel, J., "Simple Mail Transfer Protocol", RFC 821, USC/Information Sciences Institute, August 1982.
- [Rose85a] Rose M., and E. Stefferud, "Proposed Standard for Message Encapsulation", RFC 934, January 1985.
- [Systems85a] CEN/CENELEC/Information Technology/Working Group on Private Message Handling Systems, "FUNCTIONAL STANDARD A/3222", CEN/CLC/IT/WG/PMHS N 17, October 1985.
Security Considerations 💀
Security issues are not discussed in this memo. 🙈
Author's Address 🖋️
Steve Kille University College London Gower Street WC1E 6BT England
Phone: +44-1-380-7294
EMail: S.Kille@Cs.Ucl.AC.UK 💌
📦 where this page comes from
- ietf: rfc1148 1990-03
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms