RFC 1327
Mapping between X.400(1988) / ISO 10021 and RFC 822
RFC 1327 — Mapping between X.400(1988) / ISO 10021 and RFC 822 ✨
Okay bestie, let's get into it 🎀 This one is all about making two totally different mail worlds actually talk to each other 💌
- Working group: Network Working Group
- Author: S. Hardcastle-Kille, University College London 🧑💻
- Date: May 1992 📅
- Status: IAB standards track protocol 🏆
- Obsoletes: RFCs 987, 1026, 1138, 1148 (so it replaces all four of those older docs 🫶)
- Updates: RFC 822 (so it changes the RFC 822 rules a bit 🔧)
Status of this Memo 📜
Okay so this RFC is an IAB standards track protocol for the Internet community, and it's basically asking everyone to talk about it and suggest improvements 🗣️ Want the current standardization state and status of this protocol? Check the current edition of the "IAB Official Protocol Standards" 💅 Also, distribution of this memo is unlimited, so share away 🦋
Abstract 🧚
This doc is serving mappings that let systems running the CCITT X.400 (1988) Recommendations on Message Handling Systems, also known as 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, whilst not requiring unduly complex mappings. And the mappings should not require any changes to end systems, which is so important 🙌 This document is a revision based on RFCs 987, 1026, 1138, and 1148 [Kille86a,Kille87a], which it obsoletes.
This document specifies a mapping between two protocols. This specification should be used when this mapping is performed on the DARPA Internet or in the UK Academic Community. It may be modified in the light of implementation experience, but no substantial changes are expected 🌸
Table of Contents 📋
1 - Overview ...................................... 3
1.1 - X.400 ......................................... 3
1.2 - RFC 822 ....................................... 3
1.3 - The need for conversion ....................... 4
1.4 - General approach .............................. 4
1.5 - Gatewaying Model .............................. 5
1.6 - X.400 (1984) .................................. 8
1.7 - Compatibility with previous versions .......... 8
1.8 - Aspects not covered ........................... 8
1.9 - Subsetting .................................... 9
1.10 - Document Structure ............................ 9
1.11 - Acknowledgements .............................. 9
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 ................................. 26
3.3 - Standard Types ................................ 26
3.4 - Encoding ASCII in Printable String ............ 28
4 - Addressing .................................... 30
4.1 - A textual representation of MTS.ORAddress ..... 30
4.2 - Basic Representation .......................... 31
4.3 - EBNF.822-address <-> MTS.ORAddress ............ 36
4.4 - Repeated Mappings ............................. 48
4.5 - Directory Names ............................... 50
4.6 - MTS Mappings .................................. 50
4.7 - IPMS Mappings ................................. 55
5 - Detailed Mappings ............................. 59
5.1 - RFC 822 -> X.400 .............................. 59
5.2 - Return of Contents ............................ 67
5.3 - X.400 -> RFC 822 .............................. 67
Appendix A - Mappings Specific to SMTP ..................... 91
Appendix B - Mappings specific to the JNT Mail ............. 91
1 - Introduction .................................. 91
2 - Domain Ordering ............................... 91
3 - Addressing .................................... 91
4 - Acknowledge-To: .............................. 91
5 - Trace ......................................... 92
6 - Timezone specification ........................ 92
7 - Lack of 822-MTS originator specification ...... 92
Appendix C - Mappings specific to UUCP Mail ................ 93
Appendix D - Object Identifier Assignment .................. 94
Appendix E - BNF Summary ................................... 94
Appendix F - Format of address mapping tables .............. 101
1 - Global Mapping Information .................... 101
2 - Syntax Definitions ............................ 102
3 - Table Lookups ................................. 103
4 - Domain -> O/R Address format .................. 104
5 - O/R Address -> Domain format .................. 104
6 - Domain -> O/R Address of Gateway table ........ 104
Appendix G - Mapping with X.400(1984) ...................... 105
Appendix H - RFC 822 Extensions for X.400 access ........... 106
Appendix I - Conformance ................................... 106
Appendix J - Change History: RFC 987, 1026, 1138, 1148 ..... 107
1 - Introduction .................................. 108
2 - Service Elements .............................. 108
3 - Basic Mappings ................................ 108
4 - Addressing .................................... 108
5 - Detailed Mappings ............................. 109
6 - Appendices .................................... 109
Appendix K - Change History: RFC 1148 to this Document ..... 109
1 - General ....................................... 109
2 - Basic Mappings ................................ 110
3 - Addressing .................................... 110
4 - Detailed Mappings ............................. 110
5 - Appendices .................................... 110
References ................................................. 111
Security Considerations .................................... 113
Author's Address ........................................... 113Chapter 1 -- Overview 🌈
1.1. X.400 💜
Okay so this doc is about the CCITT 1988 X.400 Series Recommendations / ISO IEC 10021 on the Message Oriented Text Interchange Service (MOTIS) 📨 The document calls this ISO/CCITT standard "X.400" for short, which is a super convenient shorthand. If it ever means the 1984 CCITT Recommendations, it'll say so explicitly 👀 X.400 defines an Interpersonal Messaging System (IPMS), and it uses a store and forward Message Transfer System. This document is only about the IPMS, not the wider application of X.400 🙈 And it's expected that X.400 will be implemented very widely, so this matters a lot 🔥
1.2. RFC 822 🌸
RFC 822 started out as a messaging standard on the DARPA (the US Defense Advanced Research Projects Agency) Internet 🇺🇸 It defines an end-to-end message format, and it gets used with a bunch of different message transfer protocol environments. Let's look at the main ones 👇
SMTP Networks 📮
On the DARPA Internet and other TCP/IP networks, RFC 822 is used alongside two other standards: RFC 821, also known as Simple Mail Transfer Protocol (SMTP) [Postel82a], and RFC 920, which is a Specification for domains and a distributed name service [Postel84a] ✨
UUCP Networks 🐚
UUCP is the UNIX to UNIX CoPy protocol. It's usually used over dialup telephone networks to give you a simple message transfer mechanism 📞 There are some extensions to RFC 822, mostly in the addressing 🧩 They use domains that conform to RFC 920, but not the corresponding domain nameservers [Horton86a] 🤓
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 the ones tied to the UK Academic Community, use the JNT (Joint Network Team) Mail Protocol, also known as Greybook [Kille84a] 🎓 That's 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 🍓
So there's a huge community using RFC 822 based protocols for mail, and they'll really want to talk to people using the IPMS from X.400 systems 🥹 This is also going to be needed when communities plan to transition over to an X.400 IPMS, because you'll need conversion to make that switch smooth ✨ It's expected that there will be more than one gateway, and this specification will help them all behave in a consistent way 🎀 Quick note: "gateway" here means a component doing the protocol mappings between RFC 822 and X.400. That's standard usage amongst mail implementors, but transport and network service implementors should read 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 underneath the details of the specification 🧠 These principles are goals, and they aren't achieved in every aspect of the specification, so don't panic if you spot a gap 🙈
- 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 🧚
- Subject to 1), 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 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 literally not relevant to gatewaying 🙈. The first two services are all about operations to originate and receive these two objects:
- IPM (Interpersonal Message) 💖: this one has two components, a heading and a body. The body is structured as a sequence of body parts, which MAY be basic components (like IA5 text or G3 fax) or IP Messages. The heading is made of fields holding end to end user information, like subject, primary recipients (
To:), and importance. - IPN (Inter Personal Notification) 🔔: 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 utilise the Message Transfer (MT) Abstract Service [CCITT/ISO88c], which gives three basic services:
- 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 mostly relate to the MTS Message (Envelope and Content), which carries an IPM or IPN (or other uninterpreted contents) 📦. There's also an Envelope, which includes an ID, an originator, and a list of recipients. Submission also includes the probe service, which supports the IPMS Probe. Delivery also includes Reports, which indicate whether a given MTS Message has been delivered or not.
The MTS is REFINED into the MTA (Message Transfer Agent) Service, which 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's an underlying service, which is called the 822-MTS service here. 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 as 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 🌉
Given this functional description of the two services, we can now think about the functional nature of a gateway. It would be elegant to map the 822-MTS service onto the MTS Service Elements and RFC 822 onto an IPM, but reality just does not fit 😭. Another elegant approach would be to treat this document as the definition of an X.400 Access Unit (AU). Again, reality does not fit 💀. It is necessary to consider that the IPM format definition, the IPMS Service Elements, the MTS Service Elements, and MTA Service Elements on one side are mapped into RFC 822 + 822-MTS on the other in a slightly tangled manner 🧶. The details of the tangle will be made clear in Chapter 5. Access to the MTA Service Elements is minimised.
The following basic mappings are thus defined. When going from RFC 822 to X.400, an RFC 822 message and the associated 822-MTS information is always mapped into an IPM (MTA, MTS, and IPMS Services). Going from X.400 to RFC 822, an RFC 822 message and the associated 822-MTS information MAY be derived from:
- 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 primary goal of this specification is to support single mappings, so that X.400 and RFC 822 users can communicate with maximum functionality ✨.
The mappings specified here are designed to work where a message traverses multiple times between X.400 and RFC 822. This is often essential, particularly in the case of distribution lists 📬. However, in general, this will lead to a level of service which is the lowest common denominator (approximately the services offered by RFC 822).
Some RFC 822 networks MAY wish to use X.400 as an interconnection mechanism (typically for policy reasons), and this is fully supported 🫶.
Where an X.400 message transfers to RFC 822 and then back to X.400, there is no expectation of X.400 services which do not have an equivalent service in standard RFC 822 being preserved, although this MAY be possible in some cases 🌈.
1.6. X.400 (1984) 🕰️
Much of this work is based on the initial specification of RFC 987 and its addendum RFC 1026, which defined a mapping between X.400(1984) and RFC 822. A basic decision is that the mapping defined in this document is to the full 1988 version of X.400, and not to a 1984 compatible subset. New features of X.400(1988) can be used to provide a much cleaner mapping than the one defined in RFC 987. This is important, to give good support to communities which will utilise full X.400 at an early date. To interwork with 1984 systems, Appendix G SHALL be followed.
If a message is being transferred to an X.400(1984) system by way of an X.400(1988) MTA, it will give a slightly better service to follow the rules of Appendix G 👑.
1.7. Compatibility with previous versions 🧩
The changes between this and older versions of the document are given in Appendices I and J. These are RFCs 987, 1026, 1138, and 1148. This document is a revision of RFC 1148 [Kille90a]. As far as possible, changes have been made in a compatible fashion 💜.
1.8. 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
- Mapping X.400 to extended versions of RFC 822, with support for multimedia content
The first two of these are really coupled. To map the X.400 services, this specification defines a number of extensions to RFC 822. As a side effect, these give the 822 user access to SOME X.400 services. However, the aim on the RFC 822 side is to preserve current service, and it is intentional that access is not given to all X.400 services. Thus, it will be a poor choice for X.400 implementors to use RFC 987(88) as an interface, because there are too many aspects of X.400 which cannot be accessed through it. If a text interface is desired, a specification targeted at X.400, without RFC 822 restrictions, would be more appropriate. Some OPTIONAL and limited extensions in this area have proved useful, and are defined in Appendix H 🧠.
1.9. Subsetting 🍰
This proposal specifies a mapping which is appropriate to preserve services in existing RFC 822 communities. Implementations and specifications which subset this specification are strongly discouraged 🙅♀️.
1.10. 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 eleven appendices 📚.
WARNING: THE REMAINDER OF THIS SPECIFICATION IS TECHNICALLY DETAILED. IT WILL NOT MAKE SENSE, EXCEPT IN THE CONTEXT OF RFC 822 AND X.400 (1988). DO NOT ATTEMPT TO READ THIS DOCUMENT UNLESS YOU ARE FAMILIAR WITH THESE SPECIFICATIONS. 🚨
1.11. Acknowledgements 🙌
The work in this specification was substantially based on RFC 987 and RFC 1148, which had input from many people, who are credited in the respective documents.
A number of comments from people on RFC 1148 led to this document. In particular, there were comments and suggestions from: Maurice Abraham (HP); Harald Alvestrand (Sintef); Peter Cowen (X-Tel); Jim Craigie (JNT); Ella Gardener (MITRE); Christian Huitema (Inria); Erik Huizer (SURFnet); Neil Jones (DEC); Ignacio Martinez (IRIS); Julian Onions (X-Tel); Simon Poole (SWITCH); Clive Roberts (Data General); Pete Vanderbilt (SUN); Alan Young (Concurrent) 💖.
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 (aka writes and sends) a message, there's a whole buffet of services on the menu 🍓. Some of them make the gateway actually do something, like delivering to a recipient, and some are just stuffing in known info, like filling out a subject line 💅. This bit tells you, for every service on offer, how well it survives the trip to a recipient who's reached through a gateway. There are three levels of support:
Supported: the protocol bits line up nicely, so the service can be fully provided ✨Not Supported: total mismatch, it just can't be provided 💀Partial Support: it can be partly fulfilled 🌸
For the first two, the service just gets labelled Supported or Not Supported (ngl, super straightforward). If there are extra implications or the (non-)support isn't obvious, we add a little explanation. For partial support, we summarise how much you actually get. If it's pretty good, we'll say something like "Supported by use of....." 🦋 A super common case is when the service gets mapped onto a non-standard thing on the other side of the gateway, which would have counted as full support if it were standard. In lots of cases that's basically the same as support 💖. For partial support we also give a hint of the mechanism, so you get a vibe for how much support you're getting. Also, this is not a replacement for Chapter 5, which has the full mapping spelled out 📖.
If a service is described as supported, that implies:
- Semantic correspondence, meaning the meanings line up 💕
- No (significant) loss of information 🫶
- Any actions required by the service element get taken care of ✅
Here's a gainer: if an RFC 822 originator sets a Subject: field, that's considered supported, because the X.400 recipient gets a subject indication 🎀.
Sometimes the required action is just making the info available to the end user. Other times, actions might mean generating a delivery report 📬.
2.1.2. Reception of Messages
For reception, the doc lists the service elements needed to pull off this mapping. Basically it's a heads-up on what a recipient might expect to see in a message that was originated remotely 👀.
2.2. RFC 822 🌈
RFC 822 doesn't really define service elements as separate from protocol elements 🤷♀️. But basically all of the RFC 822 header fields, with the exception of trace, can be seen as lining up with implicit RFC 822 service elements 💜.
2.2.1. Origination in RFC 822
So the mapping trick that gets used in a bunch of places is to stick the RFC 822 header into a heading extension in the IPM (InterPersonal Message) 🧚. This counts as partial support, since it makes the info available to any X.400 implementations that care about these services. Communities that need heavy RFC 822 interworking are recommended to require that their X.400 User Agents can display these heading extensions 🙌. Here's the header-by-header rundown:
Date:Supported. 📅From:Supported. For messages where there's also a sender field, the mapping is toAuthorising 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 toCross 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 get mapped onto text, so they're not accessible to the X.400 user as addresses. In principle, fuller support would be possible by mapping onto a forwarded IP Message, but this is not suggested. 🙈- Other Fields: in particular
X-*fields, and "illegal" fields in common usage (e.g.,Fruit-of-the-day:) are supported by use of heading extensions. 🍒
2.2.2. Reception by RFC 822
This part looks at an RFC 822 User Agent receiving a message that was originated in an X.400 system and transferred across a gateway 📨. These 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:
These non-standard services (headers) may be present too. They're 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: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 we map services from X.400 to RFC 822 that RFC 822 doesn't support, we define brand-new RFC 822 headers 🆕. The plan is to register these fields so that cooperating RFC 822 systems can 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 get provided, in part, by the gateway, since they can't be provided by RFC 822 🌸.
Some service elements are marked N/A (not applicable) 🙃. There are five cases, each marked with its own comment:
N/A (local): these elements are only applicable to User Agent / Message Transfer Agent interaction, so they can't 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 don't 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 depends 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. ForwardedIPMessage is supported, with some loss of information. Other types get some measure of support, dependent on X.400 facilities for conversion to IA5. This will only be done where content conversion is not prohibited.
- User Capabilities Registration: N/A (local).
2.3.1.2. IPM Service Optional User Facilities 🎀
This section describes support for the optional (user-selectable) IPM services listed in Section 19.9 of X.400 / ISO/IEC 10021-1, in the order given. Section 19.9 has cross references to short definitions of each service 💜.
- Additional Physical Rendition: N/A (PDAU).
- Alternate Recipient Allowed: Not supported. There is no RFC 822 service equivalent to prohibition of alternate recipient assignment (e.g., an RFC 822 system may freely send an undeliverable message to a local postmaster). Thus, the gateway cannot prevent assignment of alternative recipients on the RFC 822 side. This service really means giving the user control as to whether or not an alternate recipient is allowed. This specification requires transfer of messages to RFC 822 irrespective of this service request, and so this service is not supported. 🙅♀️
- Authorising User's Indication: Supported.
- Auto-forwarded Indication: Supported as new RFC 822 header (
Auto-Forwarded:). - Basic Physical Rendition: N/A (PDAU).
- Blind Copy Recipient Indication: Supported.
- Body Part Encryption Indication: Supported by use of a new RFC 822 header (
Original-Encoded-Information-Types:), although in most cases it will not be possible to map the body part in question. - Content Confidentiality: Not supported.
- Content Integrity: Not supported.
- Conversion Prohibition: Supported. In this case, only messages with IA5 body parts, other body parts which contain only IA5, and Forwarded IP Messages (subject recursively to the same restrictions), will be mapped.
- Conversion Prohibition in Case of Loss of Information: Supported.
- Counter Collection: N/A (PDAU).
- Counter Collection with Advice: N/A (PDAU).
- Cross Referencing Indication: Supported. 🔁
- Deferred Delivery: N/A (prior). This service should always be provided by the MTS prior to the gateway. A new RFC 822 header (
Deferred-Delivery:) is provided to transfer information on this service to the recipient. ⏰ - Deferred Delivery Cancellation: N/A (local).
- Delivery Notification: Supported. This is performed at the gateway. Thus, a notification is sent by the gateway to the originator. If the 822-MTS protocol is JNT Mail, a notification may also be sent by the recipient UA. 📬
- Delivery via Bureaufax Service: N/A (PDAU) 📠
- Designation of Recipient by Directory Name: N/A (local) 🗂️
- Disclosure of Other Recipients: Supported by use of a new RFC 822 header (
X400-Recipients:). This is just descriptive info for the RFC 822 recipient, and it is not reverse mappable 🕵️♀️ - DL Expansion History Indication: Supported by use of a new RFC 822 header (
DL-Expansion-History:). 📜 - DL Expansion Prohibited: Okay, bestie, "Distribution List" here means an MTS supported distribution list, the way X.400 does it. RFC 822 doesn't have anything like that, so RFC 822 distribution lists should be treated as an informal redistribution mechanism, outside the scope of this control. Messages still go out to RFC 822 whether or not this service is requested. So in theory this counts as supported, even though in practice it may look like it isn't 🫠
- Express Mail Service: N/A (PDAU) 🏃♀️
- Expiry Date Indication: Supported as a new RFC 822 header (
Expiry-Date:). In general, no automatic action can be expected 🙈 - Explicit Conversion: N/A (prior) 🔄
- Forwarded IP Message Indication: Supported, with some loss of information. The message gets forwarded in an RFC 822 body, so it can only be interpreted 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. A new RFC 822 header (
Latest-Delivery-Time:) is provided, which may be used by the recipient ⏰ - Message Flow Confidentiality: Not supported. 🔒
- Message Origin Authentication: N/A (reception)
- Message Security Labelling: Not supported. 🏷️
- Message Sequence Integrity: Not supported. 🧵
- Multi-Destination Delivery: Supported. 📬📬
- Multi-part Body: Supported, with some loss of information, because the structuring cannot be formalised in RFC 822 🧱
- Non Receipt Notification Request: Not supported.
- Non Repudiation of Delivery: Not supported.
- Non Repudiation of Origin: N/A (reception)
- Non Repudiation of Submission: N/A (local)
- Obsoleting Indication: Supported as 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 by use of a comment in a new RFC 822 header (
X400-Recipients:), associated with the recipient in question ✅ - Physical Forwarding Prohibited: Supported by use of a comment in a new RFC 822 header (
X400-Recipients:), associated with the recipient in question 🚫 - Prevention of Non-delivery notification: Supported, since delivery notifications can't be generated by RFC 822. In practice, errors come back as IP Messages, so this service may appear not to be supported (see Non-delivery Notification). 🙃
- Primary and Copy Recipients Indication: Supported 👑
- Probe: Supported at the gateway (i.e., the gateway services the probe). 🧚
- Probe Origin Authentication: N/A (reception)
- Proof of Delivery: Not supported.
- Proof of Submission: N/A (local)
- Receipt Notification Request Indication: Not supported.
- Redirection Allowed by Originator: Redirection means MTS supported redirection, the way X.400 does it. This doesn't exist in the RFC 822 world. RFC 822 redirection (e.g., aliasing) should be regarded as an informal redirection mechanism, beyond the scope of this control. Messages will be sent to RFC 822, irrespective of whether this service is requested. Theoretically therefore, this service is supported, although in practice it may appear that it is not supported 🔀
- Registered Mail: N/A (PDAU)
- Registered Mail to Addressee in Person: N/A (PDAU)
- Reply Request Indication: Supported as 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 services required must be dealt with at submission time. Any such request is made available through the gateway by use of a comment associated with the recipient in question 📝
- Return of Content: In principle this is N/A, since non-delivery notifications are not supported. In practice, most RFC 822 systems will return part or all of the content along with the IP Message indicating an error (see Non-delivery Notification). 📦
- Sensitivity Indication: Supported as 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). Theoretically, this service is N/A (prior). In practice, because of informal RFC 822 lists, it can be regarded as supported 🫶
2.3.2. Reception by X.400
2.3.2.1. Standard Mandatory Services
Bestie, these standard IPM mandatory user facilities are 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
Same energy here: these standard IPM optional user facilities are 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
Okay, so 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 be present in RFC 822 originated messages that get received by an X.400 UA. Iconic 💜
Chapter 3 Basic Mappings 🎀
3.1. Notation
The X.400 protocols are encoded in a structured way according to ASN.1, whereas RFC 822 is text encoded 📝. So to define a detailed mapping, you have to refer to detailed protocol elements in each format. This section describes the notation that does that 🦋
3.1.1. RFC 822
Structured text is defined according to the Extended Backus Naur Form (EBNF) defined in Section 2 of RFC 822 [Crocker82a]. In the EBNF definitions used in this specification, the syntax rules given in Appendix D of RFC 822 are assumed. When these EBNF tokens are referred to outside an EBNF definition, they are identified by the string "822." appended to the beginning of the string (e.g., 822.addr-spec). Additional syntax rules, to be used throughout this specification, are defined in this chapter 🧠
The EBNF is used in two ways, bestie:
- 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 shall 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.importance). - To describe the structure of IA5 or ASCII information 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, except for the following cases, where LWSP may be inserted according to RFC 822 rules.
- Around the ":" in all headers
EBNF.labelled-integerEBNF.object-identifierEBNF.encoded-info
RFC 822 folding rules are applied to all headers 🫧
3.1.2. ASN.1
An element is referred to with the following syntax, defined in EBNF 💅:
element = service "." definition *( "." definition )
service = "IPMS" / "MTS" / "MTA"
definition = identifier / context
identifier = ALPHA *< ALPHA or DIGIT or "-" >
context = "[" 1*DIGIT "]"The EBNF.service keys are shorthand for the following service specifications:
IPMS:IPMSInformationObjectsdefined in Annex E of X.420 / ISO 10021-7.MTS:MTSAbstractServicedefined in Section 9 of X.411 / ISO 10021-4.MTA:MTAAbstractServicedefined in Section 13 of X.411 / ISO 10021-4.
The first EBNF.identifier identifies a type or value key in the context of the defined service specification. Subsequent EBNF.identifiers identify a value label or type in the context of the first identifier (SET or SEQUENCE). EBNF.context indicates a context tag, and is used where there is no label or type to uniquely identify a component. The special EBNF.identifier keyword "value" is used to denote an element of a sequence 🌈
For example, IPMS.Heading.subject defines the subject element of the IPMS heading. The same syntax is also used to refer to element values. For example:
MTS.EncodedInformationTypes.[0].g3Fax refers to a value of MTS.EncodedInformationTypes.[0] .3.2. ASCII and IA5
A gateway will interpret all IA5 as ASCII. So the mapping between these forms is only conceptual 🌙
3.3. Standard Types
There is a need to convert between ASCII text and some of the types defined in ASN.1 [CCITT/ISO88d] 🔁. For each case, an EBNF syntax definition is given, for use in all of this specification, which leads to a mapping between ASN.1 and an EBNF construct. All EBNF syntax definitions of ASN.1 types are in lower case, whereas ASN.1 types are referred to with the first letter in upper case. Except as noted, all mappings are symmetrical 🪞
3.3.1. Boolean
Boolean is encoded as:
boolean = "TRUE" / "FALSE"3.3.2. NumericString
NumericString is encoded as:
numericstring = *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 💌
okay so, when T.61 strings are only there to carry stuff a human is going to read, the whole point is making the characters look right on the other end ✨. It's not about keeping every bit perfectly reversible. For those cases, the mappings to IA5 from CCITT Recommendation X.408 (1988) SHALL be used [CCITT/ISO88a]. After that, they get encoded in ASCII 🫶.
There's also a need to show Teletex Strings in ASCII for some bits of O/R Address 🎀. The encoding looks like this:
teletex-string = *( ps-char / t61-encoded )
t61-encoded = "{" 1* t61-encoded-char "}"
t61-encoded-char = 3DIGITCommon characters just get mapped straight across 🍓. Everything else goes through a quoting trick that's kinda like the printable string one 🙈. Each octet is written as 3 decimal digits.
A bunch of places can have a Teletex and/or Printable String version of the same string 💖, so here's the BNF for that:
teletex-and-or-ps = [ printablestring ] [ "*" teletex-string ]The natural mapping is restricted to EBNF.ps-char, which keeps the full BNF easier to parse 🧠.
3.3.5. UTCTime ⏰
Both UTCTime and the RFC 822 822.date-time syntax have: 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 honestly that's redundant 🙄. So a symmetrical mapping can be made between these two constructs ✨.
Note: In practice, a gateway will need to parse various illegal variants of822.date-time😬. When822.date-timecan't be parsed, it is RECOMMENDED that the derived UTCTime is set to the value at the time of translation.
When mapping to X.400, the UTCTime format which specifies the timezone offset SHALL be used 💅.
When mapping to RFC 822, the 822.date-time format SHALL include a numeric timezone offset (e.g., +0000) 🌍.
When mapping time values, the timezone SHALL be preserved as specified. The date SHALL NOT be normalised to any other timezone 🙅♀️. no sneaky timezone shifting, bestie 💜
3.3.6. Integer 🔢
A basic ASN.1 Integer will be mapped onto EBNF.numericstring. In lots of cases ASN.1 enumerates Integer values or uses ENUMERATED, so there's an EBNF encoding called labelled-integer for that 👑. When going from EBNF to ASN.1, only the integer value gets mapped and the text is thrown away. When going 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, 0-9, and "-">3.3.7. Object Identifier 🆔
Object identifiers are written in a style similar to ASN.1's, and the order is the same as ASN.1's (big-endian) ✨. The numbers are mandatory and get used when mapping from ASCII to ASN.1 🔑. The key-strings are optional 🌸. It is RECOMMENDED that as many strings as possible get generated when mapping from ASN.1 to ASCII, so that users can actually recognise them 🥰.
object-identifier ::= oid-comp object-identifier
| oid-comp
oid-comp ::= [ key-string ] "(" numericstring ")"An example representation of an object identifier looks like this:
joint-iso-ccitt(2) mhs (6) ipms (1) ep (11) ia5-text (0)
or
(2) (6) (1)(11)(0)3.4. Encoding ASCII in Printable String 🖨️
Some info in RFC 822 is represented in ASCII, and it needs to be mapped into X.400 elements encoded as printable string 📨. So we need a way to represent ASCII encoded as PrintableString 🎀.
A structured subset of EBNF.printablestring is now defined. This SHALL 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 read in decimal as the matching ASCII character 🔢. Special encodings are given for the at sign @, percent %, exclamation mark / bang !, double quote ", underscore _, left bracket (, and right bracket ) 🪄. These characters, apart from the round brackets, are not included in PrintableString, but they're super common in RFC 822 addresses 📬. The abbreviations make it way easier to write RFC 822 addresses from an X.400 system. These special encodings SHALL be interpreted in a case insensitive manner, but always generated in lower case 🔡.
A reversible mapping between PrintableString and ASCII can now be defined 🔁. The reversibility means that some printable string values (the ones with round braces) can't be generated from ASCII. So this mapping MUST only be used in cases where the printable strings can only be derived from ASCII, which means the domain is restricted 🚧. For example, here it only gets applied to a Domain Defined Attribute that this specification generated, so a value like "(" would never be possible 🙈.
To encode ASCII as PrintableString, use the EBNF.ps-encoded syntax, with all EBNF.ps-restricted-char mapped directly. All other 822.CHAR values get encoded as EBNF.ps-encoded-char ✨.
To encode PrintableString as ASCII, parse it as EBNF.ps-encoded, then reverse the previous mapping. If the PrintableString can't be parsed, then the mapping is being applied to an inappropriate value, and an error SHALL be given to the procedure doing the mapping 🚨. In some cases, it MAY be preferable to pass the printable string through unaltered 🤷♀️.
Some examples now follow. Notice the arrows, which show the 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) <-> (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 🧩.
We start with 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 are each treated as defined by a construct like this one. In an RFC 822 header, EBNF.822-address is wrapped in the 822.address syntax rule, and there may also be comments attached 💬. None of that extra info has any semantics, except to the end user 🙃.
The basic X.400 O/R Address, which the MTS uses for routing, is defined by MTS.ORAddress 🛣️. In IPMS, MTS.ORAddress is wrapped inside IPMS.ORDescriptor 🎁.
So 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 🧩. Being able to encode this in ASCII is clearly necessary for gatewaying 🌉. All components SHALL be encoded, so that error messages are guaranteed to come back and third party replies can be optimised 💌.
4.2. Basic Representation 💎
An O/R Address has a number of structured and unstructured attributes 🧱. For each unstructured attribute, a key and an encoding are specified. For structured attributes, the X.400 attribute is mapped onto one or more attribute value pairs. For domain defined attributes, each element of the sequence maps onto a triple (a key and two values), with each value having the same encoding 🔑. The attributes are listed below, with the 1984 attributes in the first part of the table. For each attribute there's a reference, which points 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 P 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-SERVICE P 18.3.11 7
MTS.PhysicalDeliveryCountryName PD-C P 18.3.13 8
MTS.PostalCode PD-CODE 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-ADDRESS P/T 18.3.4 12
MTS.PhysicalDeliveryPersonName PD-PN P/T 18.3.17 13
MTS.PhysicalDeliveryOrganizationName PD-O P/T 18.3.16 14
MTS.ExtensionPhysicalDelivery
AddressComponents PD-EXT-DELIVERY P/T 18.3.5 15
MTS.UnformattedPostalAddress PD-ADDRESS P/T 18.3.25 16
MTS.StreetAddress PD-STREET P/T 18.3.22 17
MTS.PostOfficeBoxAddress PD-BOX P/T 18.3.18 18
MTS.PosteRestanteAddress PD-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 21Okay so the table keeps going, and these last rows are the extended network address and terminal type entries 🎀
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 T-TY I 18.3.24 23Okay so the keys point at different EBNF encodings, and they're all tied to 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-addressBestie, the BNF for presentation-address is taken straight from "A String Encoding of Presentation Address" [Kille89a] 📚
Most of the time the EBNF encoding maps straight onto the ASN.1 encoding of the attribute, no cap 🫶 There are a few exceptions though 👀 When an attribute can be either a PrintableString or a NumericString (Country, ADMD, PRMD), either form gets mapped into the BNF. And when generating ASN.1, the NumericString encoding SHALL be used if the string contains only digits 🔢
The P/T (teletex-and-or-ps) representation shows up a lot 💜 When the key maps to a single attribute, that choice is reflected in the attribute's encoding (attributes 10-21). For most of the 1984 attributes and common name, there's a printablestring version and a teletex version, and this pair gets squished into the single component here. It's iconic, honestly, because it gives a clean mapping for the common cases where only one form of the name is used ✨
Recently, ISO has been working on a string form of O/R Address [CCITT/ISO91a] 🌈 It specifies a bunch of string keywords for attributes. RFC 1148 was an input to that work, so a lot of the keywords are the same. To increase compatibility, the following alternative values SHALL be recognised when mapping from RFC 822 to X.400. These SHALL NOT be generated when mapping from X.400 to RFC 822 🙈
Keyword Alternative
ADMD A
PRMD P
GQ Q
X121 X.121
UA-ID N-ID
PD-OFFICE-NUMBER PD-OFFICE NUMBERWhen mapping from RFC 822 to X.400, the keywords OU1, OU2, OU3, and OU4 SHALL be recognised. If these are present, no keyword OU SHALL be present. These get treated as ordered values of OU 🧚
4.2.1. Encoding of Personal Name 🎀
Okay, so handling Personal Name and Teletex Personal Name purely with the EBNF.standard-type syntax from above is gonna be clumsy 😭 It makes way more sense to use the "human" conventions for encoding these parts. So a syntax is defined that 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. - Surname does not contain full stop in the first two characters.
- If Surname is the only component, it does not contain full stop.
Here's the EBNF:
encoded-pn = [ given "." ] *( initial "." ) surname
given = 2*<ps-char not including ".">
initial = ALPHA
surname = printablestringThis is used to map from any string containing only printable string characters to an O/R address personal name. To go from a string to O/R Address components, you parse the string according to the EBNF. The given name and surname get assigned directly, and all EBNF.initial tokens are concatenated without intervening full stops to make the initials component 💅
For an O/R address that follows the restrictions above, a string is derived in the natural manner, 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 defined encoding is "natural" when either GivenName or Initials is present, but not both. Encoding the case where both are present is possible, but it appears to be contrived 🙈
4.2.2. Standard Encoding of MTS.ORAddress 🦋
Given this structure, we can specify a BNF representation of an O/R Address:
std-or-address = 1*( "/" attribute "=" value ) "/"
attribute = standard-type
/ "RFC-822"
/ registered-dd-type
/ dd-key "." std-printablestring
standard-type = key-string
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 = "$" ps-charThe standard-type is any key defined in the table in Section 4.2, except PN and DD. The BNF leads to a set of attribute/value pairs, and the value gets interpreted according to the EBNF encoding defined in the table 💜
If the standard-type is PN, the value is interpreted according to EBNF.encoded-pn, and the components of MTS.PersonalName and/or MTS.TeletexPersonalName get derived accordingly.
If dd-key is the recognised Domain Defined string (DD), then the type and value are interpreted according to the syntax implied by the encoding, and aligned to either the teletex or printable string form. Key and value SHALL have the same encoding 🫶
If value is "RFC-822", then the (printable string) Domain Defined Type of "RFC-822" is assumed. This is an optimised encoding of the domain defined type defined by this specification ⭐
The matching of all keywords SHALL be done in a case-independent manner 🌸
EBNF.std-or-address uses the characters "/" and "=" as delimiters. But Domain Defined Attributes and any value may contain these characters, so a quoting mechanism using the non-printable string "$" lets you represent them 🧚
If the value is registered-dd-type, and the value is registered at the Internet Assigned Numbers Authority (IANA) as an accepted Domain Defined Attribute type, then the value SHALL 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 entirely 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 in order to work.
So an asymmetrical mapping is defined, which can be symmetrical wherever there's appropriate administrative control 💖
4.3.1. X.400 encoded in RFC 822 ✨
Okay bestie, so the std-or-address syntax is how we squish O/R Address info into the 822.local-part of an EBNF.822-address 💅. Sometimes there's extra O/R Address info hanging out in the 822.domain too, but that can't be used in the general case 😭. Why? Character set problems, plus there are different variants of X.400 O/R Addresses that use different attribute types. The only way to fit the full PrintableString character set into a domain is the 822.domain-ref syntax (aka 822.atom), and that is likely to cause problems on many systems 💀. Real talk, the characters you can actually use in domains are already way smaller than the RFC 822 set, thanks to domain conventions, policy, and restrictions in RFC 821 🙈.
A generic 822.address is a 822.local-part plus a sequence of 822.domains, like <@domain1,@domain2:user@domain3> 🦋. Every domain except the one attached to the 822.local-part (that's domain3 in this case) is just routing within the RFC 822 world, so the gateway won't interpret it. (They might have helped the gateway get identified from inside RFC 822 land, though 🧚.)
The 822.domain tied to the 822.local-part is the one that identifies the gateway from within the RFC 822 world 👑. This final domain can also be used to figure out some O/R Address attributes, as long as that doesn't clash with its first job. RFC 822 routing to gateways is usually set up so the domain does both jobs at once, which is so iconic 🌈. The O/R Address attributes are treated as a hierarchy, and a domain can specify them in this order:
Country, ADMD, PRMD, Organisation, Organisational UnitThere can be multiple Organisational Units 🌸.
There's a global mapping between domain specs and sets of attributes, and it works hierarchically ✨. If a domain implies an ADMD, it also implies a country. Subdomains underneath that get associated according to the O/R Address hierarchy. For example:
=> "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 someone would keep a domain/attribute mapping instead of just using plain subdomains 🎀:
- It's a shorthand that avoids repeating X.400 info. Like, there's often only one ADMD per country, so it doesn't need to be spelled out every time 💖.
- It handles cases where attribute values don't fit the syntax. The restricted syntax looks like this:
domain-syntax = alphanum [ *alphanumhyphen alphanum ]
alphanum = <ALPHA or DIGIT>
alphanumhyphen = <ALPHA or DIGIT or HYPHEN>Yes, RFC 822 allows a more general syntax, but this restricted one was picked because it's the one the various domain service administrations already use 🧁.
- It deals with missing elements in the hierarchy 🫶. A domain can be associated with an omitted attribute alongside several present ones. When you're algorithmically inserting lower components, the omitted value shall 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". Attributes can also have null values, and those get treated separately from omitted attributes. It would be bad practice to treat the two cases differently, but they still must be allowed for 😭.
This set of mappings needs to be known by the gateways that relay between the RFC 822 world and the O/R Address space tied to the mapping in question. There needs to be a single global definition of this set of mappings 🚨. A mapping implies an administrative equivalence between the two mapped parts of the namespaces. To route correctly in all cases, every gateway has to know the mapping. To help distribute a global set of mappings, a format for exchanging this info is defined in Appendix F 📮.
Now the remaining attributes get encoded on the LHS, using the EBNF.std-or-address syntax. Check out this example 👀:
/I=J/S=Linnimouth/GQ=5/@Marketing.Widget.COMThat encodes 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 get encoded on the LHS. In an extreme case, all of the attributes end up on the LHS 🌀. Since the domain can't be null, the RHS is just going to be a domain that indicates the gateway ✨.
The RHS (domain) encoding is designed to handle common addresses cleanly, so the amount of info on the RHS is 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 need an LHS encoding 🦋.
There's another mechanism that simplifies the encoding of common cases 🧚. It applies when the only attributes going on the LHS are (non-Teletex) Personal Name attributes that comply with the restrictions of 4.2.1. To make it work, the 822.local-part shall be encoded as EBNF.encoded-pn. Using the previous example, if the GenerationQualifier wasn't present, it would map with the RFC 822 address J.Linnimouth@Marketing.Widget.COM 🥰.
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. Most of the time, this gets done by registering the higher levels and assuming the gateway can handle the lower levels 🫧.
4.3.2. RFC 822 encoded in X.400 🌷
Sometimes the encoding from above can be reversed, which gives a "natural" encoding of genuine RFC 822 addresses 🦄. Whether that works depends a lot on how the management domains are allocated 🧸.
The general case is mapped using domain defined attributes 💖. There's a domain defined type called "RFC-822". Its attribute value is an ASCII string encoded according to Section 3.3.3 of this specification. What the ASCII string means depends on the context of the gateway 🤔:
- In the context of RFC 822, and RFC 920 [Crocker82a,Postel84a], the string can be used directly 💅.
- In the context of the JNT Mail protocol, and the NRS [Kille84a,Larmouth83a], the string shall be interpreted according to Mailgroup Note 15 [Kille84b] 📬.
- In the context of UUCP based systems, the string shall be interpreted as defined in [Horton86a] 🐚.
Other O/R Address attributes are used to identify the context the O/R Address will be interpreted in 🔍. That 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 "@" is PrintableString encoded as "(a)" 🙈. In the second example, the "RFC-822" domain defined attribute is interpreted everywhere within the (Private) Management Domain. In the first example, further attributes are needed within the Management Domain to identify a gateway. So this scheme works with varying levels of Management Domain co-operation 🌈.
There's a limit of 128 characters for the value of a domain defined attribute, and an O/R Address can have a maximum of four domain defined attributes 📏. When the printable string generated from the RFC 822 address exceeds that, additional domain defined attributes get used so up to 512 characters can be encoded ✨. These attributes shall be filled completely before the next one is started. The DDA keywords are: RFC822C1; RFC822C2; RFC822C3. Longer addresses cannot be encoded 😭.
Just like in 4.3.1, there's a way to associate parts of the O/R Address hierarchy with domains 🦋. It's an analogous global mapping, and in most cases it's going to be the inverse of the domain to O/R address mapping. It's maintained separately because there can be differences. For example, two alternate domain names might map to the same set of O/R address components 🫶.
4.3.3. Component Ordering 🎀
In most cases, the ordering of O/R Address components doesn't matter for the mappings specified here 💅. However, Organisational Units (printable string and teletex forms) and Domain Defined Attributes are specified as SEQUENCE in MTS.ORAddress, so their order might matter 👀. This spec needs to account for that in two ways:
- It keeps mapping into the domain hierarchy consistent 🏗️.
- It preserves order over multiple mappings 🔁.
There are three places where an order is 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 the components that can 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 exist for the following reasons:
- Alignment to the hierarchy of other components in RFC 822 addresses, so Organisational Units appear in the same order whether they're encoded on the RHS or LHS. Note the differences of JNT Mail as described in Appendix B 🧩.
- Backwards compatibility with RFC 987/1026 ⏪.
- To make sure gateways generate consistent addresses. This helps end users, and it generates identical message ids 🪪.
Further, it is recommended that all other attributes are generated according to this ordering, so that all attributes encoded that way follow a consistent hierarchy 🌟. When generating 822.msg-id, this order shall be followed.
- 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 that's a Management Domain issue 🙃.
4.3.4. RFC 822 -> X.400 ✨
okay so there are two basic cases here, bestie 🫶
- X.400 addresses encoded in RFC 822. This also includes RFC 822 addresses that get reversible encodings 🦋
- "Genuine" RFC 822 addresses, aka the real deal 💅
The mapping SHALL proceed as follows, and we start by assuming case 1) 🎀
STAGE I. ⭐
- If the 822-address is not of the form:
local-part "@" domainthen take the domain which will be routed on and apply step 2 of stage 1 to derive (a possibly null) set of attributes. Then go to stage II.
NOTE: It may be appropriate to reduce a source route address to this form by removal of all bar the last domain. In terms of the design intentions of RFC 822, this would be an incorrect action. However, in most real cases, it will do the "right" thing and provide a better service to the end user. This is a reflection on the excessive and inappropriate use of source routing in RFC 822 based systems. Either approach, or the intermediate approach of stripping only domain references which reference the local gateway are conformant to this specification.
- Attempt to parse
EBNF.domainas:
*( domain-syntax "." ) known-domainWhere EBNF.known-domain is the longest possible match in the set of globally defined mappings (see Appendix F). If this fails, and the EBNF.domain does not explicitly identify the local gateway, go to stage II. If the domain explicitly identifies the gateway, allocate no attributes. Otherwise, allocate the attributes associated with EBNF.known-domain. For each component, systematically allocate the attribute implied by each EBNF.domain-syntax component in the order: C, ADMD, PRMD, O, OU. Note that if the mapping used identifies an "omitted attribute", then this attribute SHOULD be omitted in the systematic allocation. If this new component exceeds an upper bound (ADMD: 16; PRMD: 16; O: 64; OU: 32) or it would lead to more than four OUs, then go to stage II with the attributes derived.
At this stage, a set of attributes has been derived, which will give appropriate routing within X.400. If any of the later steps of Stage I force use of Stage II, then these attributes SHOULD be used in Stage II. 💖
- If the
822.local-partuses the822.quoted-stringencoding, remove this quoting. If this unquoted822.local-parthas leading space, trailing space, or two adjacent spaces, go to stage II. - If the unquoted
822.local-partcontains any characters not inPrintableString, go to stage II. - Parse the (unquoted)
822.local-partaccording to the EBNFEBNF.std-or-address. Checking of upper bounds SHOULD NOT be done at this point. If this parse fails, parse the local-part according to the EBNFEBNF.encoded-pn. If this parse fails, go to stage II. The result is a set of type/value pairs. If the set of attributes leads to an address of any form other than mnemonic form, then only these attributes SHOULD be taken. If (for mnemonic form) the values generated conflict with those derived in step 2 (e.g., a duplicated country attribute), the domain is assumed to be a remote gateway. In this case, take only the LHS derived attributes, together with any RHS derived attributes which are more significant than the most significant attribute which is duplicated (e.g., if there is a duplicate PRMD, but no LHS derived ADMD and country, then the ADMD and country SHOULD be taken from the RHS). Otherwise, add LHS and RHS derived attributes together. 🔥 - Associate the
EBNF.attribute-valuesyntax (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.ORAddressspecification and to the restrictions on this set given in X.400, and that no upper bounds are exceeded for any attribute. 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. This implies that the address must refer to a recipient on an RFC 822 system. Such addresses SHALL be encoded in an X.400 O/R Address using a domain defined attribute. 🦋
- Convert the
EBNF.822-addresstoPrintableString, as specified in Chapter 3. - Generate the "RFC-822" domain defined attribute from this string.
- Build the rest of the O/R Address in the manner described below.
It may not be possible to encode the domain defined attribute due to length restrictions. If the limit is exceeded by a mapping at the MTS level, then the gateway SHALL reject the message in question. If this occurs at the IPMS level, then the action will depend on the policy being taken for IPMS encoding, which is discussed in Section 5.1.3. 😭
If Stage I has identified a set of attributes, use these to build the remainder of the address. The administrative equivalence of the mappings will ensure correct routing through X.400 to a gateway back to RFC 822. 🧚
If Stage I has not identified a set of attributes, the remainder of the O/R address effectively identifies a source route to a gateway from the X.400 side. There are three cases, and they're each handled differently:
822-MTS Return Address
This SHALL be set up so that errors are returned through the same gateway. Therefore, the O/R Address of the local gateway SHALL be used. 💌
IPMS Addresses
These are optimised for replying. In general, the message may end up anywhere within the X.400 world, and so this optimisation identifies a gateway appropriate for the RFC 822 address being converted. The 822.domain to which the address would be routed is used to select an appropriate gateway. A globally defined set of mappings is used, which identifies (the O/R Address components of) appropriate gateways for parts of the domain namespace. The longest possible match on the 822.domain defines which gateway to use. The table format for distribution of this information is defined in Appendix F.
This global mapping is used for parts of the RFC 822 namespace which do not have an administrative equivalence with any part of the X.400 namespace, but for which it is desirable to identify a preferred X.400 gateway in order to optimise routing.
If no mapping is found for the 822.domain, a default value (typically that of the local gateway) is used. It is never appropriate to ignore the globally defined mappings. In some cases, it may be appropriate to locally override the globally defined mappings (e.g., to identify a gateway close to a recipient of the message). This is likely to be where the global mapping identifies a public gateway, and the local gateway has an agreement with a private gateway which it prefers to use. 🌸
822-MTS Recipient
As the RFC 822 and X.400 worlds are fully connected, there is no technical reason for this situation to occur. In some cases, routing may be configured to connect two parts of the RFC 822 world using X.400. The information that this part of the domain space should be routed by X.400 rather than remaining within the RFC 822 world will be configured privately into the gateway in question. The O/R address SHALL then be generated in the same manner as for an IPMS address, using the globally defined mappings. It is to support this case that the definition of the global domain to gateway mapping is important, as the use of this mapping will lead to a remote X.400 address, which can be routed by X.400 routing procedures. The information in this mapping SHALL NOT be used as a basis for deciding to convert a message from RFC 822 to X.400. 🚫
4.3.4.1. Heuristics for mapping RFC 822 to X.400 🍓
RFC 822 users will often use an LHS encoded address to identify an X.400 recipient. Because the syntax is fairly complex, a number of heuristics may be applied to facilitate this form of usage. A gateway SHOULD take care not to be overly "clever" with heuristics, as this may cause more confusion than a more mechanical approach. The heuristics are as follows:
- Ignore the omission of a trailing "/" in the std-or syntax.
- If there is no ADMD component, and both country and PRMD are present, the value of
/ADMD= /(single space) is assumed. - Parse the unquoted local part according to the EBNF
colon-or-address. This may facilitate users used to this delimiter.
colon-or-address = 1*(attribute "=" value ";" *(LWSP-char))The remaining heuristic relates to ordering of address components. 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. 🙈
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 a MTS Recipient O/R Address is interpreted, gatewaying will be selected if there is a single "RFC-822" domain defined attribute present and the local gateway is identified by the remainder of the O/R Address. 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. Use of this approach is conformant to this specification. 💅
Mapping A 🎀
- Map the domain defined attribute value to ASCII, as defined in Chapter 3.
Mapping B ✨
okay so Mapping B is for X.400 addresses that DON'T use the explicit RFC 822 encoding 🎀 here's how it goes:
- Clean up the strings 🧹 For all string encoded attributes:
- remove any leading or trailing spaces, and replace adjacent spaces with a single space.
- The only attribute which is permitted to have zero length is the ADMD. This should be mapped onto a single space.
- These transformations are for lookup only. If an
EBNF.std-or-addressmapping is used as in 4), then the original values should be used.
- Country codes 🌍 Map numeric country codes to the two letter values.
- Find the domain 🔎 Noting the hierarchy specified in 4.3.1 and including omitted attributes, determine the maximum set of attributes which have an associated domain specification in the globally defined mapping. If no match is found, allocate the domain as the domain specification of the local gateway, and go to step 5.
Note: It might be appropriate to use a non-local domain. This would be selected by a global mapping analogous to the one described at the end of 4.3.4. This is not done, primarily because use of RFC 822 to connect X.400 systems is not expected to be significant.
In cases where the address refers to an X.400 UA, it is important that the generated domain will correctly route to a gateway. In general, this is achieved by carefully co-ordinating RFC 822 routing with the definition of the global mappings, as there is no easy way for the gateway to make this check. One rule that shall be used is that domains with only one component will not route to a gateway. If the generated domain does not route correctly, the address is treated as if no match is found.
- Build the subdomains 🧩 The mapping identified in 3) gives a domain, and an O/R address prefix. Follow the hierarchy: C, ADMD, PRMD, O, OU. For each successive component below the O/R address prefix, which 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 shall not be mapped onto subdomain, as822.local-partcannot be null. If there are omitted attributes in the O/R address prefix, these will have been mapped correctly and uniquely to a domain component. Where there is an attribute omitted below the prefix, all attributes remaining in the O/R address shall be encoded on the LHS. This is to ensure a reversible mapping. For example, if there is an address/S=XX/O=YY/ADMD=A/C=NN/and a mapping for/ADMD=A/C=NN/is used, then/S=XX/O=YY/is encoded on the LHS. - Local part time 🎀 If the address is not mnemonic form (form 1 variant 1), then all of the attributes in the address should be encoded on the LHS in
EBNF.std-or-addresssyntax, as described below.
For addresses of mnemonic form, if the remaining components are personal-name components, conforming to the restrictions of 4.2.1, then EBNF.encoded-pn is derived to form 822.local-part. In other cases the remaining components are simply encoded as 822.local-part using the EBNF.std-or-address syntax. If necessary, the 822.quoted-string encoding is used. The following are examples of legal quoting: "a b".c@x and "a b.c"@x. Either form may be generated, but the latter is preferred.
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 🔁
okay so there are two types of repeated mapping:
- A recursive mapping, where the repeat is within one gateway
- A source route, where the repetition occurs across multiple gateways
4.4.1. Recursive Mappings 🪞
it's possible to supply an address which is recursive at a single gateway. For example:
C = "XX"
ADMD = "YY"
O = "ZZ"
"RFC-822" = "Smith(a)ZZ.YY.XX"This is mapped first to an RFC 822 address, and then back to the X.400 address:
C = "XX"
ADMD = "YY"
O = "ZZ"
Surname = "Smith"In some situations this type of recursion may be frequent. It is important that where this occurs, no unnecessary protocol conversion occurs. This will minimize loss of service. 💅
4.4.2. Source Routes 🛣️
The mappings defined are symmetrical and reversible across a single gateway. The symmetry is particularly useful in cases of (mail exploder type) distribution list expansion. For example, an X.400 user sends to a list on an RFC 822 system which he belongs to. The received message will have the originator and any 3rd party X.400 O/R Addresses in correct format (rather than doubly encoded). In cases (X.400 or RFC 822) where there is common agreement on gateway identification, then this will apply to multiple gateways.
When a message traverses multiple gateways, the mapping will always be reversible, in that a reply can be generated which will correctly reverse the path. In many cases, the mapping will also be symmetrical, which will appear clean to the end user. For example, if countries "AB" and "XY" have RFC 822 networks, but are interconnected by X.400, the following may happen. The originator specifies:
Joe.Soap@Widget.PTT.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 is 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.
Note: There is ongoing work on specification of a "user friendly" format for directory names. If this is adopted as an internet standard, it will be recommended, but not required, for use here. 🌸
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 are made for each component of MTS.PerRecipientMessageSubmissionFields:
recipient-name: This is derived from the 822-MTS recipient by the basic ORAddress mapping.originator-report-request: This is to be set according to content return policy, as discussed in Section 5.2.explicit-conversion: This optional component is omitted, as this service is not needed.extensions: The default value (no extensions) is 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 will be present in these fields. In some cases a (positive) delivery report will be generated.
4.6.2.1. 822-MTS Mappings 🧠
Use the basic ORAddress mapping, to generate the 822-MTS originator (return address) from MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName). If MTS.ORName.directory-name is present, it is discarded. (Note that it will be presented to the user, as described in 4.6.2.2.)
The 822-MTS recipient is conceptually generated from MTS.OtherMessageDeliveryFields.this-recipient-name. This is done by taking MTS.OtherMessageDeliveryFields.this-recipient-name, and generating an 822-MTS recipient according to the basic ORAddress mapping, discarding MTS.ORName.directory-name if present. However, if this model was followed exactly, there would be no possibility to have multiple 822-MTS recipients on a single message. This is unacceptable, and so layering is violated. The mapping needs to use the MTA level information, and map each value of MTA.PerRecipientMessageTransferFields.recipient-name, where the responsibility bit is set, onto an 822-MTS recipient. 🙅♀️
4.6.2.2. Generation of RFC 822 Headers 🎀
okay so not ALL the per-recipient info can make it through at the 822-MTS level 😭 which is kinda tragic, so we make two brand-new RFC 822 headers to carry it over to the RFC 822 recipient 💌. they're called X400-Originator: and X400-Recipients: ✨
the X400-Originator: field gets set to the exact same value as the 822-MTS originator 🫶. and if MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName) contains MTS.ORName.directory-name, then that Directory Name shall be represented in an 822.comment. no skipping that part, bestie 💅
recipient names get pulled from every value of MTS.OtherMessageDeliveryFields.this-recipient-name and MTS.OtherMessageDeliveryFields.other-recipient-names, and they're made available to the RFC 822 user through the X400-Recipients: field. taking the recipients at the MTS level means disclosure of recipients gets handled correctly 🙌 but ngl that clashes with wanting to optimise mail transfer 😤. there's no problem when disclosure of recipients is allowed. there's also no problem if there's only one RFC 822 recipient, since the X400-Recipients field only gets one address in that case 🦋
the drama starts when there are multiple RFC 822 recipients AND disclosure of recipients is prohibited 💀. two options are allowed:
- generate one copy of the message for each RFC 822 recipient, with the
X400-Recipientsfield set correctly to the recipient of that copy. this is functionally correct, but it's likely to be more expensive 💸 - discard the per-recipient information, and insert this field:
X400-Recipients: non-disclosure:;option 2 is the recommended option 👑
a third option of ignoring the disclosure flag is not allowed 🙅♀️. if any MTS.ORName.directory-name is present, it shall be represented in an 822.comment. period 💖
if MTS.OtherMessageDeliveryFields.orignally-intended-recipient-name is present, then there has been redirection, or there has been distribution list expansion 🦋. distribution list expansion is a per-message option, and the info for that lives in the DL-Expansion-History: field described in Section 5.3.6 📜. everything else gets represented in an 822.comment attached to MTS.OtherMessageDeliveryFields.this-recipient-name 💬. the message may be delivered to different RFC 822 recipients, so several addresses in the X400-Recipients: field may have these comments 🧚. the one WITHOUT a comment is the RFC 822 recipient ✨. the EBNF of the comment is:
redirect-comment =
[ "Originally To:" ] mailbox "Redirected"
[ "Again" ] "on" date-time
"To:" redirection-reason
redirection-reason =
"Recipient Assigned Alternate Recipient"
/ "Originator Requested Alternate Recipient"
/ "Recipient MD Assigned Alternate Recipient"it's derived from MTA.PerRecipientMessageTransferFields.extension.redirection-history 🔍. an example of this looks like:
X400-Recipients: postmaster@widget.com (Originally To:
sales-manager@sales.widget.com Redirected
on Thu, 30 May 91 14:39:40 +0100 To: Originator Assigned
Alternate Recipient postmaster@sales.widget.com Redirected
Again on Thu, 30 May 91 14:41:20 +0100 To: Recipient MD
Assigned Alternate Recipient)in addition, the following per-recipient services from MTS.OtherMessageDeliveryFields.extensions get represented in comments if they're used 🌸. none of these services can be provided on RFC 822 networks, so in general these are informative strings attached to other MTS recipients 🥺. some have string values already defined. for the rest, the string value shall be chosen by the implementor 🛠️. and if the parameter has a default value, then no comment shall be inserted when the parameter has that default value 🙈. the full list (with the strings where they exist) is:
requested-delivery-method
physical-forwarding-prohibited
"(Physical Forwarding Prohibited)".
physical-forwarding-address-request
"(Physical Forwarding Address Requested)".
physical-delivery-modes
registered-mail-type
recipient-number-for-advice
physical-rendition-attributes
physical-delivery-report-request
"(Physical Delivery Report Requested)".
proof-of-delivery-request
"(Proof of Delivery Requested)".4.6.2.3. Delivery Report Generation 📬
if MTA.PerRecipientMessageTransferFields.per-recipient-indicators requires a positive delivery notification, the gateway shall generate it 🚀. the Supplementary Information shall be set to show that the report is gateway generated, and this info shall include the name of the gateway that made the report 🫡.
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 is what 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 are used to build MTS.MTSIdentifier.global-domain-identifier. MTS.MTSIdentifier.local-identifier is set to the 822.msg-id, including the braces "<" and ">" 💖. if that string is longer than MTS.ub-local-id-length (32), then it gets truncated to that length ✂️.
the reverse mapping is not used in this specification 🙅♀️. it would only apply where MTS.MTSIdentifier.local-identifier is of syntax 822.msg-id, and then it algorithmically identifies MTS.MTSIdentifier 🔁.
4.7. IPMS Mappings 💌
all RFC 822 addresses are assumed to use the 822.mailbox syntax 📮. that includes all 822.comments associated with the lexical tokens of the 822.mailbox 💬. in the IPMS, O/R Names are encoded as MTS.ORName 🧾. this gets used within IPMS.ORDescriptor, IPMS.RecipientSpecifier, and IPMS.IPMIdentifier 🎀. an asymmetrical mapping is defined between these components, so it's not a mirror image, and that's okay 🦋.
4.7.1. RFC 822 -> X.400 ✨
this section is about deriving IPMS.ORDescriptor from an RFC 822 address 🔮.
- take the address and extract an EBNF.822-address. this can be derived trivially from either the 822.addr-spec or 822.route-addr syntax 🧠. it's mapped to MTS.ORName as described above, and used as
IMPS.ORDescriptor.formal-name📍. - a string shall be built out of these (if they're present) 🧵:
- the 822.phrase component, if the 822.address is an 822.phrase 822.route-addr construct
- any 822.comments, in order, keeping the parentheses 🌷
this string then gets encoded into T.61, using a human oriented mapping (as described in Chapter 3) 📝. if the string isn't null, it's assigned to IPMS.ORDescriptor.free-form-name 💅.
IPMS.ORDescriptor.telephone-numberis omitted 🙈.
if IPMS.ORDescriptor is being used in IPMS.RecipientSpecifier, then IPMS.RecipientSpecifier.reply-request and IPMS.RecipientSpecifier.notification-requests are set to default values (none and false) 🌈.
if the 822.group construct is present, any included 822.mailbox is encoded as above to generate a separate IPMS.ORDescriptor 🧚. the 822.group is mapped to T.61, and an IPMS.ORDescriptor with only a free-form-name component gets 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, proceed as follows:
- encode
IPMS.ORDescriptor.formal-name(MTS.ORName) as EBNF.822-address 🧩. 2a. ifIPMS.ORDescriptor.free-form-nameis 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. ifIPMS.ORDescriptor.free-form-nameis absent: if EBNF.822-address is parsed as 822.addr-spec, use this as the encoding of 822.mailbox. if EBNF.822-address is parsed as 822.route 822.addr-spec, then a 822.phrase taken from 822.local-part gets added 🌸. - if
IPMS.ORDescriptor.telephone-numberis present, it's placed in an 822.comment with the string "Tel ". the normal international form of number is used. for example:
(Tel +44-1-387-7050)- if
IPMS.ORDescriptor.formal-name.directory-nameis present, a text representation is placed in a trailing 822.comment 📜. - if
IPMS.RecipientSpecifier.report-requesthas any non-default values, then an 822.comment "(Receipt Notification Requested)", and/or "(Non Receipt Notification Requested)", and/or "(IPM Return Requested)" gets appended to the address 📨. if both receipt and non-receipt notifications are requested, the comment for the latter may be omitted, to keep the RFC 822 address cleaner ✨. the effort of correlating P1 and P2 information is too great to justify the gateway sending Receipt Notifications 😤. - if
IPMS.RecipientSpecifier.reply-requestis True, an 822.comment "(Reply requested)" gets appended to the address 💬.
if IPMS.ORDescriptor.formal-name is absent, then IPMS.ORDescriptor.free-form-name is converted to ASCII and used as the 822.phrase within the RFC 822 822.group syntax 🧺. for example:
Free Form Name ":" ";"steps 3-6 are then 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 reference an RFC 822 Message ID, which is preferable to a gateway generated ID 🫶. a reversible and symmetrical mapping is defined, so good things happen when messages pass across the X.400/RFC 822 boundary multiple times 🦋.
an important issue with message identifiers is mapping to the exact form, because many systems use these ids as uninterpreted keys 🔑. table driven mappings aren't always symmetrical, especially with alternative domain names and alternative management domains 😵💫. so, a purely algorithmic mapping is used. a mapping that's simpler than the one for addresses can be used, for two reasons:
- there is no major requirement to make message IDs "natural" 🌿
- there is no issue about being able to reply to message IDs. (for addresses, creating a return path which works is more important than being symmetrical) 💌
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 defined so that the possibility 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 ✂️. the upper bound on this component is 64 📏. the options for handling this are discussed in Section 5.1.3 📖.
4.7.3.2. IPMS.IPMIdentifier represented in RFC 822 🎀
the 822.domain of 822.msg-id is set to the value "MHS" 💜. the 822.local-part of 822.msg-id is built as:
[ printablestring ] "*" [ std-or-address ]with EBNF.printablestring being the IPMS.IPMIdentifier.user-relative-identifier, and std-or-address being an encoding of the IPMS.IPMIdentifier.user 🧩. if necessary, the 822.quoted-string encoding is used 🫧. for example:
<"147*/S=Dietrich/O=Siemens/ADMD=DBP/C=DE/"@MHS>4.7.3.3. 822.msg-id -> IPMS.IPMIdentifier
okay so here's the vibe 💅 if the 822.local-part can be parsed like this:
[ printablestring ] "*" [ std-or-address ]and the 822.domain is "MHS", then this ID was X.400 generated ✨ If EBNF.printablestring is present, the value gets 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, it's 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 the IPMS.IPMIdentifier.user to generate an EBNF.std-or-address form string. Then build the 822.local-part of the 822.msg-id with the syntax:
[ printablestring ] "*" [ std-or-address ]The printablestring is taken from IPMS.IPMIdentifier.user-relative-identifier. Use 822.quoted-string if necessary. The 822.msg-id is generated with this 822.local-part, and "MHS" as the 822.domain 🎀
4.7.3.5. Phrase form
in "In-Reply-To:" and "References:", the encoding 822.phrase may be used as an alternative to 822.msg-id 🧚 To map from 822.phrase to IPMS.IPMIdentifier, assign IPMS.IPMIdentifier.user-relative-identifier to the phrase.
when mapping from IPMS.IPMIdentifier for "In-Reply-To:" and "References:", if IPMS.IPMIdentifier.user is absent and IPMS.IPMIdentifier.user-relative-identifier does not parse as 822.msg-id, generate an 822.phrase rather than adding the domain MHS. no cap, this is so specific 😭
4.7.3.6. RFC 987 backwards compatibility
ngl this part is giving drama 🙈 The mapping defined here is different to the one used in RFC 987, because the RFC 987 mapping led to changed message IDs in many cases. Fixing the problems is preferable to retaining backwards compatibility 👑 An implementation of this standard is encouraged to recognise message IDs generated by RFC 987. This is not required.
RFC 987 generated encodings may be recognised like this. When mapping from X.400 to RFC 822, if the IPMS.IPMIdentifier.user-relative-identifier is "RFC-822", the ID is RFC 987 generated. When mapping from RFC 822 to X.400, if the 822.domain is not "MHS", and the 822.local-part can be parsed as
[ printablestring ] "*" [ std-or-address ]then it is RFC 987 generated. In each of these cases, it is recommended to follow the RFC 987 rules 🌈
Chapter 5 - Detailed Mappings ✨
this chapter is where the detailed mappings live 🫶 It specifies detailed mappings for the functions outlined in Chapters 1 and 2. It makes extensive use of the notations and mappings defined in Chapters 3 and 4.
5.1. RFC 822 -> X.400
5.1.1. Basic Approach
a single IP Message is generated from an RFC 822 message 💅 The RFC 822 headers are used to generate the IPMS.Heading. The IP Message will have one IA5 IPMS.BodyPart containing the RFC 822 message body.
some RFC 822 fields can't be mapped onto a standard IPM Heading field, so an extended field is defined in Section 5.1.2. This is 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 are not in principle available to the MTS User. Use of these services allows RFC 822 MTA level parameters to be carried in the analogous X.400 service elements. The advantages of this mapping far outweigh the layering violation 🦋
5.1.2. X.400 Extension Field
an IPMS Extension is defined like so:
rfc-822-field HEADING-EXTENSION
VALUE RFC822FieldList
::= id-rfc-822-field-list
RFC822FieldList ::= SEQUENCE OF RFC822Field
RFC822Field ::= IA5StringThe Object Identifier id-rfc-822-field-list is defined in Appendix D.
to encode any RFC 822 Header using this extension, you build an RFC822Field element using the 822.field, omitting the trailing CRLF. For example, "Fruit-Of-The-Day: Kiwi Fruit". Structured fields shall be unfolded. There shall be no space before the ":". The reverse mapping builds the RFC 822 field in a straightforward manner. This RFC822Field is appended to the RFC822FieldList, which is added to the IPM Heading as an extension field 🍓
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's a "Comments:" field in the RFC 822 header.
if no specific 1988 features are used, the IPM generated is encoded as content type 2. Otherwise, it's encoded as content type 22. The latter will always be the case if extension heading fields are generated ✨
when generating the IPM, the issue of upper bounds must be considered 🙈 At the MTS and MTA level, this specification is strict about enforcing upper bounds. Three options are available at the IPM level. Use of any of these options conforms to this standard.
- 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 is likely to 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.
If the Free Form name is truncated, it may lead to breaking RFC 822 comments, which will cause an awkward reverse mapping.
these options have different advantages and disadvantages, and the choice will depend on the exact application of the gateway 🫶
the rest of this section is about IPMS.IPM.heading (IPMS.Heading). The only mandatory component of IPMS.Heading is the IPMS.Heading.this-IPM (IPMS.IPMIdentifier). A default is generated by the gateway. With the exception of "Received:", the values of multiple fields are merged (e.g. if there are two "To:" fields, then the mailboxes of both are merged to generate a single list which is used in the IPMS.Heading.primary-recipients). Information shall 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 toIPMS.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 toIPMS.Heading.authorizing-users. If not, it is mapped toIPMS.Heading.originator. For this, and other components containing addresses, the mappings of Chapter 4 are used for each address.Sender:: Mapped toIPMS.Heading.originator.Reply-To:: Mapped toIPMS.Heading.reply-recipients.To:: Mapped toIPMS.Heading.primary-recipients.Cc:: Mapped toIPMS.Heading.copy-recipients.Bcc:: Mapped toIPMS.Heading.blind-copy-recipientsif there is at least one BCC: recipient. If there are no recipients in this field, it should be mapped to a zero length sequence.In-Reply-To:: If there is one value, it is mapped toIPMS.Heading.replied-to-IPM, using the 822.phrase or 822.msg-id mapping as appropriate. If there are several values, they are mapped toIPMS.Heading.related-IPMs, along with any values from a "References:" field.References:: Mapped toIPMS.Heading.related-IPMs.Keywords:: Mapped onto a heading extension.Subject:: Mapped toIPMS.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, withIPMS.IA5TextBodyPart.parameters.repertoireset to the default (ia5), containing the value of the fields, preceded by the string "Comments: ". This body part shall 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 is applied to RFC 822 fields where the content of the field does not conform to RFC 822 (e.g. a Date: field with unparseable syntax).
5.1.4. Mappings to the MTS Abstract Service
the MTS.MessageSubmissionEnvelope comprises MTS.PerMessageSubmissionFields and MTS.PerRecipientMessageSubmissionFields. The mandatory parameters are 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 are omitted, and default components are defaulted. This means that disclosure of recipients is prohibited and conversion is allowed. There are two exceptions to the defaulting. For MTS.PerMessageSubmissionFields.per-message-indicators, the following settings are made:
- Alternate recipient is allowed, as it seems desirable to maximise the opportunity for (reliable) delivery.
- Content return request is set according to the issues discussed in Section 5.2.
MTS.PerMessageSubmissionFields.original-encoded-information-types is a set of one element, BuiltInEncodedInformationTypes.ia5-text 🎀
the MTS.PerMessageSubmissionFields.content-correlator is encoded as IA5String, and contains the Subject:, Message-ID:, Date:, and To: fields (if present). This includes the strings "Subject:", "Date:", "To:", "Message-ID:", and appropriate folding. This shall be truncated to MTS.ub-content-correlator-length (512) characters. In addition, if there is a "Subject:" field, the MTS.PerMessageSubmissionFields.content-identifier is set to a printable string representation of the contents of it. If the length of this string is greater than MTS.ub-content-id-length (16), it should be truncated to 13 characters and the string "..." appended. Both are used, due to the much larger upper bound of the content correlator, and because the content id is available in X.400(1984) 🌟
5.1.5. Mappings to the MTA Abstract Service 🧚
okay so this section is where we map straight onto some bits of the MTA Abstract service 💅 and we need it for a few reasons:
- 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, bestie 🎀
Message-Id: 💌 if this is present, MTA.PerMessageTransferFields.message-identifier gets generated from it, using the mappings from Chapter 4.
Date: 📅 this sets the first component of MTA.PerMessageTransferFields.trace-information (MTA.TraceInformationElement). The 822-MTS originator gets mapped into an MTS.ORAddress, and that's what derives MTA.TraceInformationElement.global-domain-identifier. The optional components of MTA.TraceInformationElement.domain-supplied-information get left out, and the mandatory ones are set like this:
MTA.DomainSuppliedInformation.arrival-time→ set to the date derived fromDate:MTA.DomainSuppliedInformation.routing-action→ set torelayed
The first element of MTA.PerMessageTransferFields.internal-trace-information is made in a similar way 🧚 although it can get dropped later in certain circumstances (see the procedures for "Received:"). MTA.InternalTraceInformationElement.mta-name is derived from the 822.domain in the 822 MTS Originator address.
Received: 📨 all the RFC 822 trace gets used to derive MTA.PerMessageTransferFields.trace-information and MTA.PerMessageTransferFields.internal-trace-information.
Processing of Received: lines follows processing of Date:, and it's done from the bottom to the top of the RFC 822 header (i.e., in chronological order). When other trace elements get processed (X400-Received: in all cases, and Via: if Appendix B is supported), the relative ordering SHALL be retained correctly 🫶 The initial element of MTA.PerMessageTransferFields.trace-information will already be generated (from Date:), unless the message has previously been in X.400. In that case it gets derived from the X.400 trace information.
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 SHALL be done in cases where the message is being transferred to another MD that has no bilateral agreement to preserve internal trace beyond the local MD. The trace creation works like the 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 is set to the value derived. The MTA.InternalTraceInformationElement.mta-supplied-information (MTA.MTASuppliedInformation) is set as follows:
MTA.MTASuppliedInformation.arrival-time→ derived from the date of theReceived:lineMTA.MTASuppliedInformation.routing-action→ set torelayed
MTA.InternalTraceInformationElement.mta-name is 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 GMTThis generates the string:
vs6.Cs.Ucl.AC.UK⚠️ bestie, before transferring the message to some ADMDs, you may need extra trace stripping, because the implied path through multiple MDs would break ADMD policy. Whether you need it depends on the bilateral agreement with that ADMD 🙈
5.1.6. Mapping New Fields 🎀
this spec defines a bunch of new fields for Reports, Notifications and IP Messages in Section 5.3. But since this spec only aims to preserve existing services, a gateway that conforms to it doesn't have to map all of these fields to X.400 ✨
Two extended fields MUST be mapped, to prevent looping 🔁 DL-Expansion-History: is mapped to MTA.PerMessageTransferFields.extensions.dl-expansion-history. X400-Received: MUST be mapped to MTA.PerMessageTransferFields.trace-information and MTA.PerMessageTransferFields.internal-trace-information. When X400-Received: is present, the usual mapping of Date: to generate the first element of trace SHOULD NOT be done 🙅♀️ That's because the message came from X.400, so the first element of trace can be taken from the first X400-Received:.
Some fields SHALL NOT be mapped, and SHOULD be discarded 🗑️ The following cannot be mapped back:
Discarded-X400-MTS-Extensions:Message-Type:Discarded-X400-IPMS-Extensions:
If Message-Type: is set to "Multiple Part", then the message is encoded according to RFC 934, and this may be mapped on to the corresponding X.400 structures.
The following may cause problems, because other information doesn't get mapped back (e.g., extension numbers), or because of changes made on the RFC 822 side from list expansion 😬
X400-Content-Type:X400-Originator:X400-Recipients:X400-MTS-Identifier:
Other fields MAY be either discarded or mapped to X.400. It's usually desirable and beneficial to do the mapping, especially to help a message that travels through multiple gateways 🌈 These mappings MAY be onto MTA, MTS, or IPMS services. The level of support for this reverse mapping SHOULD be indicated in the gateway conformance statement 📝
5.2. Return of Contents 📬
it's not clear how widely supported the X.400 return of contents service will be 🤷♀️ Experience with X.400(1984) suggests that support for this service may not be universal. Since this service is expected in the RFC 822 world, two approaches are specified. Which one you use depends on how the X.400 community served by the gateway uses X.400 return of contents.
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 way 💖
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, the content return request will not be requested, and the 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 SHALL 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 alongside 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's no appropriate existing field, new fields are defined for IPMS, MTS and MTA services.
The gateway mechanisms will correspond to MTS Delivery. Like with submission, the MTA (transfer) services are also used in some places. In particular, there's an optimisation that allows for multiple 822-MTS recipients 🧠
5.3.2. RFC 822 Settings 🌸
An RFC 822 Service needs a number of mandatory fields in the RFC 822 Header. Some 822-MTS services require specifying an 822-MTS Originator. Even when that's optional, it's usually desirable to specify a value 💅 The following defaults are defined, which SHALL be used if the specified mappings don't 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 SHALL be assigned.
Date:: A value will always be generated.From:: If this is not generated by the mapping, it is assigned equal to the 822-MTS Originator. If this is gateway generated, an appropriate 822.phrase SHALL be added.- At least one recipient field: If no recipient fields are generated, a field
To: list:;SHALL be added.
This keeps things at minimal RFC 822 compliance 🫶 When generating RFC 822 headers, folding MAY be used. It is RECOMMENDED to do this, following the guidelines of RFC 822 🎀
5.3.3. Basic Mappings 🧚
5.3.3.1. Encoded Information Types 💜
This mapping from MTS.EncodedInformationTypes is needed in several disconnected places. Here's the EBNF:
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, now we're mapping an IPM over to RFC 822 🦋 An IPM is made of an IPMS.IPM.heading and an IPMS.IPM.body, and we do the heading first. There's some EBNF for the brand-new fields, so here it is 💅
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"Every heading element gets its own mapping and action now. Addresses and Message Identifiers are mapped according to Chapter 4. The other mappings are either explained or totally straightforward (algorithmic) 🎀 If a field with addresses has zero elements, it SHOULD be discarded, except for IPMS.Heading.blind-copy-recipients. That one can be mapped onto BCC:, because it's the only RFC 822 field that's allowed to have zero recipients 🙈
IPMS.Heading.this-IPM: Mapped toMessage-ID:.IPMS.Heading.originator: IfIPMS.Heading.authorizing-usersis present, this gets mapped toSender:. If not, it goes 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 get converted to ASCII (as defined in Chapter 3). Any CRLF doesn't get mapped, but it's used as a spot 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) get mapped like this:
incomplete-copy: Mapped to the extended RFC 822 fieldIncomplete-Copy:.language: Mapped to the extended RFC 822 fieldLanguage:, with the two letter code filled in. Thelanguage-descriptionMAY be filled in with a human readable description of the language, and it is RECOMMENDED to do this 🌈
If the RFC 822 extended header is found, it SHALL be mapped onto an RFC 822 header, as described in Section 5.1.2 🦋
If a non-standard extension shows up, it SHALL be discarded, unless the gateway understands that extension and can do an appropriate mapping onto an RFC 822 header field 💅 If extensions do get discarded, the list gets noted in the extended RFC 822 field Discarded-X400-IPMS-Extensions: 🧚
Next up is the body. The IPMS.Body gets mapped into the RFC 822 message body, and each IPMS.BodyPart gets converted to ASCII like this:
IPMS.IA5Text: The mapping is straightforward (see Chapter 3).IPMS.MessageBodyPart: The X.400 -> RFC 822 mapping gets applied recursively, to generate an RFC 822 Message. If it's present,IPMS.MessageBodyPart.parameters.delivery-envelopeis used for the MTS Abstract Service Mappings. If it's present,IPMS.MessageBodyPart.parameters.delivery-timeis mapped to the extended RFC 822 fieldDelivery-Date:✨Other: If other body parts can be mapped to IA5, either through the mappings defined in X.408 [CCITT88a] or through other reasonable mappings, this SHALL be done unless content conversion is prohibited 🎀
If some or all of the body parts can't be converted, there are three options. All of these conform to this standard. A different choice MAY be made for the case where no body part can be converted 🙈
- 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 in this style:
*********************************
There was a foobarhere
The widget gateway ate it
*********************************This lets some useful information get through. Since the recipient is likely to be a human (IPMS), suitable action will usually be possible 💖
- Finally, both MAY be done. In this case, the supplementary information in the (positive) Delivery Report SHALL make clear that something was sent on to the recipient with substantial loss of information 😭
If there's more than one IPMS.BodyPart, the mapping defined by Rose and Stefferud in [Rose85a] gets used to map the separate IPMS.BodyParts into the single RFC 822 message body. When that happens, a Message-Type: field with the value Multiple part SHALL be added. That tells a receiving gateway that the message MAY be unfolded according to RFC 934 🫶
Note: There's currently work going on to upgrade RFC 934, which also supports body parts with non-ASCII content (MIME). When that work is released as an RFC, this specification will be updated to refer to it instead of RFC 934 🔥
For backwards compatibility with RFC 987, the following procedures SHALL also be followed. If there are two IA5 body parts, and the first one starts with the string RFC-822-Headers: as its first line, then the rest of that body part SHALL be appended to the RFC 822 header 🌸
An example message, showing off a bunch of these aspects, is below 👑
Return-Path:<@mhs-relay.ac.uk:stephen.harrison@gosip-uk.hmg.gold-400.gb>
Received: from mhs-relay.ac.uk by bells.cs.ucl.ac.uk via JANET
with NIFTP id <7906-0@bells.cs.ucl.ac.uk>;
Thu, 30 May 1991 18:24:55 +0100
X400-Received: by mta "mhs-relay.ac.uk" in
/PRMD=uk.ac/ADMD= /C=gb/; Relayed;
Thu, 30 May 1991 18:23:26 +0100
X400-Received: by /PRMD=HMG/ADMD=GOLD 400/C=GB/; Relayed;
Thu, 30 May 1991 18:20:27 +0100
Message-Type: Multiple Part
Date: Thu, 30 May 1991 18:20:27 +0100
X400-Originator: Stephen.Harrison@gosip-uk.hmg.gold-400.gb
X400-MTS-Identifier:
[/PRMD=HMG/ADMD=GOLD 400/C=GB/;PC1000-910530172027-57D8]
Original-Encoded-Information-Types: ia5, undefined
X400-Content-Type: P2-1984 (2)
Content-Identifier: Email Problems
From: Stephen.Harrison@gosip-uk.hmg.gold-400.gb (Tel +44 71 217 3487)
Message-ID: <PC1000-910530172027-57D8*@MHS>
To: Jim Craigie <NTIN36@gec-b.rutherford.ac.uk>
(Receipt Notification Requested) (Non Receipt Notification Requested),
Tony Bates <tony@ean-relay.ac.uk> (Receipt Notification Requested),
Steve Kille <S.Kille@cs.ucl.ac.uk> (Receipt Notification Requested)
Subject: Email Problems
Sender: Stephen.Harrison@gosip-uk.hmg.gold-400.gb
------------------------------ Start of body part 1
Hope you gentlemen.......
Regards,
Stephen Harrison
UK GOSIP Project
------------------------------ Start of forwarded message 1
From: Urs Eppenberger <Eppenberger@verw.switch.ch>
Message-ID:
<562*/S=Eppenberger/OU=verw/O=switch/PRMD=SWITCH/ADMD=ARCOM/C=CH/@MHS>
To: "Stephen.Harrison" <Stephen.Harrison@gosip-uk.hmg.gold-400.gb>
Cc: kimura@bsdarc.bsd.fc.nec.co.jp
Subject: Response to Email link
- ------------------------------ Start of body part 1
Dear Mr Harrison......
- ------------------------------ End of body part 1
------------------------------ End of forwarded message 15.3.5. Mappings from an IP Notification ✨
okay so first up, we build a message with these fields 💌
From:gets set to the IPMS.IPN.ipn-originator.To:gets set to the recipient from MTS.MessageSubmissionEnvelope. If there have been redirects, the original address should be used. 🦋Subject:gets set to"X.400 Inter-Personal Notification"for a receipt notification, and to"X.400 Inter-Personal Notification (failure)"for a non-receipt notification. 💅Message-Type:gets set to"InterPersonal Notification"🎀References:gets set to IPMS.IPN.subject-ipm 🫶
Now the body. This EBNF is defined so that all the info from an interpersonal notification reaches the end user in one uniform way, no chaos 🌈
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
discard-reason = "Expired" / "Obsoleted" /
"User Subscription Terminated"
acknowledgement-mode = "Manually" / "Automatically"Next, the IPMS.CommonFields bits of IPMS.IPN map onto that structure and the message header like this 🧚
subject-ipmgoes toReferences:ipn-originatorgoes toFrom:ipn-preferred-recipientgoes to EBNF.preferred-recipientconversion-eitsgoes to EBNF.encoded-info inside EBNF.ipn-extra-information
For IPMS.IPN.non-receipt-fields (IPMS.NonReceiptFields):
non-receipt-reasonis used to pick between EBNF.ipn-discarded and EBNF.ipn-auto-forwardeddiscard-reasongoes to EBNF.discard-reasonauto-forward-commentgoes to EBNF.auto-commentreturned-ipmonly applies to non-receipt notifications. EBNF.ipn-content-return should always be omitted for receipt notifications, and always be present in non-receipt notifications. If it is present, the second option of EBNF.ipn-content-return is chosen and an RFC 822 mapping of the message is included. Otherwise the first option is chosen. 🙈
And for IPMS.IPN.receipt-fields (IPMS.ReceiptFields):
receipt-timegoes to EBNF.receipt-timeacknowledgement-modegoes to EBNF.acknowledgement-modesuppl-receipt-infogoes to EBNF.ipn-suppl
Here's an example notification, verbatim, so you can see how it all lands 👀
From: Steve Kille <steve@cs.ucl.ac.uk>
To: Julian Onions <jpo@computer-science.nottingham.ac.uk>
Subject: X.400 Inter-personal 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: g3fax5.3.6. Mappings from the MTS Abstract Service ✨
okay this section is the MTS mappings for User Messages (IPM and IPN) 📬 The mapping is defined by specifying how MTS.MessageDeliveryEnvelope gets mapped. To make it work, these extensions to RFC 822 are defined:
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 ";"
/ "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"Now let's go through each element of MTS.MessageDeliveryEnvelope 💖
MTS.MessageDeliveryEnvelope.message-delivery-identifiermaps to the extended RFC 822 fieldX400-MTS-Identifier:MTS.MessageDeliveryEnvelope.message-delivery-timeis discarded, since this time gets represented in an appropriate trace element ⏰
For the elements of MTS.MessageDeliveryEnvelope.other-fields (MTS.OtherMessageDeliveryFields):
content-typemaps to the extended RFC 822 fieldX400-Content-Type:. The string"P2"is kept for backwards compatibility with RFC 987. It shall not be generated, and either the EBNF.labelled-integer or EBNF.object-identifier encoding is used instead. 🌸originator-namemaps to the 822-MTS originator and to the extended RFC 822 fieldX400-Originator:. This is described in Section 4.6.2.original-encoded-information-typesmaps to the extended RFC 822 fieldOriginal-Encoded-Information-Types:prioritymaps 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-names, plusoriginally-intended-recipient-name: these are handled as described in Section 4.6.2.converted-encoded-information-typesis discarded, as it will always be IA5 only.message-submission-timemaps toDate:content-identifiermaps to the extended RFC 822 fieldContent-Identifier:
⚠️ If any extensions (MTS.MessageDeliveryEnvelope.other-fields.extensions) are present, and they are marked as critical for transfer or delivery, then the message shall be rejected. Otherwise, the extensions are mapped as follows.
conversion-with-loss-prohibited: if it is set to MTS.ConversionWithLossProhibited.conversion-with-loss-prohibited, add the extended RFC 822 fieldConversion-With-Loss:requested-delivery-methodmaps to the extended RFC 822 fieldRequested-Delivery-Method:originator-return-addressmaps to the extended RFC 822 fieldOriginator-Return-Address:physical-forwarding-address-request,physical-delivery-modes,registered-mail-type,recipient-number-for-advice,physical-rendition-attributes,physical-delivery-report-request, andphysical-forwarding-prohibitedare only appropriate for physical delivery. They are represented as comments in theX400-Recipients:field, as described in Section 4.6.2.2. 📦originator-certificate,message-token,content-confidentiality-algorithm-identifier,content-integrity-check,message-origin-authentication-check,message-security-label, andproof-of-delivery-requestimply use of security services that aren't available in the RFC 822 environment. If they are marked as critical for transfer or delivery, then the message shall be rejected. Otherwise they are discarded. 🔐redirection-historyis described in Section 4.6.2.dl-expansion-history: each element maps to the extended RFC 822 fieldDL-Expansion-History:. They shall be ordered in the message header so that the most recent expansion comes first (same order as trace). 🧾
Last bit: if any MTS (or MTA) Extensions not specified in X.400 are present, and they are marked as critical for transfer or delivery, then the message shall be rejected. If they are not marked that way, they can safely be discarded. The list of discarded fields shall be indicated in the extended header Discarded-X400-MTS-Extensions:. 🫧
5.3.7. Mappings from the MTA Abstract Service ✨
Okay bestie, so there are some mappings that happen at the MTA Abstract Service level, and they're for both IPM and IPN 💌. You can figure all of them out from MTA.MessageTransferEnvelope. This is where it gets a bit spicy because it breaks layering 🙈, but there are three reasons for doing it:
- Allowing for multiple recipients to share a single RFC 822 message
- Making the X.400 trace information available on the RFC 822 side
- Making any information on deferred delivery available
The 822-MTS recipients get worked out from the full list of X.400 recipients 📬. That's every member of MTA.MessageTransferEnvelope.per-recipient-fields being passed through the gateway where the responsibility bit is set. Sometimes each recipient ends up with a different RFC 822 message because they asked for different services 💅. As discussed in 4.6.2..2, this specification allows either for multiple messages to be generated, or for the per-recipient information to be discarded.
Here's the EBNF for the 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-or-mta ";" ]
action-list
";" arrival-time
md-and-mta = [ "mta" mta "in" ] global-id
mta = word
arrival-time = date-time
md-or-mta = "MD" global-id
/ "MTA" mta
Action-list = 1#action
action = "Redirected"
/ "Expanded"
/ "Relayed"
/ "Rerouted"Note the EBNF.mta is encoded as 822.word. If the character set does not allow encoding as 822.atom, the 822.quoted-string encoding is used.
If MTA.PerMessageTransferFields.deferred-delivery-time is present, it gets used to generate a Deferred-Delivery: field. For some reason, X.400 doesn't make this info available at the MTS level on delivery 🤷♀️. X.400 profiles, and in particular the CEN/CENELEC profile for X.400(1984) [Systems85a], say this element must be supported at the first MTA. If it isn't, the function may optionally be implemented by the gateway, which means the gateway may hold the message until the time specified in the protocol element. So the value of this element will usually be in the past 🕰️. For this reason, the extended RFC 822 field is primarily for information.
Now merge MTA.PerMessageTransferFields.trace-information and MTA.PerMessageTransferFields.internal-trace-information into one ordered trace list 🧵. If internal trace from other management domains hasn't been stripped, this may get a bit messy with complex interleaving. Where an element of internal trace and external trace are identical, except for the MTA in the internal trace, only the internal trace element shall be presented. Use that to generate a sequence of "X400-Received:" fields. The only difference between external trace and internal trace will be the extra MTA info in the internal trace elements.
When generating an RFC 822 message, all trace fields (X400-Received and Received) shall be at the beginning of the header, before any other fields. Trace shall be in chronological order, with the most recent element at the front of the message. This ordering comes from the order of the fields, not from timestamps in the trace, because there's no guarantee of clock synchronisation ⏰. 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 here's a more complex example (internal) 🧩:
X400-Received: by mta "UK.AC.UCL.CS"
in /PRMD=UK.AC/ADMD=Gold 400/C=GB/ ;
deferred until Tue, 20 Jun 89 14:24:22 +0100 ;
converted (undefined, g3fax) ";" attempted /ADMD=Foo/C=GB/ ;
Relayed, Expanded, Redirected ; Tue, 20 Jun 89 19:25:11 +01005.3.8. Mappings from Report Delivery 📨
Delivery reports get mapped at the MTS service level, which means only reports destined for the MTS user will be mapped 🎯. Some additional services are also taken from the MTA service.
5.3.8.1. MTS Mappings 🎀
okay so a Delivery Report service is represented as MTS.ReportDeliveryEnvelope 📮, which is made up of per-report-fields (MTS.PerReportDeliveryFields) and per-recipient-fields. ✨
A message gets generated with these fields:
From:an administrator at the gateway system. This is also the 822-MTS originator. 💅To:a mapping of theMTA.ReportTransferEnvelope.report-destination-name. This is also the 822-MTS recipient. 🦋Message-Type:set to "Delivery Report". 🌸Subject:the EBNF for the subject line is:
subject-line = "Delivery-Report" "(" status ")"
[ "for" destination ]
status = "success" / "failure" / "success and failures"
destination = mailbox / "MTA" wordThe body is set up so that everything reaches the RFC 822 user in a consistent way 💖. It's structured like a message coming from X.400, with the description in one body part and a forwarded message (return of content) in the second. This is super useful for the RFC 822 recipient because it means the original message can be pulled out. 🧚 The first body part is laid out like this:
- A few lines giving keywords to indicate the original message.
- A human summary of the status of each recipient being reported on.
- A clearly marked section which contains detailed information extracted from the report. This is marked clearly, as it will not be comprehensible to the average user. It is retained, as it may be critical to diagnosing an obscure problem.
This section may be omitted in positive DRs, and it is recommended that this is appropriate for most gateways. 🍓
dr-body-format = dr-summary <CRLF>
dr-recipients <CRLF>
dr-administrator-info-envelope <CRLF>
dr-content-return
dr-content-return = "The Original Message is not available"
/ "The Original Message follows:"
dr-summary = "This report relates to your message:" <CRLF>
content-correlator <CRLF> <CRLF>
"of" 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-administrator-info-envelope = 3*( "*" text <CRLF> )
dr-administrator-info =
"**** The following information is directed towards"
"the local administrator" <CRLF>
"**** and is not intended for the end user" <CRLF> <CRLF>
"DR generated by:" report-point <CRLF>
"at" date-time <CRLF> <CRLF>
"Converted to RFC 822 at" mta <CRLF>
"at" date-time <CRLF> <CRLF>
"Delivery Report Contents:" <CRLF> <CRLF>
drc-field-list <CRLF>
"***** End of administration information"
drc-field-list = *(drc-field <CRLF>)
drc-field = "Subject-Submision-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 outer level is a fixed definition, EBNF.dr-body-format. ✨ The element EBNF.dr-administrator-info-envelope gives you a way to wrap a section of the header in a manner that's clear to the end user. 🫶 Each line of this section begins with "". Each element of EBNF.text within %EBNF.dr-administrator-info-envelope must not contain <CRLF>. This is used to wrap up EBNF.dr-administrator-info, which will generate a sequence of lines not starting with "". EBNF.drc-fields may be folded using the RFC 822 folding rules. 🌈
The elements of MTS.ReportDeliveryEnvelope.per-report-fields are mapped onto extended RFC 822 fields like this:
subject-submission-identifieris mapped toEBNF.drc-field(Subject-Submission-Identifier). 🎀content-identifieris mapped toEBNF.drc-field(Content-Identifier). This should also be used inEBNF.dr-summaryif there is no Content Correlator present. 🦋content-typeis mapped toEBNF.drc-field(Content-Type). 🌸original-encoded-information-typesis mapped toEBNF.drc-field(Encoded-Info). 💜
The extensions from MTS.ReportDeliveryEnvelope.per-report-fields.extensions are mapped like this:
originator-and-DL-expansion-historyis mapped toEBNF.drc-field(Originator-and-DL-Expansion-History). 🍓reporting-DL-nameis mapped toEBNF.drc-field(Reporting-DL-Name). 🧚content-correlatoris mapped toEBNF.content-correlator, provided that the encoding is IA5String (this will always be the case). This is used inEBNF.dr-summaryandEBNF.drc-field-list. In the former, LWSP may be added, in order to improve the layout of the message. ✨message-security-label,reporting-MTA-certificateandreport-origin-authentication-check🔐
These security parameters will not be present unless there is an error in a remote MTA. If they are present, they shall be discarded in preference to discarding the whole report. 🙈
For each element of MTS.ReportDeliveryEnvelope.per-recipient-fields, a value of EBNF.dr-recipient and an EBNF.drc-field (Recipient-Info) is generated. The components are mapped as follows:
actual-recipient-nameis used to generate the firstEBNF.mailboxandEBNF.std-orinEBNF.recipient-info. Both RFC 822 and X.400 forms are given, as there may be a problem in the mapping tables. It also generates theEBNF.mailboxinEBNF.dr-recip-successorEBNF.dr-recip-failure. 💖report: if it isMTS.Report.delivery, then setEBNF.dr-recipienttoEBNF.dr-recip-success, and similarly setEBNF.report-type, filling inEBNF.drc-success. If it is a failure, setEBNF.dr-recipienttoEBNF.dr-recip-failure, making a human interpretation of the reason and diagnostic codes, and including any supplementary information.EBNF.drc-failureis filled in systematically. 🔥converted-encoded-information-types: setEBNF.drc-field("converted eits"). 🌷originally-intended-recipient: set the second ("originally intended recipient") mailbox and std-or inEBNF.drc-field. 🦄supplementary-info: setEBNF.drc-field("supplementary info"), and include this information inEBNF.dr-recip-failure. 🫧redirection-history: setEBNF.drc-field("redirection history"). 🌸physical-forwarding-address: setENBF.drc-field("physical forwarding address"). 🦋recipient-certificate: discard. 🗑️proof-of-delivery: discard. 🗑️
Any unknown extensions shall be discarded, irrespective of criticality. no exceptions, bestie 💅
The original message, or an extract from it, shall be included in the delivery port if it is available. The original message will usually be available at the gateway, as discussed in Section 5.2. If the original message is available but of erroneous format, a dump of the ASN.1 may be included. This is recommended, but not required. 🧚
5.3.8.2. MTA Mappings 🌸
The single 822-MTS recipient is constructed from MTA.ReportTransferEnvelope.report-destination-name, using the mappings of Chapter 4. Unlike with a user message, this information is not available at the MTS level. 🫶
The following additional mappings are made:
MTA.ReportTransferEnvelope.report-destination-nameis used to generate the To: field. 💜MTA.ReportTransferEnvelope.identifieris mapped 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-informationare mapped onto the extended RFC 822 field "X400-Received:", as described in Section 5.3.7. The first element is also used to generate the "Date:" field, and theEBNF.report-point. 🌈MTA.PerRecipientReportTransferFields.last-trace-informationis mapped toEBNF.recipient-info(last trace). ✨MTA.PerReportTransferFields.subject-intermediate-trace-informationis mapped toEBNF.drc-field(Subject-Intermediate-Trace-Information). These fields are ordered so that the most recent trace element comes first. 👑
5.3.8.3. Example Delivery Reports 🦋
Example Delivery Report 1: 🍓
Return-Path: <postmaster@cs.ucl.ac.uk>
Received: from cs.ucl.ac.uk by bells.cs.ucl.ac.uk
via Delivery Reports Channel id <27699-0@bells.cs.ucl.ac.uk>;
Thu, 7 Feb 1991 15:48:39 +0000
From: UCL-CS MTA <postmaster@cs.ucl.ac.uk>
To: S.Kille@cs.ucl.ac.uk
Subject: Delivery Report (failure) for H.Hildegard@bbn.com
Message-Type: Delivery Report
Date: Thu, 7 Feb 1991 15:48:39 +0000
Message-ID: <"bells.cs.u.694:07.01.91.15.48.34"@cs.ucl.ac.uk>
Content-Identifier: Greetings.
------------------------------ Start of body part 1
This report relates to your message: Greetings.
of Thu, 7 Feb 1991 15:48:20 +0000
Your message was not delivered to
H.Hildegard@bbn.com for the following reason:
Bad Address
MTA 'bbn.com' gives error message (USER) Unknown user
name in "H.Hildegard@bbn.com"
***** The following information is directed towards the local
***** administrator and is not intended for the end user
*
* DR generated by mta bells.cs.ucl.ac.uk
* in /PRMD=uk.ac/ADMD=gold 400/C=gb/
* at Thu, 7 Feb 1991 15:48:34 +0000
*
* Converted to RFC 822 at bells.cs.ucl.ac.uk
* at Thu, 7 Feb 1991 15:48:40 +0000
*
..... continued on next page
* Delivery Report Contents:
*
* Subject-Submission-Identifier:
* [/PRMD=uk.ac/ADMD=gold 400/C=gb/;<1803.665941698@UK.AC.UCL.CS>]
* Content-Identifier: Greetings.- Subject-Intermediate-Trace-Information: /PRMD=uk.ac/ADMD=gold 400/C=gb/;
- arrival Thu, 7 Feb 1991 15:48:20 +0000 action Relayed
- Subject-Intermediate-Trace-Information: /PRMD=uk.ac/ADMD=gold 400/C=gb/;
- arrival Thu, 7 Feb 1991 15:48:18 +0000 action Relayed
- Recipient-Info: H.Hildegard@bbn.com,
- /RFC-822=H.Hildegard(a)bbn.com/OU=cs/O=ucl /PRMD=uk.ac/ADMD=gold 400/C=gb/;
- FAILURE reason Unable-To-Transfer (1);
- diagnostic Unrecognised-ORName (0);
- last trace (ia5) Thu, 7 Feb 1991 15:48:18 +0000;
- supplementary info "MTA 'bbn.com' gives error message (USER)
- Unknown user name in "H.Hildegard@bbn.com""; ** End of administration information
The Original Message follows:
------------------------------ Start of forwarded message 1
Received: from glenlivet.cs.ucl.ac.uk by bells.cs.ucl.ac.uk with SMTP inbound id <27689-0@bells.cs.ucl.ac.uk>; Thu, 7 Feb 1991 15:48:21 +0000 To: H.Hildegard@bbn.com Subject: Greetings. Phone: +44-71-380-7294 Date: Thu, 07 Feb 91 15:48:18 +0000 Message-ID: <1803.665941698@UK.AC.UCL.CS> From: Steve Kille <S.Kille@cs.ucl.ac.uk>
Steve
------------------------------ End of forwarded message 1 Example Delivery Report 2:
Return-Path: <postmaster@cs.ucl.ac.uk> Received: from cs.ucl.ac.uk by bells.cs.ucl.ac.uk via Delivery Reports Channel id <27718-0@bells.cs.ucl.ac.uk>; Thu, 7 Feb 1991 15:49:11 +0000 X400-Received: by mta bells.cs.ucl.ac.uk in /PRMD=uk.ac/ADMD=gold 400/C=gb/; Relayed; Thu, 7 Feb 1991 15:49:08 +0000 X400-Received: by /PRMD=DGC/ADMD=GOLD 400/C=GB/; Relayed; Thu, 7 Feb 1991 15:48:40 +0000 From: UCL-CS MTA <postmaster@cs.ucl.ac.uk> To: S.Kille@cs.ucl.ac.uk Subject: Delivery Report (failure) for j.nosuchuser@dle.cambridge.DGC.gold-400.gb Message-Type: Delivery Report Date: Thu, 7 Feb 1991 15:49:11 +0000 Message-ID: <"DLE/910207154840Z/000"@cs.ucl.ac.uk> Content-Identifier: A useful mess...
This report relates to your message: A useful mess... Your message was not delivered to j.nosuchuser@dle.cambridge.DGC.gold-400.gb for the following reason: Bad Address DG 21187: (CEO POA) Unknown addressee.
* The following information is directed towards the local * administrator and is not intended for the end user *
- DR generated by /PRMD=DGC/ADMD=GOLD 400/C=GB/
- at Thu, 7 Feb 1991 15:48:40 +0000 *
- Converted to RFC 822 at bells.cs.ucl.ac.uk
- at Thu, 7 Feb 1991 15:49:12 +0000 *
- Delivery Report Contents: *
- Subject-Submission-Identifier:
- [/PRMD=uk.ac/ADMD=gold 400/C=gb/;<1796.665941626@UK.AC.UCL.CS>]
- Content-Identifier: A useful mess...
- Recipient-Info: j.nosuchuser@dle.cambridge.DGC.gold-400.gb,
- /I=j/S=nosuchuser/OU=dle/O=cambridge/PRMD=DGC/ADMD=GOLD 400/C=GB/;
- FAILURE reason Unable-To-Transfer (1);
- diagnostic Unrecognised-ORName (0);
- supplementary info "DG 21187: (CEO POA) Unknown addressee."; ** End of administration information
The Original Message is not available
### 5.3.9. Probe ✨
okay so this one is an MTS internal issue 🫶 any probe shall be serviced by the gateway, because there is literally no RFC 822 version of it 💀 The reply's vibe depends on whether the gateway could service an MTS Message using the values in the probe. And the reply shall make use of `MTS.SupplementaryInformation` to show that the probe was serviced by the gateway 🎀
# Appendix A - Mappings Specific to SMTP ✨
This appendix is specific to the Simple Mail Transfer Protocol (RFC 821) 🌸 It's all about the changes for this protocol. When servicing a probe, as described in section 5.3.9, use may be made of the SMTP `VRFY` command 💅 to increase the accuracy of the information in the delivery report 🔥
# Appendix B - Mappings specific to the JNT Mail ✨
This appendix is specific to the JNT Mail Protocol 🎀 It describes specific changes in the context of this protocol.
## 1. Introduction
There are five aspects of a gateway that are **JNT Mail Specific** 👑 Each one gets its own section of this appendix 💖
## 2. Domain Ordering
When interpreting and generating domains, the UK NRS domain ordering shall be used 🌍 both in headers, and in text generated for human description.
## 3. Addressing
A gateway which maps to JNT Mail should recognise the Domain Defined Attribute `JNT-MAIL` 🦋 The value associated with this attribute should be interpreted according to the JNT Mail Specification. This DDA shall never be generated by a gateway. For this reason, the overflow mechanism is not required 🙈
## 4. Acknowledge-To:
This field has no direct functional equivalent in X.400 😭 However, it can be supported to an extent, and it can be used to improve X.400 support 💜
If an `Acknowledge-To:` field is present when going from JNT Mail to X.400, there are two different situations 👀 The first case is where there is one address in the `Acknowledge-To:` field, and it is equal to the 822-MTS return address. In this case, the `MTS.PerRecipientSubmissionFields.originator-request-report.report` shall be set for each recipient, and the `Acknowledge-To:` field discarded. Here, X.400 can provide the equivalent service ✨
In all other cases two actions are taken.
1. Acknowledgement(s) may be generated by the gateway. The text of these acknowledgements shall indicate that they are generated by the gateway, and do not correspond to delivery.
2. The `Acknowledge-To:` field shall be passed as an extension heading.
When going from X.400 to JNT Mail, in cases where `MTA.PerRecipientMessageTransferFields.per-recipient-indicators.originator-report` bit is set for all recipients (i.e., there is a user request for a positive delivery report for every recipient), generate an `Acknowledge-To:` field containing the `MTS.OtherMessageDeliveryFields.originator-name` 🔥 Receipt notification requests are not mapped onto `Acknowledge-To:`, as no association can be guaranteed between IPMS and MTS level addressing information 💀
## 5. 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 is used. The trace text, including the "Via:", is 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 🫶
## 6. Timezone specification
The extended syntax of zone defined in the JNT Mail Protocol shall be used in the mapping of `UTCTime` defined in Chapter 3 🌸
## 7. Lack of 822-MTS originator specification
In JNT Mail the default mapping of the `MTS.OtherMessageDeliveryFields.originator-name` is to the `Sender:` field 💅 This can cause a problem when going from X.400 to JNT Mail if the mapping of `IPMS.Heading` has already generated a `Sender:` field 😭 To fix that, a new extended JNT Mail field is defined ✨ It is chosen to align with the JNT recommendation for interworking with full RFC 822 systems [Kille84b].
original-sender = "Original-Sender" ":" mailbox
If an IPM has no `IPMS.Heading.authorizing-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 an `IPMS.Heading.authorizing-users` component, and `IPMS.Heading.originator.formal-name` is different from `MTS.OtherMessageDeliveryFields.originator-name`, then `MTS.OtherMessageDeliveryFields.originator-name` is mapped onto the `Sender:` field, and `IPMS.Heading.originator` is 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 Smith
might be expressed from UUCP as
inthop!gate!gatehost.COM!/C=US/O=Xerox/PN=John.Smith/
(assuming gate is a UUCP-ARPA gateway and gatehost.COM is an ARPA-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 ARPA
Organisation GateOrg
RFC-822 inthop!dest!user@gatehost.COM
or through a single X.400 to UUCP gateway:
Country US
ADMD ATT
PRMD UUCP
Organisation GateOrg
RFC-822 inthop!dest!user
# Appendix D - Object Identifier Assignment ✨
An object identifier is needed for the extension IPMS element 🧚 The following value shall be used.
rfc-987-88 OBJECT IDENTIFIER ::=
{ccitt data(9) pss(2342) ucl(234219200300) rfc-987-88(200)}
id-rfc-822-field-list OBJECT IDENTIFIER ::= {rfc987-88 field(1)}
# Appendix E - BNF Summary ✨
Here is the BNF summary 💅
boolean = "TRUE" / "FALSE"
numericstring = *DIGIT
printablestring = *( ps-char )
ps-restricted-char = 1DIGIT / 1ALPHA / " " / "'" / "+"
/ "," / "-" / "." / "/" / ":" / "=" / "?"
ps-delim = "(" / ")"
ps-char = ps-delim / ps-restricted-char
ps-encoded = *( ps-restricted-char / ps-encoded-char )
ps-encoded-char = "(a)" ; (@)
/ "(p)" ; (%)
/ "(b)" ; (!)
/ "(q)" ; (")
/ "(u)" ; (_)
/ "(l)" ; "("
/ "(r)" ; ")"
/ "(" 3DIGIT ")"
teletex-string = *( ps-char / t61-encoded )
t61-encoded = "{" 1* t61-encoded-char "}"
t61-encoded-char = 3DIGIT
teletex-and-or-ps = [ printablestring ] [ "*" teletex-string ]
labelled-integer ::= [ key-string ] "(" numericstring ")"
key-string = *key-char
key-char = <a-z, A-Z, 0-9, and "-">
object-identifier ::= oid-comp object-identifier
| oid-comp
oid-comp ::= [ key-string ] "(" numericstring ")"
encoded-info = 1#encoded-type
encoded-type = built-in-eit / object-identifier
built-in-eit = "Undefined" ; undefined (0)
/ "Telex" ; tLX (1)
/ "IA5-Text" ; iA5Text (2)
/ "G3-Fax" ; g3Fax (3)
/ "TIF0" ; tIF0 (4)
/ "Teletex" ; tTX (5)
/ "Videotex" ; videotex (6)
/ "Voice" ; voice (7)
/ "SFD" ; sFD (8)
/ "TIF1" ; tIF1 (9)
okay so the grammar bit is where all the rules get locked in, and honestly it's giving architect energy 🧚💅 each block is copied exactly so nothing gets lost, fr fr
encoded-pn = [ given "." ] *( initial "." ) surname
given = 2*<ps-char not including ".">
initial = ALPHA
surname = printablestring
std-or-address = 1*( "/" attribute "=" value ) "/" attribute = standard-type / "RFC-822" / registered-dd-type / dd-key "." std-printablestring standard-type = key-string
registered-dd-type = key-string dd-key = key-string
value = std-printablestring
std-printablestring = ( std-char / std-pair ) std-char = <"{", "}", "", and any ps-char except "/" and "="> std-pair = "$" ps-char
dmn-or-address = dmn-part ( "." dmn-part ) dmn-part = attribute "$" value attribute = standard-type / "~" dmn-printablestring value = dmn-printablestring / "@" dmn-printablestring = = *( dmn-char / dmn-pair ) dmn-char = <"{", "}", "", and any ps-char except "."> dmn-pair = "."
global-id = std-or-address
<pink>the `std-or-address` and `dmn-or-address` rules are the main character of this section 💖</pink> next up is the MTA trace stuff and the delivery report bits 🦋
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-or-mta ";" ] action-list ";" arrival-time
md-and-mta = [ "mta" mta "in" ] global-id mta = word arrival-time = date-time md-or-mta = "MD" global-id / "MTA" mta
Action-list = 1#action action = "Redirected" / "Expanded" / "Relayed" / "Rerouted"
dr-body-format = dr-summary <CRLF> dr-recipients <CRLF> dr-administrator-info-envelope <CRLF> dr-content-return
dr-content-return = "The Original Message is not available" / "The Original Message follows:"
dr-summary = "This report relates to your message:" <CRLF> content-correlator <CRLF> <CRLF> "of" 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-administrator-info-envelope = 3*( "*" text <CRLF> )
dr-administrator-info = " The following information is directed towards" "the local administrator" <CRLF> " and is not intended for the end user" <CRLF> <CRLF> "DR generated by:" report-point <CRLF> "at" date-time <CRLF> <CRLF> "Converted to RFC 822 at" mta <CRLF> "at" date-time <CRLF> <CRLF> "Delivery Report Contents:" <CRLF> <CRLF> drc-field-list <CRLF> "* End of administration information"
drc-field-list = *(drc-field <CRLF>)
drc-field = "Subject-Submision-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
<lavender>the recipient-info rules are where it gets really detailed, so hold onto your hat 🎀</lavender>
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 ")") 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 ";" / "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"
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
discard-reason = "Expired" / "Obsoleted" / "User Subscription Terminated"
acknowledgement-mode = "Manually" / "Automatically"
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"
redirect-comment = [ "Originally To:" ] mailbox "Redirected" [ "Again" ] "on" date-time "To:" redirection-reason
redirection-reason = "Recipient Assigned Alternate Recipient" / "Originator Requested Alternate Recipient" / "Recipient MD Assigned Alternate Recipient"
subject-line = "Delivery-Report" "(" status ")" [ "for" destination ]
status = "success" / "failure" / "success and failures"
destination = mailbox / "MTA" word
extended-heading = "Prevent-NonDelivery-Report" ":" / "Generate-Delivery-Report" ":" / "Alternate-Recipient" ":" prohibition / "Disclose-Recipients" ":" prohibition / "Content-Return" ":" prohibition
# Appendix F - Format of address mapping tables 🗂️✨
Okay bestie, this appendix is where the mapping tables live, and they're giving organised 💅. Let's go.
## 1. Global Mapping Information 🌍
Gateways that follow this spec need three globally defined mappings to stay consistent. The whole thing depends on them 🫶:
1. Domain Name Space -> O/R Address Space
2. O/R Address Space -> Domain Name Space
3. Domain Name Space -> O/R Address of preferred gateway
All gateways conforming to this specification SHALL have access to these mappings. The gateway MAY use standardised or private mechanisms to access this mapping information. Lowkey flexible 🦋
One way to distribute this info is in three files, and this appendix defines a format for those files. Other standardised mechanisms to distribute the mapping information are expected. Mechanisms for using the Domain Name Scheme and X.500 are planned, specifically 🧚
The COSINE-MHS project is coordinating the definition of global mapping information, on behalf of the Internet and other X.400 and RFC 822 users. If you want info on accessing it, contact:
COSINE MHS Project Team SWITCH Weinbergstrasse 18 8001 Zuerich Switzerland
tel: +41 1 262 3143 fax: +41 1 262 3151 email: C=ch;ADMD=arcom;PRMD=switch;O=switch;OU=cosine-mhs; S=project-team or project-team@cosine-mhs.switch.ch
## 2. Syntax Definitions 🧩
So there's an address syntax that's compatible with the syntax used for 822.domains. Representing O/R addresses as domains means every lookup can be done mechanically as a domain -> domain mapping. It's initially for table format, but it's built so it can be adapted for the Domain Name Service too. It allows a general representation of O/R addresses, so other applications can use it. Not every attribute is used in the table formats, which is totally fine 💖
To represent null attributes, the pseudo-value `"@"` (not a printable string character) shows that a level in the hierarchy is omitted. This is different from including the element with no value, although a correct X.400 implementation will interpret both the same way 🙈
This syntax is not intended to be handled by users.
dmn-or-address = dmn-part ( "." dmn-part ) dmn-part = attribute "$" value attribute = standard-type / "~" dmn-printablestring value = dmn-printablestring / "@" dmn-printablestring = = *( dmn-char / dmn-pair ) dmn-char = <"{", "}", "", and any ps-char except "."> dmn-pair = "."
An example usage:
~ROLE$Big.Chief.ADMD$ATT.C$US PRMD$DEC.ADMD$@.C$US
The first example shows a `"."` being quoted, and the second leaves out the ADMD level. There MUST be a strict ordering of all components in this table, with the most significant components on the RHS. That ordering is what lets the encoding be treated as a domain 🔥
Further restrictions apply to how dmn-or-address is used in the address space mapping tables:
1. Only C, ADMD, PRMD, O, and up to four OUs MAY be used.
2. No components SHALL be omitted from this hierarchy, although the hierarchy MAY terminate at any level. If the mapping is to an omitted component, the `"@"` syntax is used.
## 3. Table Lookups 🔎
Some things apply to every lookup. Matches are always case independent. The key for all three tables is a domain, and the longest possible match SHALL be obtained. Say the table has two entries with these keys:
K.L J.K.L
Domain "A.B.C" will not return any matches, bestie 💀 Domain "I.J.K.L" will match the entry `"J.K.L:.`
## 4. Domain -> O/R Address format 🎯
The BNF is:
domain-syntax "#" dmn-or-address "#"
The trailing "#" is there for clarity, since dmn-or-address might lead to values with trailing blanks. Lines starting with "#" are comments ✨
For example:
AC.UK#PRMD$UK.AC.ADMD$GOLD 400.C$GB# XEROX.COM#O$Xerox.ADMD$ATT.C$US# GMD.DE#O$@.PRMD$GMD.ADMD$DBP.C$DE#
A domain gets looked up to find the top levels of an O/R Address. Any components of the domain that don't match get used to build the rest of the O/R address, as described in Section 4.3.4 🧁
## 5. O/R Address -> Domain format 🔄
The syntax of this table is:
dmn-or-address "#" domain-syntax "#"
For example:
#
Mapping table
# PRMD$UK.AC.ADMD$GOLD 400.C$GB#AC.UK#
The O/R Address is used to generate a domain key. Ordering the components correctly matters a lot, and so does filling in the missing components in the hierarchy. This mapping is used as described in Section 4.3.2 💅
## 6. Domain -> O/R Address of Gateway table 🚪
This uses the same format as the domain -> O/R address mapping. In this case, the two restrictions (omitted components and restrictions on components) do not apply. This mapping is used as described in Section 4.3.4 🌸
---
# Appendix G - Mapping with X.400(1984) 🎀
This appendix defines changes to the mapping for use with X.400(1984), so let's get into it 🦋
The X.400(1984) protocols are a proper subset of X.400(1988). When mapping from X.400(1984) to RFC 822, no changes to this specification are needed. Easy 💖
Going the other way, from RFC 822 to X.400(1984), no 1988-specific features can be used. None of them are used at the MTS level. One feature is used at the IPMS level, and this MUST be replaced by the RFC 987 approach 😭 All header information that would usually be mapped into the `rfc-822-heading-list` extension, plus any `Comments:` field in the RFC 822 header, gets mapped into a single IA5 body part. That body part is the first body part in the message. It starts with the string `RFC-822-Headers:` as its first line, and the headers follow that line. This specification requires correct reverse mapping of this format, whether it's from 1988 or 1984 ✨
If RFC 822 is a big deal in your environment, it MAY be desirable for downgrading to consider a message that started in an RFC 822 system and got mapped according to this specification. The `rfc-822-heading-list` extension MAY be mapped according to this appendix 🫶
When parsing std-or, the following restrictions MUST be observed:
- Only the 84/88 attributes identified in the table in Section 4.2 are present.
- No teletex encoding is allowed.
If an address breaks these rules, it SHOULD be treated as an RFC 822 address, which will usually lead to encoding as a DDA `"RFC-822"` 🙈
It's possible that null attributes MAY be present in an O/R Address. That's not legal in 1988, except for ADMD, where the case is explicitly described in Section 4.3.5. Null attributes are deprecated (the attribute SHOULD be omitted), and they SHOULD therefore be unusual. Still, some systems generate them and rely on them, so any null attribute SHALL be encoded using the std-or encoding (e.g., `/O=/`) 🧚
If a non-Teletex Common Name (CN) is present, it SHOULD be mapped onto a Domain Defined Attribute "Common". This lines up with RFC 1328 on X.400 1988 to 1984 downgrading [Hardcastle-K92] 💜
---
# Appendix H - RFC 822 Extensions for X.400 access 🦋
This appendix defines a bunch of OPTIONAL mappings that MAY be provided to give access from RFC 822 to some X.400 services. They're beyond the basic scope of this specification, but people really wanted to use extended RFC 822 to access X.400, so these extensions give access to certain features. If this functionality is provided, this appendix SHALL be followed. The following headings are defined:
extended-heading = "Prevent-NonDelivery-Report" ":" / "Generate-Delivery-Report" ":" / "Alternate-Recipient" ":" prohibition / "Disclose-Recipients" ":" prohibition / "Content-Return" ":" prohibition
`Prevent-NonDelivery-Report` and `Generate-Delivery-Report` allow setting of MTS.PerRecipientSubmissionFields.originator-report-request. The setting is the same for all recipients 🍓
`Alternate-Recipient`, `Disclose-Recipients`, and `Content-Return` allow overriding the default settings for MTS.PerMessageIndicators 👑
---
# Appendix I - Conformance 🏆
This appendix defines a number of options that a conforming gateway SHOULD specify. Conformance to this specification SHALL NOT be claimed if any of the mandatory features are not implemented. In particular:
- Formats for all fields SHALL be followed.
- Formats for subject lines, delivery reports and IPNs SHALL be followed. A system that followed the syntax but translated text into a language other than English would still be conformant 🌈
- RFC 1137 SHALL NOT be followed when mapping to SMTP or to JNT Mail
- All mappings of trace SHALL be implemented.
- There MUST be a mechanism to access all three global mappings.
A gateway SHOULD specify:
- Which 822-MTS protocols are supported. The relevant appendices MUST be followed to claim support for a given protocol: SMTP (A); JNT Mail (B); UUCP (C).
- Which X.400 versions are supported (84 and/or 88).
- The means by which it can access the global mappings. Currently, the tables of the formats defined in Appendix F are the only means available.
- The approach taken when upper bounds are exceeded at the IPM level (5.1.3)
- The approach taken to return of contents (5.2)
- The approach taken to body parts which cannot be converted (5.3.4)
- The approach taken to multiple copies vs non-disclosure (4.6.2.2)
The following are OPTIONAL parts of this specification. A conforming implementation SHOULD specify which of these it supports 🥹
- Generation of extended RFC 822 fields is mandatory. Optionally, they MAY be parsed and mapped back to X.400. A gateway SHOULD SHOULD indicate if this is done (yes, that's two SHOULDs, the original really said it twice 💀)
- Support for the extension mappings of Appendix H.
- Support for returning illegal format content in a delivery report
- Which address interpretation heuristics are supported (4.3.4.1)
- If RFC 987 generated message ids are handled in a backwards compatible manner (4.7.3.6)
# Appendix J - Change History: RFC 987, 1026, 1138, 1148 🕰️
okay so <pink>RFC 987</pink> was the original doc 🫶 It had the key elements of this whole spec and it was specific to X.400(1984). Then <lavender>RFC 1026</lavender> came in and made a small number of necessary changes to it. ✨
RFC 1138 was based on the RFC 987 work, but it had an editorial error, so it got reissued a few months later as RFC 1148. We'll be talking about RFC 1148 here because it's the one everyone cites elsewhere 📚 Its major goal was to upgrade RFC 987 to X.400(1988). It did that ✅ but it did **not** obsolete RFC 987, which was still recommended for use with X.400(1984). This appendix is the tea on what changed going from RFC 987 to RFC 1148 ☕
RFC 1148 said this about its own upgrade (iconic, honestly):
> "Unnecessary change is usually a bad idea." 🙈
Changes on the RFC 822 side were avoided as far as possible, so RFC 822 users don't see random differences between systems that follow this spec and systems that follow RFC 987. Changes on the X.400 side were minimised, but they're more acceptable because the mapping now lands on a new set of services and protocols. Main character energy for the X.400 side 💅
## 1. Introduction 🧚
- The model went from a protocol based mapping to a service based mapping. This made the spec more general and improved the model overall, and it affects the entire document. 🌈
- A restriction on scope was added.
## 2. Service Elements 🎀
- The new service elements of X.400 are dealt with.
- A clear distinction is now made between origination and reception.
## 3. Basic Mappings 🍓
- Teletex support was added.
- Object identifier support was added.
- Labelled integer support was added.
- The `PrintableString <-> ASCII` mapping was made reversible.
- The printable string mapping was aligned to the NBS mapping derived from RFC 987.
## 4. Addressing 🌸
- Support for new addressing attributes was added.
- The message ID mapping was changed so it is not table driven anymore.
## 5. Detailed Mappings 💜
- An extended IPM Header was defined, and it's used instead of a second body part for RFC 822 extensions.
- Element names were realigned.
- There's a new syntax for reports. It simplifies the header and introduces a mandatory body format, because the RFC 987 header format was unusable 😭
- The complex autoforwarded mapping was dropped.
- A full mapping for IP Notifications was added, and it defines a body format.
- An MTS Identifier syntax was adopted, lining it up with the O/R Address syntax.
- A new format for the X400 Trace representation was added on the RFC 822 side.
## 6. Appendices 🦋
- The Appendix on restricted 822 mappings was moved to a separate RFC.
- The Phonenet and SMTP Appendixes were deleted.
---
# Appendix K - Change History: RFC 1148 to this Document 🧁
## 1. General 👑
- The scope was changed to cover X.400(1984), which means this one obsoletes RFC 987.
- Changes were made so people can use RFC 822 networks connected through X.400.
- The text was tightened to make it clear which aspects are optional and which are mandatory. Very clean. 💅
- There was a good deal of clarification.
- A number of minor EBNF errors were fixed. 🙈
- Better examples were added.
- Further X.400 upper bounds are now handled correctly.
## 2. Basic Mappings 🍓
- The encoding of object identifier was changed slightly.
## 3. Addressing 🌈
- A global mapping of domain to preferred gateway was introduced.
- An overflow mechanism was defined for RFC 822 addresses longer than 128 bytes.
- Changes were made to improve compatibility with the PDAM when writing O/R Addresses:
- The `PD` and `Terminal Type` keywords were aligned to the PDAM. It is believed that minimal use has been made of the RFC 1148 keywords.
- `P` and `A` are allowed as alternate keys for `PRMD` and `ADMD`.
- Where keywords are different, the PDAM keywords are alternatives on input. This is mandatory.
## 4. Detailed Mappings 🔥
- The format of the `Subject:` lines is defined.
- Illegal use (repetition) of the heading `EXTENSION` was corrected, and a new object identifier was assigned.
- The Delivery Report format was extensively revised in light of operational experience.
- The handling of redirects was significantly changed, because the previous mechanism did not work. 💀
## 5. Appendices ✨
- An SMTP appendix was added, allowing optional use of the VRFY command to improve probe information.
- The handling of JNT Mail Acknowledge-To was changed slightly.
- A `DDA JNT-MAIL` is allowed on input.
- The format definitions of Appendix F are explained further, and a third table definition was added.
- An appendix on use with X.400(1984) was added.
- Optional extensions were defined to give RFC 822 access to further X.400 facilities.
- An appendix on conformance was added.
---
# References 📚
**CCITT88a.** CCITT, "CCITT Recommendations X.408," Message Handling Systems: Encoded Information Type Conversion Rules, December 1988.
**CCITT/ISO88a.** CCITT/ISO, "CCITT Recommendations X.400/ ISO IS 10021-1," Message Handling: System and Service Overview , December 1988.
**CCITT/ISO88b.** CCITT/ISO, "CCITT Recommendations X.420/ ISO IS 10021-7," Message Handling Systems: Interpersonal Messaging System, 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, December 1988.
**CCITT/ISO88d.** CCITT/ISO, "Specification of Abstract Syntax Notation One (ASN.1)," CCITT Recommendation X.208 / ISO IS 8824, December 1988.
**CCITT/ISO91a.** CCITT/ISO, "Representation of O/R Addresses for Human Usage," PDAM to CCITT X.401 / ISO/IEC 10021-2, February 1991.
**Crocker82a.** Crocker, D., "Standard of the Format of ARPA Internet Text Messages," RFC 822, UDEL, August 1982.
**Hardcastle-K92.** Hardcastle-Kille, S., "X.400 1988 to 1984 downgrading," RFC 1328, UCL, May 1992.
**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, October 1989.
**Kille90a.** Kille, S., "Mapping Between X.400(1988) / ISO 10021 and RFC 822," RFC 1148, March 1990.
**Larmouth83a.** Larmouth, J., "JNT Name Registration Technical Guide," Salford University Computer Centre, April 1983.
**Postel84a.** Postel J., and J. Reynolds, "Domain Requirements," RFC 920, USC/Information Sciences Institute, October 1984.
**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. 💀 Plot twist, but it's the honest answer: this memo leaves security issues out entirely, so there is nothing more to add here.
---
# AUTHOR'S ADDRESS 🎀
Steve Hardcastle-Kille Department of Computer Science University College London Gower Street WC1E 6BT England
Phone: +44-71-380-7294 EMail: S.Kille@CS.UCL.AC.UK
📦 where this page comes from
- ietf: rfc1327 1992-05
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms