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1327 Mapping between X. May 1992 Status: PROPOSED STANDARD 1327 Mapping between X.400(1988) / ISO 10021 and RFC 822. S.Hardcastle-Kille. May 1992. (Format: TXT=228598 bytes) (ObsoletesRFC0987, RFC1026, RFC1138, RFC1148) (Obsoleted by RFC1495, RFC2156)(Updates RFC0822) (Status: PROPOSED STANDARD)
Network Working Group S. Hardcastle-Kille
Request for Comments: 1327 University College London
Obsoletes: RFCs 987, 1026, 1138, 1148 May 1992
Updates: RFC 822
Mapping between X.400(1988) / ISO 10021 and RFC 822
Status of this Memo
This RFC specifies an IAB standards track protocol for the Internet
community, and requests discussion and suggestions for improvements.
Please refer to the current edition of the "IAB Official Protocol
Standards" for the standardization state and status of this protocol.
Distribution of this memo is unlimited.
Abstract
This document describes a set of mappings which will enable
interworking between systems operating the CCITT X.400 1988)
Recommendations on Message Handling Systems / ISO IEC 10021 Message
Oriented Text Interchange Systems (MOTIS) [CCITT/ISO88a], and systems
using the RFC 822 mail protocol [Crocker82a] or protocols derived
from RFC 822. The approach aims to maximise the services offered
across the boundary, whilst not requiring unduly complex mappings.
The mappings should not require any changes to end systems. This
document is 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. This specification
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
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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
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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 ........................................... 113
Chapter 1 -- Overview
1.1. X.400
This document relates to the CCITT 1988 X.400 Series Recommendations
/ ISO IEC 10021 on the Message Oriented Text Interchange Service
(MOTIS). This ISO/CCITT standard is referred to in this document as
"X.400", which is a convenient shorthand. Any reference to the 1984
CCITT Recommendations will be explicit. X.400 defines an
Interpersonal Messaging System (IPMS), making use of a store and
forward Message Transfer System. This document relates to the IPMS,
and not to wider application of X.400. It is expected that X.400
will be implemented very widely.
1.2. RFC 822
RFC 822 evolved as a messaging standard on the DARPA (the US Defense
Advanced Research Projects Agency) Internet. It specifies and end to
end message format. It is used in conjunction with a number of
different message transfer protocol environments.
SMTP Networks
On the DARPA Internet and other TCP/IP networks, RFC 822 is
used in conjunction with two other standards: RFC 821, also
known as Simple Mail Transfer Protocol (SMTP) [Postel82a],
and RFC 920 which is a Specification for domains and a
distributed name service [Postel84a].
UUCP Networks
UUCP is the UNIX to UNIX CoPy protocol, which is usually
used over dialup telephone networks to provide a simple
message transfer mechanism. There are some extensions to
RFC 822, particularly in the addressing. They use domains
which conform to RFC 920, but not the corresponding domain
nameservers [Horton86a].
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Bitnet
Some parts of Bitnet and related networks use RFC 822
related protocols, with EBCDIC encoding.
JNT Mail Networks
A number of X.25 networks, particularly those associated
with the UK Academic Community, use the JNT (Joint Network
Team) Mail Protocol, also known as Greybook [Kille84a].
This is used with domains and name service specified by the
JNT NRS (Name Registration Scheme) [Larmouth83a].
The mappings specified here are appropriate for all of these
networks.
1.3. The need for conversion
There is a large community using RFC 822 based protocols for mail
services, who will wish to communicate with users of the IPMS
provided by X.400 systems. This will also be a requirement in cases
where communities intend to make a transition to use of an X.400
IPMS, as conversion will be needed to ensure a smooth service
transition. It is expected that there will be more than one gateway,
and this specification will enable them to behave in a consistent
manner. Note that the term gateway is used to describe a component
performing the protocol mappings between RFC 822 and X.400. This is
standard usage amongst mail implementors, but should be noted
carefully by transport and network service implementors.
Consistency between gateways is desirable to provide:
1. Consistent service to users.
2. The best service in cases where a message passes through
multiple gateways.
1.4. General approach
There are a number of basic principles underlying the details of the
specification. These principles are goals, and are not achieved in
all aspects of the specification.
1. The specification should be pragmatic. There should not be
a requirement for complex mappings for "Academic" reasons.
Complex mappings should not be required to support trivial
additional functionality.
2. Subject to 1), functionality across a gateway should be as
high as possible.
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3. It is always a bad idea to lose information as a result of
any transformation. Hence, it is a bad idea for a gateway
to discard information in the objects it processes. This
includes requested services which cannot be fully mapped.
4. All mail gateways actually operate at exactly one level
above the layer on which they conceptually operate. This
implies that the gateway must not only be cognisant of the
semantics of objects at the gateway level, but also be
cognisant of higher level semantics. If meaningful
transformation of the objects that the gateway operates on
is to occur, then the gateway needs to understand more than
the objects themselves.
5. 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
X.400 defines the IPMS Abstract Service in X.420/ISO 10021-7,
[CCITT/ISO88b] which comprises of three basic services:
1. Origination
2. Reception
3. Management
Management is a local interaction between the user and the IPMS, and
is therefore not relevant to gatewaying. The first two services
consist of operations to originate and receive the following two
objects:
1. IPM (Interpersonal Message). This has two components: a
heading, and a body. The body is structured as a sequence
of body parts, which may be basic components (e.g., IA5
text, or G3 fax), or IP Messages. The heading consists of
fields containing end to end user information, such as
subject, primary recipients (To:), and importance.
2. IPN (Inter Personal Notification). A notification about
receipt of a given IPM at the UA level.
The Origination service also allows for origination of a probe, which
is an object to test whether a given IPM could be correctly received.
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The Reception service also allows for receipt of Delivery Reports
DR), which indicate delivery success or failure.
These IPMS Services utilise the Message Transfer (MT) Abstract
Service [CCITT/ISO88c]. The MT Abstract Service provides the
following three basic services:
1. Submission (used by IPMS Origination)
2. Delivery (used by IPMS Reception)
3. Administration (used by IPMS Management)
Administration is a local issue, and so does not affect this
standard. Submission and delivery relate primarily to the MTS
Message (comprising Envelope and Content), which carries an IPM or
IPN (or other uninterpreted contents). There is also an Envelope,
which includes an ID, an originator, and a list of recipients.
Submission also includes the probe service, which supports the IPMS
Probe. Delivery also includes Reports, which indicate whether a given
MTS Message has been delivered or not.
The MTS is REFINED into the MTA (Message Transfer Agent) Service,
which defines the interaction between MTAs, along with the procedures
for distributed operation. This service provides for transfer of MTS
Messages, Probes, and Reports.
1.5.2. RFC 822
RFC 822 is based on the assumption that there is an underlying
service, which is here called the 822-MTS service. The 822-MTS
service provides three basic functions:
1. Identification of a list of recipients.
2. Identification of an error return address.
3. Transfer of an RFC 822 message.
It is possible to achieve 2) within the RFC 822 header. Some 822-MTS
protocols, in particular SMTP, can provide additional functionality,
but as these are neither mandatory in SMTP, nor available in other
822-MTS protocols, they are not considered here. Details of aspects
specific to two 822-MTS protocols are given in Appendices B and C.
An RFC 822 message consists of a header, and content which is
uninterpreted ASCII text. The header is divided into fields, which
are the protocol elements. Most of these fields are analogous to P2
heading fields, although some are analogous to MTS Service Elements
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or MTA Service Elements.
1.5.3. The Gateway
Given this functional description of the two services, the functional
nature of a gateway can now be considered. It would be elegant to
consider the 822-MTS service mapping onto the MTS Service Elements
and RFC 822 mapping onto an IPM, but reality just does not fit.
Another elegant approach would be to treat this document as the
definition of an X.400 Access Unit (AU). Again, reality does not
fit. It is necessary to consider that the IPM format definition, the
IPMS Service Elements, the MTS Service Elements, and MTA Service
Elements on one side are mapped into RFC 822 + 822-MTS on the other
in a slightly tangled manner. The details of the tangle will be made
clear in Chapter 5. Access to the MTA Service Elements is minimised.
The following basic mappings are thus defined. When going from RFC
822 to X.400, an RFC 822 message and the associated 822-MTS
information is always mapped into an IPM (MTA, MTS, and IPMS
Services). Going from X.400 to RFC 822, an RFC 822 message and the
associated 822-MTS information may be derived from:
1. A Report (MTA, and MTS Services)
2. An IPN (MTA, MTS, and IPMS services)
3. An IPM (MTA, MTS, and IPMS services)
Probes (MTA Service) must be processed by the gateway, as discussed
in Chapter 5. MTS Messages containing Content Types other than those
defined by the IPMS are not mapped by the gateway, and should be
rejected at the gateway.
1.5.4. Repeated Mappings
The 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.
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Where an X.400 messages 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 in 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 that 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
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 is to make clear some
limitations of scope. In particular, this specification does not
specify:
- Extensions of RFC 822 to provide access to all X.400
services
- X.400 user interface definition
- 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
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all X.400 services. Thus, it will be a poor choice for X.400
implementors to use RFC 987(88) as an interface - there are too many
aspects of X.400 which cannot be accessed through it. If a text
interface is desired, a 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:
1. Overview - this chapter.
2. Service Elements - This describes the (end user) services
mapped by a gateway.
3. Basic mappings - This describes some basic notation used in
Chapters 3-5, the mappings between character sets, and some
fundamental protocol elements.
4. Addressing - This considers the mapping between X.400 O/R
names and RFC 822 addresses, which is a fundamental gateway
component.
5. Detailed Mappings - This describes the details of all other
mappings.
There are also 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.
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A number of comments from people on RFC 1148 lead 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
When a user originates a message, a number of services are available.
Some of these imply actions (e.g., delivery to a recipient), and some
are insertion of known data (e.g., specification of a subject field).
This chapter describes, for each offered service, to what extent it
is supported for a recipient accessed through a gateway. There are
three levels of support:
Supported
The corresponding protocol elements map well, and so the
service can be fully provided.
Not Supported
The service cannot be provided, as there is a complete
mismatch.
Partial Support
The service can be partially fulfilled.
In the first two cases, the service is simply marked as Supported" or
"Not Supported". Some explanation may be given if there are
additional implications, or the (non) support is not intuitive. For
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partial support, the level of partial support is summarised. Where
partial support is good, this will be described by a phrase such as
"Supported by use of.....". A common case of this is where the
service is mapped onto a non- standard service on the other side of
the gateway, and this would have lead to support if it had been a
standard service. In many cases, this is equivalent to support. For
partial support, an indication of the mechanism is given, in order to
give a feel for the level of support provided. Note that this is not
a replacement for Chapter 5, where the mapping is fully specified.
If a service is described as supported, this implies:
- Semantic correspondence.
- No (significant) loss of information.
- Any actions required by the service element.
An example of a service gaining full support: If an RFC 822
originator specifies a Subject: field, this is considered to be
supported, as an X.400 recipient will get a subject indication.
In many cases, the required action will simply be to make the
information available to the end user. In other cases, actions may
imply generating a delivery report.
All RFC 822 services are supported or partially supported for
origination. The implications of non-supported X.400 services is
described under X.400.
2.1.2. Reception of Messages
For reception, the list of service elements required to support this
mapping is specified. This is really an indication of what a
recipient might expect to see in a message which has been remotely
originated.
2.2. RFC 822
RFC 822 does not explicitly define service elements, as distinct from
protocol elements. However, all of the RFC 822 header fields, with
the exception of trace, can be regarded as corresponding to implicit
RFC 822 service elements.
2.2.1. Origination in RFC 822
A mechanism of mapping, used in several cases, is to map the RFC 822
header into a heading extension in the IPM (InterPersonal Message).
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This can be regarded as partial support, as it makes the information
available to any X.400 implementations which are interested in these
services. Communities which require significant RFC 822 interworking
are recommended to require that their X.400 User Agents are able to
display these heading extensions. Support for the various service
elements (headers) is now listed.
Date:
Supported.
From:
Supported. For messages where there is also a sender field,
the mapping is to "Authorising Users Indication", which has
subtly different semantics to the general RFC 822 usage of
From:.
Sender:
Supported.
Reply-To:
Supported.
To: Supported.
Cc: Supported.
Bcc: Supported.
Message-Id:
Supported.
In-Reply-To:
Supported, for a single reference. Where multiple
references are given, partial support is given by mapping to
"Cross Referencing Indication". This gives similar
semantics.
References:
Supported.
Keywords:
Supported by use of a heading extension.
Subject:
Supported.
Comments:
Supported by use of an extra body part.
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Encrypted:
Supported by use of a heading extension.
Resent-*
Supported by use of a heading extension. Note that
addresses in these fields are mapped onto text, and so are
not accessible to the X.400 user as addresses. In
principle, fuller support would be possible by mapping onto
a forwarded IP Message, but this is not suggested.
Other Fields
In particular X-* fields, and "illegal" fields in common
usage (e.g., "Fruit-of-the-day:") are supported by use of
heading extensions.
2.2.2. Reception by RFC 822
This considers reception by an RFC 822 User Agent of a message
originated in an X.400 system and transferred across a gateway. The
following standard services (headers) may be present in such a
message:
Date:
From:
Sender:
Reply-To:
To:
Cc:
Bcc:
Message-Id:
In-Reply-To:
References:
Subject:
The following non-standard services (headers) may be present. These
are defined in more detail in Chapter 5 (5.3.4, 5.3.6, 5.3.7):
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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:
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X400-Originator:
X400-Received:
X400-Recipients:
2.3. X.400
2.3.1. Origination in X.400
When mapping services from X.400 to RFC 822 which are not supported
by RFC 822, new RFC 822 headers are defined. It is intended that
these fields will be registered, and that co- operating RFC 822
systems may use them. Where these new fields are used, and no system
action is implied, the service can be regarded as being partially
supported. Chapter 5 describes how to map X.400 services onto these
new headers. Other elements are provided, in part, by the gateway as
they cannot be provided by RFC 822.
Some service elements are marked N/A (not applicable). There are
five cases, which are marked with different comments:
N/A (local)
These elements are only applicable to User Agent / Message
Transfer Agent interaction and so they cannot apply to RFC
822 recipients.
N/A (PDAU)
These service elements are only applicable where the
recipient is reached by use of a Physical Delivery Access
Unit (PDAU), and so do not need to be mapped by the gateway.
N/A (reception)
These services are only applicable for reception.
N/A (prior)
If requested, this service must be performed prior to the
gateway.
N/A (MS)
These services are only applicable to Message Store (i.e., a
local service).
Finally, some service elements are not supported. In particular, the
new security services are not mapped onto RFC 822. Unless otherwise
indicated, the behaviour of service elements marked as not supported
will depend on the criticality marking supplied by the user. If the
element is marked as critical for transfer or delivery, a non-
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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
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will only be done where content conversion is not
prohibited.
User Capabilities Registration
N/A (local).
2.3.1.2. IPM Service Optional User Facilities
This section describes support for the optional (user selectable) IPM
services as listed in Section 19.9 of X.400 / ISO/IEC 10021- 1,
listed here in the order given. Section 19.9 has cross references to
short definitions of each service.
Additional Physical Rendition
N/A (PDAU).
Alternate Recipient Allowed
Not supported. There is no RFC 822 service equivalent to
prohibition of alternate recipient assignment (e.g., an RFC
822 system may freely send an undeliverable message to a
local postmaster). Thus, the gateway cannot prevent
assignment of alternative recipients on the RFC 822 side.
This service really means giving the user control as to
whether or not an alternate recipient is allowed. This
specification requires transfer of messages to RFC 822
irrespective of this service request, and so this service is
not supported.
Authorising User's Indication
Supported.
Auto-forwarded Indication
Supported as new RFC 822 header (Auto-Forwarded:).
Basic Physical Rendition
N/A (PDAU).
Blind Copy Recipient Indication
Supported.
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.
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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 descriptive information for the RFC 822 recipient,
and is not reverse mappable.
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DL Expansion History Indication
Supported by use of a new RFC 822 header
DL-Expansion-History:).
DL Expansion Prohibited
Distribution List means MTS supported distribution list, in
the manner of X.400. This service does not exist in the RFC
822 world. RFC 822 distribution lists should be regarded as
an informal redistribution mechanism, beyond the scope of
this control. Messages will be sent to RFC 822,
irrespective of whether this service is requested.
Theoretically therefore, this service is supported, although
in practice it may appear that it is not supported.
Express Mail Service
N/A (PDAU).
Expiry Date Indication
Supported as new RFC 822 header (Expiry-Date:). In general,
no automatic action can be expected.
Explicit Conversion
N/A (prior).
Forwarded IP Message Indication
Supported, with some loss of information. The message is
forwarded in an RFC 822 body, and so can only be interpreted
visually.
Grade of Delivery Selection
N/A (PDAU)
Importance Indication
Supported as new RFC 822 header (Importance:).
Incomplete Copy Indication
Supported as new RFC 822 header (Incomplete-Copy:).
Language Indication
Supported as new RFC 822 header (Language:).
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.
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Message Origin Authentication
N/A (reception).
Message Security Labelling
Not supported.
Message Sequence Integrity
Not supported.
Multi-Destination Delivery
Supported.
Multi-part Body
Supported, with some loss of information, in that the
structuring cannot be formalised in RFC 822.
Non Receipt Notification Request
Not supported.
Non Repudiation of Delivery
Not supported.
Non Repudiation of Origin
N/A (reception).
Non Repudiation of Submission
N/A (local).
Obsoleting Indication
Supported as new RFC 822 header (Obsoletes:).
Ordinary Mail
N/A (PDAU).
Originator Indication
Supported.
Originator Requested Alternate Recipient
Not supported, but is placed as comment next to address
X400-Recipients:).
Physical Delivery Notification by MHS
N/A (PDAU).
Physical Delivery Notification by PDS
N/A (PDAU).
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Physical Forwarding Allowed
Supported by use of a comment in a new RFC 822 header
X400-Recipients:), associated with the recipient in
question.
Physical Forwarding Prohibited
Supported by use of a comment in a new RFC 822 header
X400-Recipients:), associated with the recipient in
question.
Prevention of Non-delivery notification
Supported, as delivery notifications cannot be generated by
RFC 822. In practice, errors will be returned as IP
Messages, and so this service may appear not to be supported
see Non-delivery Notification).
Primary and Copy Recipients Indication
Supported
Probe
Supported at the gateway (i.e., the gateway services the
probe).
Probe Origin Authentication
N/A (reception).
Proof of Delivery
Not supported.
Proof of Submission
N/A (local).
Receipt Notification Request Indication
Not supported.
Redirection Allowed by Originator
Redirection means MTS supported redirection, in the manner
of X.400. This service does not exist in the RFC 822 world.
RFC 822 redirection (e.g., aliasing) should be regarded as
an informal redirection mechanism, beyond the scope of this
control. Messages will be sent to RFC 822, irrespective of
whether this service is requested. Theoretically therefore,
this service is supported, although in practice it may
appear that it is not supported.
Registered Mail
N/A (PDAU).
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RFC 1327 Mapping between X.400(1988) and RFC 822 May 1992
Registered Mail to Addressee in Person
N/A (PDAU).
Reply Request Indication
Supported as comment next to address.
Replying IP Message Indication
Supported.
Report Origin Authentication
N/A (reception).
Request for Forwarding Address
N/A (PDAU).
Requested Delivery Method
N/A (local). The services required must be dealt with at
submission time. Any such request is made available through
the gateway by use of a comment associated with the
recipient in question.
Return of Content
In principle, this is N/A, as non-delivery notifications are
not supported. In practice, most RFC 822 systems will
return part or all of the content along with the IP Message
indicating an error (see Non-delivery Notification).
Sensitivity Indication
Supported as new RFC 822 header (Sensitivity:).
Special Delivery
N/A (PDAU).
Stored Message Deletion
N/A (MS).
Stored Message Fetching
N/A (MS).
Stored Message Listing
N/A (MS).
Stored Message Summary
N/A (MS).
Subject Indication
Supported.
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Undeliverable Mail with Return of Physical Message
N/A (PDAU).
Use of Distribution List
In principle this applies only to X.400 supported
distribution lists (see DL Expansion Prohibited).
Theoretically, this service is N/A (prior). In practice,
because of informal RFC 822 lists, this service can be
regarded as supported.
2.3.2. Reception by X.400
2.3.2.1. Standard Mandatory Services
The following standard IPM mandatory user facilities are required
for reception of RFC 822 originated mail by an X.400 UA.
Content Type Indication
Delivery Time Stamp Indication
IP Message Identification
Message Identification
Non-delivery Notification
Original Encoded Information Types Indication
Submission Time Stamp Indication
Typed Body
2.3.2.2. Standard Optional Services
The following standard IPM optional user facilities are required for
reception of RFC 822 originated mail by an X.400 UA.
Authorising User's Indication
Blind Copy Recipient Indication
Cross Referencing Indication
Originator Indication
Primary and Copy Recipients Indication
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Replying IP Message Indication
Subject Indication
2.3.2.3. New Services
A new service "RFC 822 Header Field" is defined using the extension
facilities. This allows for any RFC 822 header field to be
represented. It may be present in RFC 822 originated messages, which
are received by an X.400 UA.
Chapter 3 Basic Mappings
3.1. Notation
The X.400 protocols are encoded in a structured manner according to
ASN.1, whereas RFC 822 is text encoded. To define a detailed
mapping, it is necessary to refer to detailed protocol elements in
each format. A notation to achieve this is described in this
section.
3.1.1. RFC 822
Structured text is defined according to the Extended Backus Naur Form
(EBNF) defined in Section 2 of RFC 822 [Crocker82a]. In the EBNF
definitions used in this specification, the syntax rules given in
Appendix D of RFC 822 are assumed. When these EBNF tokens are
referred to outside an EBNF definition, they are identified by the
string "822." appended to the beginning of the string (e.g.,
822.addr-spec). Additional syntax rules, to be used throughout this
specification, are defined in this chapter.
The EBNF is used in two ways.
1. To describe components of RFC 822 messages (or of 822-MTS
components). In this case, the lexical analysis defined in
Section 3 of RFC 822 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).
2. 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.
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- Around the ":" in all headers
- EBNF.labelled-integer
- EBNF.object-identifier
- EBNF.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 IPMSInformationObjects defined in Annex E of X.420 / ISO
10021-7.
MTS MTSAbstractService defined in Section 9 of X.411 / ISO
10021-4.
MTA MTAAbstractService defined in Section 13 of X.411 / ISO
10021-4.
The first EBNF.identifier identifies a type or value key in the
context of the defined service specification. Subsequent
EBNF.identifiers identify a value label or type in the context of the
first identifier (SET or SEQUENCE). EBNF.context indicates a context
tag, and is used where there is no label or type to uniquely identify
a component. The special EBNF.identifier keyword "value" is used to
denote an element of a sequence.
For example, IPMS.Heading.subject defines the subject element of the
IPMS heading. The same syntax is also used to refer to element
values. For example,
MTS.EncodedInformationTypes.[0].g3Fax refers to a value of
MTS.EncodedInformationTypes.[0] .
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3.2. ASCII and IA5
A gateway will interpret all IA5 as ASCII. Thus, mapping between
these forms is conceptual.
3.3. Standard Types
There is a need to convert between ASCII text, and some of the types
defined in ASN.1 [CCITT/ISO88d]. For each case, an EBNF syntax
definition is given, for use in all of this specification, which
leads to a mapping between ASN.1, and an EBNF construct. All EBNF
syntax definitions of ASN.1 types are in lower case, whereas ASN.1
types are referred to with the first letter in upper case. Except as
noted, all mappings are symmetrical.
3.3.1. Boolean
Boolean is encoded as:
boolean = "TRUE" / "FALSE"
3.3.2. NumericString
NumericString is encoded as:
numericstring = *DIGIT
3.3.3. PrintableString
PrintableString is a restricted IA5String defined as:
printablestring = *( ps-char )
ps-restricted-char = 1DIGIT / 1ALPHA / " " / "'" / "+"
/ "," / "-" / "." / "/" / ":" / "=" / "?"
ps-delim = "(" / ")"
ps-char = ps-delim / ps-restricted-char
This can be used to represent real printable strings in EBNF.
3.3.4. T.61String
In cases where T.61 strings are only used for conveying human
interpreted information, the aim of a mapping is to render the
characters appropriately in the remote character set, rather than to
maximise reversibility. For these cases, the mappings to IA5 defined
in CCITT Recommendation X.408 (1988) shall be used [CCITT/ISO88a].
These will then be encoded in ASCII.
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RFC 1327 Mapping between X.400(1988) and RFC 822 May 1992
There is also a need to represent Teletex Strings in ASCII, for some
aspects of O/R Address. For these, the following encoding is used:
teletex-string = *( ps-char / t61-encoded )
t61-encoded = "{" 1* t61-encoded-char "}"
t61-encoded-char = 3DIGIT
Common characters are mapped simply. Other octets are mapped using a
quoting mechanism similar to the printable string mechanism. Each
octet is represented as 3 decimal digits.
There are a number of places where a string may have a Teletex and/or
Printable String representation. The following BNF is used to
represent this.
teletex-and-or-ps = [ printablestring ] [ "*" teletex-string ]
The natural mapping is restricted to EBNF.ps-char, in order to make
the full BNF easier to parse.
3.3.5. UTCTime
Both UTCTime and the RFC 822 822.date-time syntax contain: Year
(lowest two digits), Month, Day of Month, hour, minute, second
(optional), and Timezone. 822.date-time also contains an optional
day of the week, but this is redundant. Therefore a symmetrical
mapping can be made between these constructs.
Note:
In practice, a gateway will need to parse various illegal
variants on 822.date-time. In cases where 822.date-time
cannot be parsed, it is recommended that the derived UTCTime
is set to the value at the time of translation.
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.
3.3.6. Integer
A basic ASN.1 Integer will be mapped onto EBNF.numericstring. In
many cases ASN.1 will enumerate Integer values or use ENUMERATED. An
EBNF encoding labelled-integer is provided. When mapping from EBNF to
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RFC 1327 Mapping between X.400(1988) and RFC 822 May 1992
ASN.1, only the integer value is mapped, and the associated text is
discarded. When mapping from ASN.1 to EBNF, addition of an
appropriate text label is strongly encouraged.
labelled-integer ::= [ key-string ] "(" numericstring ")"
key-string = *key-char
key-char = <a-z, A-Z, 0-9, and "-">
3.3.7. Object Identifier
Object identifiers are represented in a form similar to that given in
ASN.1. The order is the same as for ASN.1 (big-endian). The numbers
are mandatory, and used when mapping from the ASCII to ASN.1. The
key-strings are optional. It is recommended that as many strings as
possible are generated when mapping from ASN.1 to ASCII, to
facilitate user recognition.
object-identifier ::= oid-comp object-identifier
| oid-comp
oid-comp ::= [ key-string ] "(" numericstring ")"
An example representation of an object identifier is:
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 information in RFC 822 is represented in ASCII, and needs to be
mapped into X.400 elements encoded as printable string. For this
reason, a mechanism to represent ASCII encoded as PrintableString is
needed.
A structured subset of EBNF.printablestring is now defined. This
shall be used to encode ASCII in the PrintableString character set.
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RFC 1327 Mapping between X.400(1988) and RFC 822 May 1992
ps-encoded = *( ps-restricted-char / ps-encoded-char )
ps-encoded-char = "(a)" ; (@)
/ "(p)" ; (%)
/ "(b)" ; (!)
/ "(q)" ; (")
/ "(u)" ; (_)
/ "(l)" ; "("
/ "(r)" ; ")"
/ "(" 3DIGIT ")"
The 822.3DIGIT in EBNF.ps-encoded-char must have range 0-127, and is
interpreted in decimal as the corresponding ASCII character. Special
encodings are given for: at sign (@), percent (%), exclamation
mark/bang (!), double quote ("), underscore (_), left bracket ((),
and right bracket ()). These characters, with the exception of round
brackets, are not included in PrintableString, but are common in RFC
822 addresses. The abbreviations will ease specification of RFC 822
addresses from an X.400 system. These special encodings 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 values of printable
string (containing round braces) cannot be generated from ASCII.
Therefore, this mapping must only be used in cases where the
printable strings may only be derived from ASCII (and will therefore
have a restricted domain). For example, in this specification, it is
only applied to a Domain Defined Attribute which will have been
generated by use of this specification and a value such as "(" would
not be possible.
To encode ASCII as PrintableString, the EBNF.ps-encoded syntax is
used, with all EBNF.ps-restricted-char mapped directly. All other
822.CHAR are encoded as EBNF.ps-encoded-char.
To encode PrintableString as ASCII, parse PrintableString as
EBNF.ps-encoded, and then reverse the previous mapping. If the
PrintableString cannot be parsed, then the mapping is being applied
in to an inappropriate value, and an error shall be given to the
procedure doing the mapping. In some cases, it may be preferable to
pass the printable string through unaltered.
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RFC 1327 Mapping between X.400(1988) and RFC 822 May 1992
Some examples are now given. Note the arrows which indicate
asymmetrical mappings:
PrintableString ASCII
'a demo.' <-> 'a demo.'
foo(a)bar <-> foo@bar
(q)(u)(p)(q) <-> "_%"
(a) <-> @
(A) -> @
(l)a(r) <-> (a)
(126) <-> ~
( -> (
(l) <-> (
Chapter 4 - Addressing
Addressing is probably the trickiest problem of an X.400 <-> RFC 822
gateway. Therefore it is given a separate chapter. This chapter, as
a side effect, also defines a textual representation of an X.400 O/R
Address.
Initially we consider an address in the (human) mail user sense of
"what is typed at the mailsystem to reference a mail user". A basic
RFC 822 address is defined by the EBNF EBNF.822-address:
822-address = [ route ] addr-spec
In an 822-MTS protocol, the originator and each recipient are
considered to be defined by such a construct. In an RFC 822 header,
the EBNF.822-address is encapsulated in the 822.address syntax rule,
and there may also be associated comments. None of this extra
information has any semantics, other than to the end user.
The basic X.400 O/R Address, used by the MTS for routing, is defined
by MTS.ORAddress. In IPMS, the MTS.ORAddress is encapsulated within
IPMS.ORDescriptor.
It can be seen that RFC 822 822.address must be mapped with
IPMS.ORDescriptor, and that RFC 822 EBNF.822-address must be mapped
with MTS.ORAddress.
4.1. A textual representation of MTS.ORAddress
MTS.ORAddress is structured as a set of attribute value pairs. It is
clearly necessary to be able to encode this in ASCII for gatewaying
purposes. All components shall be encoded, in order to guarantee
return of error messages, and to optimise third party replies.
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4.2. Basic Representation
An O/R Address has a number of structured and unstructured
attributes. For each unstructured attribute, a key and an encoding
is specified. For structured attributes, the X.400 attribute is
mapped onto one or more attribute value pairs. For domain defined
attributes, each element of the sequence will be mapped onto a triple
(key and two values), with each value having the same encoding. The
attributes are as follows, with 1984 attributes given in the first
part of the table. For each attribute, a reference is given,
consisting of the relevant sections in X.402 / ISO 10021-2, and the
extension identifier for 88 only attributes:
Attribute (Component) Key Enc Ref Id
84/88 Attributes
MTS.CountryName C P 18.3.3
MTS.AdministrationDomainName ADMD P 18.3.1
MTS.PrivateDomainName PRMD P 18.3.21
MTS.NetworkAddress X121 N 18.3.7
MTS.TerminalIdentifier T-ID 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
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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 21
MTS.ExtendedNetworkAddress
.e163-4-address.number NET-NUM N 18.3.7 22
MTS.ExtendedNetworkAddress
.e163-4-address.sub-address NET-SUB N 18.3.7 22
MTS.ExtendedNetworkAddress
.psap-address NET-PSAP X 18.3.7 22
MTS.TerminalType T-TY I 18.3.24 23
The following keys identify different EBNF encodings, which are
associated with the ASCII representation of MTS.ORAddress.
Key Encoding
P printablestring
N numericstring
T teletex-string
P/T teletex-and-or-ps
I labelled-integer
X presentation-address
The BNF for presentation-address is taken from the specification "A
String Encoding of Presentation Address" [Kille89a].
In most cases, the EBNF encoding maps directly to the ASN.1 encoding
of the attribute. There are a few exceptions. In cases where an
attribute can be encoded as either a PrintableString or NumericString
(Country, ADMD, PRMD), either form is mapped into the BNF. When
generating ASN.1, the NumericString encoding shall be used if the
string contains only digits.
There are a number of cases where the P/T (teletex-and-or-ps)
representation is used. Where the key maps to a single attribute,
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this choice is reflected in the encoding of the attribute (attributes
10-21). For most of the 1984 attributes and common name, there is a
printablestring and a teletex variant. This pair of attributes is
mapped onto the single component here. This will give a clean
mapping for the common cases where only one form of the name is used.
Recently, ISO has undertaken work to specify a string form of O/R
Address [CCITT/ISO91a]. This has specified a number of string
keywords for attributes. As RFC 1148 was an input to this work, many
of the keywords are the same. To increase compatability, 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 NUMBER
When 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 will be treated as ordered values of OU.
4.2.1. Encoding of Personal Name
Handling of Personal Name and Teletex Personal Name based purely on
the EBNF.standard-type syntax defined above is likely to be clumsy.
It seems desirable to utilise the "human" conventions for encoding
these components. A syntax is defined, which is designed to provide
a clean encoding for the common cases of O/R Address specification
where:
1. There is no generational qualifier
2. Initials contain only letters
3. Given Name does not contain full stop ("."), and is at least
two characters long.
4. Surname does not contain full stop in the first two
characters.
5 If Surname is the only component, it does not contain full
stop.
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The following EBNF is defined:
encoded-pn = [ given "." ] *( initial "." ) surname
given = 2*<ps-char not including ".">
initial = ALPHA
surname = printablestring
This is used to map from any string containing only printable string
characters to an O/R address personal name. To map from a string to
O/R Address components, parse the string according to the EBNF. The
given name and surname are assigned directly. All EBNF.initial
tokens are concatenated without intervening full stops to generate
the initials component.
For an O/R address which follows the above restrictions, a string is
derived in the natural manner. In this case, the mapping will be
reversible.
For example:
GivenName = "Marshall"
Surname = "Rose"
Maps with "Marshall.Rose"
Initials = "MT"
Surname = "Rose"
Maps with "M.T.Rose"
GivenName = "Marshall"
Initials = "MT"
Surname = "Rose"
Maps with "Marshall.M.T.Rose"
Note that X.400 suggest that Initials is used to encode ALL initials.
Therefore, the defined encoding is "natural" when either GivenName or
Initials, but not both, are present. The case where both are present
can be encoded, but this appears to be contrived!
4.2.2. Standard Encoding of MTS.ORAddress
Given this structure, we can specify a BNF representation of an O/R
Address.
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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 = "$" ps-char
The standard-type is any key defined in the table in Section 4.2,
except PN, and DD. The BNF leads to a set of attribute/value pairs.
The value is interpreted according to the EBNF encoding defined in
the table.
If the standard-type is PN, the value is interpreted according to
EBNF.encoded-pn, and the components of MTS.PersonalName and/or
MTS.TeletexPersonalName derived accordingly.
If dd-key is the recognised Domain Defined string (DD), then the type
and value are interpreted according to the syntax implied from the
encoding, and aligned to either the teletex or printable string form.
Key and value shall have the same encoding.
If value is "RFC-822", then the (printable string) Domain Defined
Type of "RFC-822" is assumed. This is an optimised encoding of the
domain defined type defined by this specification.
The matching of all keywords shall be done in a case-independent
manner.
EBNF.std-or-address uses the characters "/" and "=" as delimiters.
Domain Defined Attributes and any value may contain these characters.
A quoting mechanism, using the non-printable string "$" is used to
allow these characters to be represented.
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
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accordingly. This restriction maximises the syntax checking which
can be done at a gateway.
4.3. EBNF.822-address <-> MTS.ORAddress
Ideally, the mapping specified would be entirely symmetrical and
global, to enable addresses to be referred to transparently in the
remote system, with the choice of gateway being left to the Message
Transfer Service. There are two fundamental reasons why this is not
possible:
1. The syntaxes are sufficiently different to make this
awkward.
2. In the general case, there would not be the necessary
administrative co-operation between the X.400 and RFC 822
worlds, which would be needed for this to work.
Therefore, an asymmetrical mapping is defined, which can be
symmetrical where there is appropriate administrative control.
4.3.1. X.400 encoded in RFC 822
The std-or-address syntax is used to encode O/R Address information
in the 822.local-part of EBNF.822-address. In some cases, further
O/R Address information is associated with the 822.domain component.
This cannot be used in the general case, due to character set
problems, and to the variants of X.400 O/R Addresses which use
different attribute types. The only way to encode the full
PrintableString character set in a domain is by use of the
822.domain-ref syntax (i.e. 822.atom). This is likely to cause
problems on many systems. The effective character set of domains is
in practice reduced from the RFC 822 set, by restrictions imposed by
domain conventions and policy, and by restrictions in RFC 821.
A generic 822.address consists of a 822.local-part and a sequence of
822.domains (e.g., <@domain1,@domain2:user@domain3>). All except the
822.domain associated with the 822.local-part (domain3 in this case)
are considered to specify routing within the RFC 822 world, and will
not be interpreted by the gateway (although they may have identified
the gateway from within the RFC 822 world).
The 822.domain associated with the 822.local-part identifies the
gateway from within the RFC 822 world. This final 822.domain may be
used to determine some number of O/R Address attributes, where this
does not conflict with the first role. RFC 822 routing to gateways
will usually be set up to facilitate the 822.domain being used for
both purposes. The following O/R Address attributes are considered
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as a hierarchy, and may be specified by the domain. They are (in
order of hierarchy):
Country, ADMD, PRMD, Organisation, Organisational Unit
There may be multiple Organisational Units.
A global mapping is defined between domain specifications, and some
set of attributes. This association proceeds hierarchically. For
example, if a domain implies ADMD, it also implies country.
Subdomains under this are associated according to the O/R Address
hierarchy. For example:
=> "AC.UK" might be associated with
C="GB", ADMD="GOLD 400", PRMD="UK.AC"
then domain "R-D.Salford.AC.UK" maps with
C="GB", ADMD="GOLD 400", PRMD="UK.AC", O="Salford", OU="R-D"
There are three basic reasons why a domain/attribute mapping might be
maintained, as opposed to using simply subdomains:
1. As a shorthand to avoid redundant X.400 information. In
particular, there will often be only one ADMD per country,
and so it does not need to be given explicitly.
2. To deal with cases where attribute values do not fit the
syntax:
domain-syntax = alphanum [ *alphanumhyphen alphanum ]
alphanum = <ALPHA or DIGIT>
alphanumhyphen = <ALPHA or DIGIT or HYPHEN>
Although RFC 822 allows for a more general syntax, this
restricted syntax is chosen as it is the one chosen by the
various domain service administrations.
3. To deal with missing elements in the hierarchy. A domain
may be associated with an omitted attribute in conjunction
with several present ones. When performing the algorithmic
insertion of components lower in the hierarchy, the omitted
value shall be skipped. For example, if "HNE.EGM" is
associated with "C=TC", "ADMD=ECQ", "PRMD=HNE", and omitted
organisation, then "ZI.HNE.EGM" is mapped with "C=TC",
"ADMD=ECQ", "PRMD=HNE", "OU=ZI". Attributes may have null
values, and this is treated separately from omitted
attributes (whilst it would be bad practice to treat these
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two cases differently, they must be allowed for).
This set of mappings needs be known by the gateways relaying between
the RFC 822 world, and the O/R Address space associated with the
mapping in question. There needs to be a single global definition of
this set of mappings. A mapping implies an adminstrative equivalence
between the two parts of the namespaces which are mapped together.
To correctly route in all cases, it is necessary for all gateways to
know the mapping. To facilitate distribution of a global set of
mappings, a format for the exchange of this information is defined in
Appendix F.
The remaining attributes are encoded on the LHS, using the EBNF.std-
or-address syntax. For example:
/I=J/S=Linnimouth/GQ=5/@Marketing.Widget.COM
encodes the MTS.ORAddress consisting of:
MTS.CountryName = "TC"
MTS.AdministrationDomainName = "BTT"
MTS.OrganizationName = "Widget"
MTS.OrganizationalUnitNames.value = "Marketing"
MTS.PersonalName.surname = "Linnimouth"
MTS.PersonalName.initials = "J"
MTS.PersonalName.generation-qualifier = "5"
The first three attributes are determined by the domain Widget.COM.
Then, the first element of OrganizationalUnitNames is determined
systematically, and the remaining attributes are encoded on the LHS.
In an extreme case, all of the attributes will be on the LHS. As the
domain cannot be null, the RHS will simply be a domain indicating the
gateway.
The RHS (domain) encoding is designed to deal cleanly with common
addresses, and so the amount of information on the RHS 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. Use of other forms of O/R Address, and teletex encoded
attributes will require an LHS encoding.
There is a further mechanism to simplify the encoding of common
cases, where the only attributes to be encoded on the LHS is a (non-
Teletex) Personal Name attributes which comply with the restrictions
of 4.2.1. To achieve this, the 822.local-part shall be encoded as
EBNF.encoded-pn. In the previous example, if the GenerationQualifier
was not present in the previous example O/R Address, it would map
with the RFC 822 address: J.Linnimouth@Marketing.Widget.COM.
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From the standpoint of the RFC 822 Message Transfer System, the
domain specification is simply used to route the message in the
standard manner. The standard domain mechanisms are used to select
appropriate gateways for the corresponding O/R Address space. In
most cases, this will be done by registering the higher levels, and
assuming that the gateway can handle the lower levels.
4.3.2. RFC 822 encoded in X.400
In some cases, the encoding defined above may be reversed, to give a
"natural" encoding of genuine RFC 822 addresses. This depends
largely on the allocation of appropriate management domains.
The general case is mapped by use of domain defined attributes. A
Domain defined type "RFC-822" is defined. The associated attribute
value is an ASCII string encoded according to Section 3.3.3 of this
specification. The interpretation of the ASCII string depends on the
context of the gateway.
1. In the context of RFC 822, and RFC 920
[Crocker82a,Postel84a], the string can be used directly.
2. In the context of the JNT Mail protocol, and the NRS
[Kille84a,Larmouth83a], the string shall be interpreted
according to Mailgroup Note 15 [Kille84b].
3. In the context of UUCP based systems, the string shall be
interpreted as defined in [Horton86a].
Other O/R Address attributes will be used to identify a context in
which the O/R Address will be interpreted. This might be a
Management Domain, or some part of a Management Domain which
identifies a gateway MTA. For example:
C = "GB"
ADMD = "GOLD 400"
PRMD = "UK.AC"
O = "UCL"
OU = "CS"
"RFC-822" = "Jimmy(a)WIDGET-LABS.CO.UK"
OR
C = "TC"
ADMD = "Wizz.mail"
PRMD = "42"
"rfc-822" = "postel(a)venera.isi.edu"
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Note in each case the PrintableString encoding of "@" as "(a)". In
the second example, the "RFC-822" domain defined attribute is
interpreted everywhere within the (Private) Management Domain. In
the first example, further attributes are needed within the
Management Domain to identify a gateway. Thus, this scheme can be
used with varying levels of Management Domain co-operation.
There is a limit of 128 characters in the length of value of a domain
defined attribute, and an O/R Address can have a maxmimum of four
domain defined attributes. Where the printable string generated from
the RFC 822 address exceeeds this value, additional domain defined
attributes are used to enable up to 512 characters to 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.
There is, analagous with 4.3.1, a means to associate parts of the O/R
Address hierarchy with domains. There is an analogous global
mapping, which in most cases will be the inverse of the domain to O/R
address mapping. The mapping is maintained separately, as there may
be differences (e.g., two alternate domain names map to the same set
of O/R address components).
4.3.3. Component Ordering
In most cases, ordering of O/R Address components is not significant
for the mappings specified. However, Organisational Units (printable
string and teletex forms) and Domain Defined Attributes are specified
as SEQUENCE in MTS.ORAddress, and so their order may be significant.
This specification needs to take account of this:
1. To allow consistent mapping into the domain hierarchy
2. To ensure preservation of order over multiple mappings.
There are three places where an order is specified:
1. The text encoding (std-or-address) of MTS.ORAddress as used
in the local-part of an RFC 822 address. An order is needed
for those components which may have multiple values
(Organisational Unit, and Domain Defined Attributes). When
generating an 822.std-or-address, components of a given type
shall be in hierarchical order with the most significant
component on the RHS. If there is an Organisation
Attribute, it shall be to the right of any Organisational
Unit attributes. These requirements are for the following
reasons:
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- Alignment to the hierarchy of other components in RFC
822 addresses (thus, Organisational Units will appear
in the same order, whether encoded on the RHS or LHS).
Note the differences of JNT Mail as described in
Appendix B.
- Backwards compatibility with RFC 987/1026.
- To ensure that gateways generate consistent addresses.
This is both to help end users, and to generate
identical message ids.
Further, it is recommended that all other attributes are
generated according to this ordering, so that all attributes
so encoded follow a consistent hierarchy. When generating
822.msg-id, this order shall be followed.
2. For the Organisational Units (OU) in MTS.ORAddress, the
first OU in the SEQUENCE is the most significant, as
specified in X.400.
3. For the Domain Defined Attributes in MTS.ORAddress, the
First Domain Defined Attribute in the SEQUENCE is the most
significant.
Note that although this ordering is mandatory for this
mapping, there are NO implications on ordering significance
within X.400, where this is a Management Domain issue.
4.3.4. RFC 822 -> X.400
There are two basic cases:
1. X.400 addresses encoded in RFC 822. This will also include
RFC 822 addresses which are given reversible encodings.
2. "Genuine" RFC 822 addresses.
The mapping shall proceed as follows, by first assuming case 1).
STAGE I.
1. If the 822-address is not of the form:
local-part "@" domain
take the domain which will be routed on and apply step 2 of
stage 1 to derive (a possibly null) set of attributes. Then
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go to stage II.
NOTE:It may be appropriate to reduce a source route address
to this form by removal of all bar the last domain. In
terms of the design intentions of RFC 822, this would
be an incorrect action. However, in most real cases,
it will do the "right" thing and provide a better
service to the end user. This is a reflection on the
excessive and inappropriate use of source routing in
RFC 822 based systems. Either approach, or the
intermediate approach of stripping only domain
references which reference the local gateway are
conformant to this specification.
2. Attempt to parse EBNF.domain as:
*( domain-syntax "." ) known-domain
Where EBNF.known-domain is the longest possible match in 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 exceed 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.
3. If the 822.local-part uses the 822.quoted-string encoding,
remove this quoting. If this unquoted 822.local-part has
leading space, trailing space, or two adjacent space go to
stage II.
4. If the unquoted 822.local-part contains any characters not
in PrintableString, go to stage II.
5. Parse the (unquoted) 822.local-part according to the EBNF
EBNF.std-or-address. Checking of upper bounds should not be
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done at this point. If this parse fails, parse the local-
part according to the EBNF EBNF.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 dericed attributes which
are more significant thant the most signicant 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). therwise add LHS and RHS
derived attributes together.
6. Associate the EBNF.attribute-value syntax (determined from
the identified type) with each value, and check that it
conforms. If not, go to stage II.
7. Ensure that the set of attributes conforms both to the
MTS.ORAddress specification 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.
8. 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.
1. Convert the EBNF.822-address to PrintableString, as
specified in Chapter 3.
2. Generate the "RFC-822" domain defined attribute from this
string.
3. 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
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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 throug 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, which are 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
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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:
1. Ignore the omission of a trailing "/" in the std-or syntax.
2. If there is no ADMD component, and both country and PRMD are
present, the value of /ADMD= / (single space) is assumed.
3. 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:
4. 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:
1. RFC 822 addresses encoded in X.400.
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2. "Genuine" X.400 addresses. This may include symmetrically
encoded RFC 822 addresses.
When a MTS Recipient O/R Address is interpreted, gatewaying will be
selected if there 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
1. Contain the special attribute.
AND
2. Identifies the local gateway or any other known gateway with
the other attributes.
use mapping A. In other cases, use mapping B.
NOTE:
A pragmatic approach would be to assume that any O/R
Address with the special domain defined attribute identifies
an RFC 822 address. This will usually work correctly, but is
in principle not correct. Use of this approach is
conformant to this specification.
Mapping A
1. Map the domain defined attribute value to ASCII, as defined
in Chapter 3.
Mapping B
This is used for X.400 addresses which do not use the explicit RFC
822 encoding.
1. For all string encoded attributes, remove any leading or
trailing spaces, and replace adjacent spaces with a single
space.
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-address mapping is used as in 4), then the
orginal values should be used.
2. Map numeric country codes to the two letter values.
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3. 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 analagous 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.
4. 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, as 822.local-part cannot be null. If there are
omitted attributes in the O/R address prefix, these will
have correctly and uniquely mapped 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 the is an addres /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.
5. 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-address syntax, 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
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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; "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
There are two types of repeated mapping:
1. A recursive mapping, where the repeat is within one gateway
2 A source route, where the repetition occurs across multiple
gateways
4.4.1. Recursive Mappings
It is possible to supply an address which is recurive 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, that no unnecessary protocol
conversion occurs. This will minimise 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
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received message will have the originator and any 3rd party X.400 O/R
Addresses in correct format (rather than doubly encoded). In cases
(X.400 or RFC 822) where there is common agreement on gateway
identification, then this will apply to multiple gateways.
When a message traverses multiple gateways, the mapping will always
be reversible, in that a reply can be generated which will correctly
reverse the path. In many cases, the mapping will also be
symmetrical, which will appear clean to the end user. For example,
if countries "AB" and "XY" have RFC 822 networks, but are
interconnected by X.400, the following may happen: The originator
specifies:
Joe.Soap@Widget.PTT.XY
This is routed to a gateway, which generates:
C = "XY"
ADMD = "PTT"
PRMD = "Griddle MHS Providers"
Organisation = "Widget Corporation"
Surname = "Soap"
Given Name = "Joe"
This is then routed to another gateway where the mapping is reversed
to give:
Joe.Soap@Widget.PTT.XY
Here, use of the gateway is transparent.
Mappings will only be symmetrical where mapping tables are defined.
In other cases, the reversibility is more important, due to the (far
too frequent) cases where RFC 822 and X.400 services are partitioned.
The syntax may be used to source route. THIS IS STRONGLY
DISCOURAGED. For example:
X.400 -> RFC 822 -> X.400
C = "UK"
ADMD = "Gold 400"
PRMD = "UK.AC"
"RFC-822" = "/PN=Duval/DD.Title=Manager/(a)Inria.ATLAS.FR"
This will be sent to an arbitrary UK Academic Community gateway by
X.400. Then it will be sent by JNT Mail to another gateway
determined by the domain Inria.ATLAS.FR (FR.ATLAS.Inria). This will
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then derive the X.400 O/R Address:
C = "FR"
ADMD = "ATLAS"
PRMD = "Inria"
PN.S = "Duval"
"Title" = "Manager"
Similarly:
RFC 822 -> X.400 -> RFC 822
"/C=UK/ADMD=BT/PRMD=AC/RFC-822=jj(a)seismo.css.gov/"@monet.berkeley.edu
This will be sent to monet.berkeley.edu by RFC 822, then to the AC
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 recipient
822-MTS recipients and return addresses are encoded as EBNF.822-
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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 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).
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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
Not all per-recipient information can be passed at the 822-MTS level.
For this reason, two new RFC 822 headers are created, in order to
carry this information to the RFC 822 recipient. These fields are
"X400-Originator:" and "X400-Recipients:".
The "X400-Originator:" field is set to the same value as the 822-MTS
originator. In addition, if
MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName) contains
MTS.ORName.directory-name then this Directory Name shall be
represented in an 822.comment.
Recipient names, taken from each value of
MTS.OtherMessageDeliveryFields.this-recipient-name and
MTS.OtherMessageDeliveryFields.other-recipient-names are made
available to the RFC 822 user by use of the "X400-Recipients:" field.
By taking the recipients at the MTS level, disclosure of recipients
will be dealt with correctly. However, this conflicts with a desire
to optimise mail transfer. There is no problem when disclosure of
recipients is allowed. Similarly, there is no problem if there is
only one RFC 822 recipient, as the "X400-Recipients field is only
given one address.
There is a problem if there are multiple RFC 822 recipients, and
disclosure of recipients is prohibited. Two options are allowed:
1. Generate one copy of the message for each RFC 822 recipient,
with the "X400-Recipients field correctly set to the
recipient of that copy. This is functionally correct, but
is likely to be more expensive.
2. Discard the per-recipient information, and insert a field:
X400-Recipients: non-disclosure:;
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This 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.
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 information associated with this is
represented by the "DL-Expansion-History:" field descrined in Section
5.3.6. Other information is represented in an 822.comment associated
associated with MTS.OtherMessageDeliveryFields.this-recipient-name,
The message may be delivered to different RFC 822 recipients, and so
several addresses in the "X400-Recipients:" field may have such
comments. The non-commented recipient 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 is derived from
MTA.PerRecipientMessageTransferFields.extension.redirection-history.
An example of this is:
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 are represented in comments
if they are used. None of these services can be provided on RFC 822
networks, and so in general these will be informative strings
associated with other MTS recipients. In some cases, string values
are defined. For the remainder, the string value shall be chosen by
the implementor. If the parameter has a default value, then no
comment shall be inserted when the parameter has that default value.
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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, this shall be generated by
the gateway. Supplementary Information shall be set to indicate that
the report is gateway generated. This information shall include the
name of the gateway generating the report.
4.6.3. Message IDs (MTS)
A mapping from 822.msg-id to MTS.MTSIdentifier is defined. The
reverse mapping is not needed, as MTS.MTSIdentifier is always mapped
onto new RFC 822 fields. The value of MTS.MTSIdentifier.local-part
will facilitate correlation of gateway errors.
To map from 822.msg-id, apply the standard mapping to 822.msg-id, in
order to generate an MTS.ORAddress. The Country, ADMD, and PRMD
components of this are used to generate MTS.MTSIdentifier.global-
domain-identifier. MTS.MTSIdentifier.local-identifier is set to the
822.msg-id, including the braces "<" and ">". If this string is
longer than MTS.ub-local-id-length (32), then it is truncated to this
length.
The reverse mapping is not used in this specification. It would be
applicable where MTS.MTSIdentifier.local-identifier is of syntax
822.msg-id, and it algorithmically identifies MTS.MTSIdentifier.
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4.7. IPMS Mappings
All RFC 822 addresses are assumed to use the 822.mailbox syntax.
This 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 is used within the IPMS.ORDescriptor, IPMS.RecipientSpecifier,
and IPMS.IPMIdentifier. An asymmetrical mapping is defined between
these components.
4.7.1. RFC 822 -> X.400
To derive IPMS.ORDescriptor from an RFC 822 address.
1. Take the address, and extract an EBNF.822-address. This can
be derived trivially from either the 822.addr-spec or
822.route-addr syntax. This is mapped to MTS.ORName as
described above, and used as IMPS.ORDescriptor.formal-name.
2. A string shall be built consisting of (if present):
- The 822.phrase component if the 822.address is an
822.phrase 822.route-addr construct.
- Any 822.comments, in order, retaining the parentheses.
This string is then encoded into T.61 use a human oriented
mapping (as described in Chapter 3). If the string is not
null, it is assigned to IPMS.ORDescri | ||||||
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