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1138 Mapping between X.Dec-01-1989 Status: EXPERIMENTAL 1138 Mapping between X.400(1988) / ISO 10021 and RFC 822. S.E. Kille.Dec-01-1989. (Format: TXT=191029 bytes) (Obsoleted by RFC1327,RFC1495, RFC2156) (Updates RFC0822, RFC0987, RFC1026) (Updated byRFC1148) (Status: EXPERIMENTAL)
Network Working Group S. Kille
Request for Comments 1138 University College London
Updates: RFCs 822, 987, 1026 December 1989
Mapping between X.400(1988) / ISO 10021 and RFC 822
Status of this Memo
This RFC suggests an electronic mail protocol mapping for the
Internet community and UK Academic Community, and requests discussion
and suggestions for improvements. This memo does not specify an
Internet standard. Distribution of this memo is unlimited.
This document describes a set of mappings which will enable
interworking between systems operating the CCITT X.400 (1988)
Recommendations on Message Handling Systems / ISO IEC 10021 Message
Oriented Text Interchange Systems (MOTIS) [CCITT/ISO88a], and systems
using the RFC 822 mail protocol [Crocker82a] or protocols derived
from RFC 822. The approach aims to maximise the services offered
across the boundary, whilst not requiring unduly complex mappings.
The mappings should not require any changes to end systems.
This document is based on RFC 987 and RFC 1026 [Kille86a, Kille87a],
which define a similar mapping for X.400 (1984). This document does
not obsolete the earlier ones, as its domain of application is
different.
Specification
This document specifies a mapping between two protocols. This
specification should be used when this mapping is performed on the
Internet or in the UK Academic Community. This specification may be
modified in the light of implementation experience, but no
substantial changes are expected.
Table of Contents
1. Overview ............................................... 2
1.1 X.400 ................................................. 2
1.2 RFC 822 ............................................... 3
1.3 The need for conversion ............................... 4
1.4 General approach ...................................... 4
1.5 Gatewaying Model ...................................... 5
1.6 RFC 987 ............................................... 7
1.7 Aspects not covered ................................... 8
1.8 Subsetting ............................................ 9
1.9 Document Structure .................................... 9
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RFC 1138 Mapping X.400(88) and 822 December 1989
1.10 Acknowledgements ..................................... 10
2. Service Elements ....................................... 10
2.1 The Notion of Service Across a Gateway ................ 10
2.2 RFC 822 ............................................... 11
2.3 X.400 ................................................. 15
3. Basic Mappings ........................................ 24
3.1 Notation .............................................. 24
3.2 ASCII and IA5 ......................................... 25
3.3 Standard Types ........................................ 25
3.4 Encoding ASCII in Printable String .................... 28
4. Addressing ............................................. 29
4.1 A textual representation of MTS.ORAddress ............. 30
4.2 Basic Representation .................................. 30
4.3 EBNF.822-address <-> MTS.ORAddress .................... 34
4.4 Repeated Mappings ..................................... 43
4.5 Directory Names ....................................... 45
4.6 MTS Mappings .......................................... 45
4.7 IPMS Mappings ....... ................................. 48
5. Detailed Mappings ...................................... 52
5.1 RFC 822 -> X.400 ...................................... 52
5.2 Return of Contents .................................... 59
5.3 X.400 -> RFC 822 ...................................... 60
Appendix A Differences with RFC 987 ....................... 78
1. Introduction ........................................... 78
2. Service Elements ....................................... 78
3. Basic Mappings ......................................... 78
4. Addressing ............................................. 78
5. Detailed Mappings ...................................... 79
6. Appendices ............................................. 79
Appendix B Mappings specific to the JNT Mail .............. 79
1. Introduction ........................................... 79
2. Domain Ordering ........................................ 79
3. Acknowledge-To: ........................................ 79
4. Trace .................................................. 80
5. Timezone specification ................................. 80
6. Lack of 822-MTS originator specification ............... 80
Appendix C Mappings specific to UUCP Mail ................. 81
Appendix D Object Identifier Assignment ................... 82
Appendix E BNF Summary .................................... 82
Appendix F Format of address mapping tables ............... 89
References ................................................. 91
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
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(MOTIS). This ISO/CCITT standard is referred to in this document as
"X.400", which is a convenient shorthand. Any reference to the 1984
CCITT Recommendations will be explicit. X.400 defines an
Interpersonal Messaging System (IPMS), making use of a store and
forward Message Transfer System. This document relates to the IPMS,
and not to wider application of X.400. It is expected that X.400
will be implemented very widely.
1.2. RFC 822
RFC 822 is the current specification of the messaging standard on the
Internet. This standard evolved with the evolution of the network
from the ARPANET (created by the Defense Advanced Research Projects
Agency) to the Internet, which now involves over 1000 networks and is
sponsored by DARPA, NSF, DOE, NASA, and NIH. It specifies an end to
end message format. It is used in conjunction with a number of
different message transfer protocol environments.
SMTP Networks
On the Internet and other TCP/IP networks, RFC 822 is used in
conjunction with two other standards: RFC 821, also known as
Simple Mail Transfer Protocol (SMTP) [Postel82a], and RFC 1034
which is a Specification for domains and a distributed name
service [Mockapetris87a].
UUCP Networks
UUCP is the UNIX to UNIX CoPy protocol, which is usually used
over dialup telephone networks to provide a simple message
transfer mechanism. There are some extensions to RFC 822,
particularly in the addressing. They use domains which conform
to RFC 1034, but not the corresponding domain nameservers
[Horton86a].
Csnet
Some portions of Csnet follow the Internet protocols. The
dialup portion of Csnet uses the Phonenet protocols as a
replacement for RFC 821. This portion uses domains which
conform to RFC 1034, but not the corresponding domain
nameservers.
Bitnet
Some parts of Bitnet and related networks use RFC 822 related
protocols, with EBCDIC encoding.
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JNT Mail Networks
A number of X.25 networks, particularly those associated with
the UK Academic Community, use the JNT (Joint Network Team)
Mail Protocol, also known as Greybook [Kille84a]. This is used
with domains and name service specified by the JNT NRS (Name
Registration Scheme) [Larmouth83a].
The mappings specified here are appropriate for all of these
networks.
1.3. The need for conversion
There is a large community using RFC 822 based protocols for mail
services, who will wish to communicate with users of the IPMS
provided by X.400 systems. This will also be a requirement in cases
where communities intend to make a transition to use of an X.400
IPMS, as conversion will be needed to ensure a smooth service
transition. It is expected that there will be more than one gateway,
and this specification will enable them to behave in a consistent
manner. Note that the term gateway is used to describe a component
performing the protocol mappings between RFC 822 and X.400. This is
standard usage amongst mail implementors, but should be noted
carefully by transport and network service implementors.
Consistency between gateways is desirable to provide:
1. Consistent service to users.
2. The best service in cases where a message passes through
multiple gateways.
1.4. General approach
There are a number of basic principles underlying the details of the
specification. These principles are goals, and are not achieved in
all aspects of the specification.
1. The specification should be pragmatic. There should not be
a requirement for complex mappings for "Academic" reasons.
Complex mappings should not be required to support trivial
additional functionality.
2. Subject to 1), functionality across a gateway should be as
high as possible.
3. It is always a bad idea to lose information as a result of
any transformation. Hence, it is a bad idea for a gateway
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to discard information in the objects it processes. This
includes requested services which cannot be fully mapped.
4. All mail gateways actually operate at exactly one level
above the layer on which they conceptually operate. This
implies that the gateway must not only be cognisant of the
semantics of objects at the gateway level, but also be
cognisant of higher level semantics. If meaningful
transformation of the objects that the gateway operates on
is to occur, then the gateway needs to understand more than
the objects themselves.
5. The specification should be reversible. That is, a double
transformation should bring you back to where you started.
1.5. Gatewaying Model
1.5.1. X.400
X.400 defines the IPMS Abstract Service in X.420/ISO 10021-7,
[CCITT/ISO88b] which comprises of three basic services:
1. Origination
2. Reception
3. Management
Management is a local interaction between the user and the IPMS, and
is therefore not relevant to gatewaying. The first two services
consist of operations to originate and receive the following two
objects:
1. IPM (Interpersonal Message). This has two components: a
heading, and a body. The body is structured as a sequence
of body parts, which may be basic components (e.g., IA5
text, or G3 fax), or IP Messages. The heading consists of
fields containing end to end user information, such as
subject, primary recipients (To:), and importance.
2. IPN (Inter Personal Notification). A notification about
receipt of a given IPM at the UA level.
The Origination service also allows for origination of a probe, which
is an object to test whether a given IPM could be correctly received.
The Reception service also allows for receipt of Delivery Reports
(DR), which indicate delivery success or failure.
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These IPMS Services utilise the Message Transfer (MT) Abstract
Service [CCITT/ISO88c]. The MT Abstract Service provides the
following three basic services:
1. Submission (used by IPMS Origination)
2. Delivery (used by IPMS Reception)
3. Administration (used by IPMS Management)
Administration is a local issue, and so does not affect this
standard. Submission and delivery relate primarily to the MTS
Message (comprising Envelope and Content), which carries an IPM or
IPN (or other uninterpreted contents). There is also an Envelope,
which includes an ID, an originator, and a list of recipients.
Submission also includes the probe service, which supports the IPMS
Probe. Delivery also includes Reports, which indicate whether a
given MTS Message has been delivered or not.
The MTS is REFINED into the MTA (Message Transfer Agent) Service,
which define the interaction between MTAs, along with the procedures
for distributed operation. This service provides for transfer of MTS
Messages, Probes, and Reports.
1.5.2. RFC 822
RFC 822 is based on the assumption that there is an underlying
service, which is here called the 822-MTS service. The 822-MTS
service provides three basic functions:
1. Identification of a list of recipients.
2. Identification of an error return address.
3. Transfer of an RFC 822 message.
It is possible to achieve 2) within the RFC 822 header. Some 822-MTS
protocols, in particular SMTP, can provide additional functionality,
but as these are neither mandatory in SMTP, nor available in other
822-MTS protocols, they are not considered here. Details of aspects
specific to two 822-MTS protocols are given in Appendices B and C.
An RFC 822 message consists of a header, and content which is
uninterpreted ASCII text. The header is divided into fields, which
are the protocol elements. Most of these fields are analogous to P2
heading fields, although some are analogous to MTS Service Elements
or MTA Service Elements.
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1.5.3. The Gateway
Given this functional description of the two services, the functional
nature of a gateway can now be considered. It would be elegant to
consider the 822-MTS service mapping onto the MTS Service Elements
and RFC 822 mapping onto an IPM, but reality just does not fit.
Another elegant approach would be to treat this document as the
definition of an X.400 Access Unit (AU). Again, reality does not
fit. It is necessary to consider that the IPM format definition, the
IPMS Service Elements, the MTS Service Elements, and MTA Service
Elements on one side are mapped into RFC 822 + 822-MTS on the other
in a slightly tangled manner. The details of the tangle will be made
clear in Chapter 5. Access to the MTA Service Elements is minimised.
The following basic mappings are thus defined. When going from RFC
822 to X.400, an RFC 822 message and the associated 822-MTS
information is always mapped into an IPM (MTA, MTS, and IPMS
Services). Going from X.400 to RFC 822, an RFC 822 message and the
associated 822-MTS information may be derived from:
1. A Report (MTA, and MTS Services)
2. An IPN (MTA, MTS, and IPMS Services)
3. An IPM (MTA, MTS, and IPMS Services)
Probes (MTA Service) must be processed by the gateway, as discussed
in Chapter 5. MTS Messages containing Content Types other than those
defined by the IPMS are not mapped by the gateway, and should be
rejected at the gateway.
1.5.4. Repeated Mappings
The mappings specified here are designed to work where a message
traverses multiple times between X.400 and RFC 822. This is often
essential, particularly in the case of distribution lists. However,
in general, this will lead to a level of service which is the lowest
common denominator (approximately the services offered by RFC 822).
In particular, there is no expectation of additional X.400 services
being mapped - although this may be possible in some cases.
1.6. RFC 987
Much of this work is based on the initial specification of RFC 987
and in its addendum RFC 1026. A basic decision is that the mapping
will be to the full 1988 version of X.400, and not to a 1984
compatible subset. This is important, to give good support to
communities which will utilise full X.400 at an early date. This has
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the following implications:
- This document does not obsolete RFC 987, as it has a
different domain of application.
- If a gatewayed message is being transferred to a 1984
system, then RFC 987 should be used. If the X.400 side of
the gateway is a 1988 system, then it should be operated in
1984 compatibility mode. There is no advantage and some
disadvantage in using the new mapping, and later on applying
X.400 downgrading rules. Note that in an environment where
RFC 822 is of major importance, it may be desirable for
downgrading to consider the case where the message was
originated in an RFC 822 system, and mapped according to
this specification.
- New features of X.400 can be used to provide a much cleaner
mapping than that defined in RFC 987.
Unnecessary change is usually a bad idea. Changes on the RFC 822
side are avoided as far as possible, so that RFC 822 users do not see
arbitrary differences between systems conforming to this
specification, and those following RFC 987. Changes on the X.400
side are minimised, but are more acceptable, due to the mapping onto
a new set of services and protocols.
A summary of changes made is given in Appendix A.
1.7. Aspects not covered
There have been a number of cases where RFC 987 was used in a manner
which was not intended. This section is to make clear some
limitations of scope. In particular, this specification does not
specify:
- Extensions of RFC 822 to provide access to all X.400
services
- X.400 user interface definition
These are really coupled. To map the X.400 services, this
specification defines a number of extensions to RFC 822. As a side
effect, these give the 822 user access to SOME X.400 services.
However, the aim on the RFC 822 side is to preserve current service,
and it is intentional that access is not given to all X.400 services.
Thus, it will be a poor choice for X.400 implementors to use RFC
987(88) as an interface - there are too many aspects of X.400 which
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cannot be accessed through it. If a text interface is desired, a
specification targeted at X.400, without RFC 822 restrictions, would
be more appropriate.
1.8. Subsetting
This proposal specifies a mapping which is appropriate to preserve
services in existing RFC 822 communities. Implementations and
specifications which subset this specification are strongly
discouraged.
1.9. Document Structure
This document has five chapters:
1. Overview - this chapter.
2. Service Elements - This describes the (end user) services
mapped by a gateway.
3. Basic mappings - This describes some basic notation used in
Chapters 3-5, the mappings between character sets, and some
fundamental protocol elements.
4. Addressing - This considers the mapping between X.400 O/R
names and RFC 822 addresses, which is a fundamental gateway
component.
5. Detailed Mappings - This describes the details of all other
mappings.
There are also six appendices:
A. Differences with RFC 987
B. Mappings Specific to JNT Mail
C. Mappings Specific to UUCP Mail
D. Object Identifier Assignment
E. BNF Summary
F. Format of Address Tables
WARNING:
THE REMAINDER OF THIS SPECIFICATION IS TECHNICALLY DETAILED.
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IT WILL NOT MAKE SENSE, EXCEPT IN THE CONTEXT OF RFC 822 AND
X.400 (1988). DO NOT ATTEMPT TO READ THIS DOCUMENT UNLESS
YOU ARE FAMILIAR WITH THESE SPECIFICATIONS.
1.10. Acknowledgements
This work was partly sponsored by the Joint Network Team. The
workshop at UCL in June 1989 to work on this specification was also
an IFIP WG 6.5 meeting.
The work in this specification was substantially based on RFC 987,
which had input from many people.
Useful comments and suggestions were made by Pete Cowen (Nottingham
Univ), Jim Craigie (JNT), Christian Huitema (Inria), Peter Lynch
(Prime), Julian Onions (Nottingham Univ), Sandy Shaw (Edinburgh
Univ), Einar Stefferud (NMA), and Peter Sylvester (GMD).
Chapter 2 -- Service Elements
This chapter considers the services offered across a gateway built
according to this specification. It gives a view of the
functionality provided by such a gateway for communication with users
in the opposite domain. This chapter considers service mappings in
the context of SINGLE transfers only, and not repeated mappings
through multiple gateways.
2.1. The Notion of Service Across a Gateway
RFC 822 and X.400 provide a number of services to the end user. This
chapter describes the extent to which each service can be supported
across an X.400 <-> RFC 822 gateway. The cases considered are single
transfers across such a gateway, although the problems of multiple
crossings are noted where appropriate.
2.1.1. Origination of Messages
When a user originates a message, a number of services are available.
Some of these imply actions (e.g., delivery to a recipient), and some
are insertion of known data (e.g., specification of a subject field).
This chapter describes, for each offered service, to what extent it
is supported for a recipient accessed through a gateway. There are
three levels of support:
Supported
The corresponding protocol elements map well, and so the
service can be fully provided.
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Not Supported
The service cannot be provided, as there is a complete
mismatch.
Partial Support
The service can be partially fulfilled.
In the first two cases, the service is simply marked as "Supported"
or "Not Supported". Some explanation may be given if there are
additional implications, or the (non) support is not intuitive. For
partial support, the level of partial support is summarised. Where
partial support is good, this will be described by a phrase such as
"Supported by use of.....". A common case of this is where the
service is mapped onto a non- standard service on the other side of
the gateway, and this would have lead to support if it had been a
standard service. In many cases, this is equivalent to support. For
partial support, an indication of the mechanism is given, in order to
give a feel for the level of support provided. Note that this is not
a replacement for Chapter 5, where the mapping is fully specified.
If a service is described as supported, this implies:
- Semantic correspondence.
- No (significant) loss of information.
- Any actions required by the service element.
An example of a service gaining full support: If an RFC 822
originator specifies a Subject: field, this is considered to be
supported, as an X.400 recipient will get a subject indication.
All RFC 822 services are supported or partially supported for
origination. The implications of non-supported X.400 services is
described under X.400.
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
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RFC 822 service elements.
2.2.1. Origination in RFC 822
A mechanism of mapping, used in several cases, is to map the RFC 822
header into a heading extension in the IPM (InterPersonal Message).
This can be regarded as partial support, as it makes the information
available to any X.400 implementations which are interested in these
services. Communities which require significant RFC 822 interworking
should require that their X.400 User Agents are able to display these
heading extensions. Support for the various service elements
(headers) is now listed.
Date:
Supported.
From:
Supported. For messages where there is also a sender field,
the mapping is to "Authorising Users Indication", which has
subtly different semantics to the general RFC 822 usage of
From:.
Sender:
Supported.
Reply-To:
Supported.
To: Supported.
Cc: Supported.
Bcc: Supported.
Message-Id:
Supported.
In-Reply-To:
Supported, for a single reference. Where multiple
references are given, partial support is given by mapping to
"Cross Referencing Indication". This gives similar
semantics.
References:
Supported.
Keywords:
Supported by use of a heading extension.
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Subject:
Supported.
Comments:
Supported by use of an extra body part.
Encrypted:
Supported by use of a heading extension.
Resent-*
Supported by use of a heading extension. Note that
addresses in these fields are mapped onto text, and so are
not accessible to the X.400 user as addresses. In
principle, fuller support would be possible by mapping onto
a forwarded IP Message, but this is not suggested.
Other Fields
In particular X-* fields, and "illegal" fields in common
usage (e.g., "Fruit-of-the-day:") are supported by use of
heading extensions.
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:
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Subject:
The following non-standard services (headers) may be present. These
are defined in more detail in Chapter 5 (5.3.4, 5.3.6, 5.3.7):
Autoforwarded:
Content-Identifier:
Conversion:
Conversion-With-Loss:
Delivery-Date:
Discarded-X400-IPMS-Extensions:
Discarded-X400-MTS-Extensions:
DL-Expansion-History:
Deferred-Delivery:
Expiry-Date:
Importance:
Incomplete-Copy:
Language:
Latest-Delivery-Time:
Message-Type:
Obsoletes:
Original-Encoded-Information-Types:
Originator-Return-Address:
Priority:
Redirection-History:
Reply-By:
Requested-Delivery-Method:
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Sensitivity:
X400-Content-Type:
X400-MTS-Identifier:
X400-Originator:
X400-Received:
X400-Recipients:
2.3. X.400
2.3.1. Origination in X.400
When mapping services from X.400 to RFC 822 which are not supported
by RFC 822, new RFC 822 headers are defined. It is intended that
these fields will be registered, and that co-operating RFC 822
systems may use them. Where these new fields are used, and no system
action is implied, the service can be regarded as being partially
supported. Chapter 5 describes how to map X.400 services onto these
new headers. Other elements are provided, in part, by the gateway as
they cannot be provided by RFC 822.
Some service elements are marked N/A (not applicable). There are
five cases, which are marked with different comments:
N/A (local)
These elements are only applicable to User Agent / Message
Transfer Agent interaction and so they cannot apply to RFC
822 recipients.
N/A (PDAU)
These service elements are only applicable where the
recipient is reached by use of a Physical Delivery Access
Unit (PDAU), and so do not need to be mapped by the gateway.
N/A (reception)
These services are only applicable for reception.
N/A (prior)
If requested, this service must be performed prior to the
gateway.
N/A (MS)
These services are only applicable to Message Store (i.e., a
local service).
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Finally, some service elements are not supported. In particular, the
new security services are not mapped onto RFC 822. Unless otherwise
indicated, the behaviour of service elements marked as not supported
will depend on the criticality marking supplied by the user. If the
element is marked as critical for transfer or delivery, a non-
delivery notification will be generated. Otherwise, the service
request will be ignored.
2.3.1.1. Basic Interpersonal Messaging Service
These are the mandatory IPM services as listed in Section 19.8 of
X.400 / ISO/IEC 10021-1, listed here in the order given. Section
19.8 has cross references to short definitions of each service.
Access management
N/A (local).
Content Type Indication
Supported by a new RFC 822 header (Content-Type:).
Converted Indication
Supported by a new RFC 822 header (X400-Received:).
Delivery Time Stamp Indication
N/A (reception).
IP Message Identification
Supported.
Message Identification
Supported, by use of a new RFC 822 header
(X400-MTS-Identifier). This new header is required, as
X.400 has two message-ids whereas RFC 822 has only one (see
previous service).
Non-delivery Notification
Not supported, although in general an RFC 822 system will
return error reports by use of IP messages. In other
service elements, this pragmatic result can be treated as
effective support of this service element.
Original Encoded Information Types Indication
Supported as a new RFC 822 header
(Original-Encoded-Information-Types:).
Submission Time Stamp Indication
Supported.
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Typed Body
Some types supported. IA5 is fully supported.
ForwardedIPMessage is supported, with some loss of
information. Other types get some measure of support,
dependent on X.400 facilities for conversion to IA5. This
will only be done where content conversion is not
prohibited.
User Capabilities Registration
N/A (local).
2.3.1.2. IPM Service Optional User Facilities
This section describes support for the optional (user selectable) IPM
services as listed in Section 19.9 of X.400 / ISO/IEC 10021- 1,
listed here in the order given. Section 19.9 has cross references to
short definitions of each service.
Additional Physical Rendition
N/A (PDAU).
Alternate Recipient Allowed
Not supported. There is no RFC 822 service equivalent to
prohibition of alternate recipient assignment (e.g., an RFC
822 system may freely send an undeliverable message to a
local postmaster). Thus, the gateway cannot prevent
assignment of alternative recipients on the RFC 822 side.
This service really means giving the user control as to
whether or not an alternate recipient is allowed. This
specification requires transfer of messages to RFC 822
irrespective of this service request, and so this service is
not supported.
Authorising User's Indication
Supported.
Auto-forwarded Indication
Supported as new RFC 822 header (Auto-Forwarded:).
Basic Physical Rendition
N/A (PDAU).
Blind Copy Recipient Indication
Supported.
Body Part Encryption Indication
Supported by use of a new RFC 822 header
(Original-Encoded-Information-Types:), although in most
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cases it will not be possible to map the body part in
question.
Content Confidentiality
Not supported.
Content Integrity
Not supported.
Conversion Prohibition
Supported. In this case, only messages with IA5 body parts,
other body parts which contain only IA5, and Forwarded IP
Messages (subject recursively to the same restrictions),
will be mapped.
Conversion Prohibition in Case of Loss of Information
Supported.
Counter Collection
N/A (PDAU).
Counter Collection with Advice
N/A (PDAU).
Cross Referencing Indication
Supported.
Deferred Delivery
N/A (prior). This service should always be provided by the
MTS prior to the gateway. A new RFC 822 header
(Deferred-Delivery:) is provided to transfer information on
this service to the recipient.
Deferred Delivery Cancellation
N/A (local).
Delivery Notification
Supported. This is performed at the gateway. Thus, a
notification is sent by the gateway to the originator. If
the 822-MTS protocol is JNT Mail, a notification may also be
sent by the recipient UA.
Delivery via Bureaufax Service
N/A (PDAU).
Designation of Recipient by Directory Name
N/A (local).
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RFC 1138 Mapping X.400(88) and 822 December 1989
Disclosure of Other Recipients
Supported by use of a new RFC 822 header (X400-Recipients:).
This is descriptive information for the RFC 822 recipient,
and is not reverse mappable.
DL Expansion History Indication
Supported by use of a new RFC 822 header
(DL-Expansion-History:).
DL Expansion Prohibited
Distribution List means MTS supported distribution list, in
the manner of X.400. This service does not exist in the RFC
822 world. RFC 822 distribution lists should be regarded as
an informal redistribution mechanism, beyond the scope of
this control. Messages will be sent to RFC 822,
irrespective of whether this service is requested.
Theoretically therefore, this service is supported, although
in practice it may appear that it is not supported.
Express Mail Service
N/A (PDAU).
Expiry Date Indication
Supported as new RFC 822 header (Expiry-Date:). In general,
no automatic action can be expected.
Explicit Conversion
N/A (prior).
Forwarded IP Message Indication
Supported, with some loss of information. The message is
forwarded in an RFC 822 body, and so can only be interpreted
visually.
Grade of Delivery Selection
N/A (PDAU)
Importance Indication
Supported as new RFC 822 header (Importance:).
Incomplete Copy Indication
Supported as new RFC 822 header (Incomplete-Copy:).
Language Indication
Supported as new RFC 822 header (Language:).
Latest Delivery Designation
Not supported. A new RFC 822 header (Latest-Delivery-Time:)
Kille [Page 19]
RFC 1138 Mapping X.400(88) and 822 December 1989
is provided, which may be used by the recipient.
Message Flow Confidentiality
Not supported.
Message Origin Authentication
N/A (reception).
Message Security Labelling
Not supported.
Message Sequence Integrity
Not supported.
Multi-Destination Delivery
Supported.
Multi-part Body
Supported, with some loss of information, in that the
structuring cannot be formalised in RFC 822.
Non Receipt Notification Request
Not supported.
Non Repudiation of Delivery
Not supported.
Non Repudiation of Origin
N/A (reception).
Non Repudiation of Submission
N/A (local).
Obsoleting Indication
Supported as new RFC 822 header (Obsoletes:).
Ordinary Mail
N/A (PDAU).
Originator Indication
Supported.
Originator Requested Alternate Recipient
Not supported, but is placed as comment next to address
(X400-Recipients:).
Physical Delivery Notification by MHS
N/A (PDAU).
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RFC 1138 Mapping X.400(88) and 822 December 1989
Physical Delivery Notification by PDS
N/A (PDAU).
Physical Forwarding Allowed
Supported by use of a comment in a new RFC 822 header
(X400-Recipients:), associated with the recipient in
question.
Physical Forwarding Prohibited
Supported by use of a comment in a new RFC 822 header
(X400-Recipients:), associated with the recipient in
question.
Prevention of Non-delivery notification
Supported, as delivery notifications cannot be generated by
RFC 822. In practice, errors will be returned as IP
Messages, and so this service may appear not to be supported
(see Non-delivery Notification).
Primary and Copy Recipients Indication
Supported.
Probe
Supported at the gateway (i.e., the gateway services the
probe).
Probe Origin Authentication
N/A (reception).
Proof of Delivery
Not supported.
Proof of Submission
N/A (local).
Receipt Notification Request Indication
Not supported.
Redirection Allowed by Originator
Redirection means MTS supported redirection, in the manner
of X.400. This service does not exist in the RFC 822 world.
RFC 822 redirection (e.g., aliasing) should be regarded as
an informal redirection mechanism, beyond the scope of this
control. Messages will be sent to RFC 822, irrespective of
whether this service is requested. Theoretically therefore,
this service is supported, although in practice it may
appear that it is not supported.
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RFC 1138 Mapping X.400(88) and 822 December 1989
Registered Mail
N/A (PDAU).
Registered Mail to Addressee in Person
N/A (PDAU).
Reply Request Indication
Supported as comment next to address.
Replying IP Message Indication
Supported.
Report Origin Authentication
N/A (reception).
Request for Forwarding Address
N/A (PDAU).
Requested Delivery Method
N/A (local). The services required must be dealt with at
submission time. Any such request is made available through
the gateway by use of a comment associated with the
recipient in question.
Return of Content
In principle, this is N/A, as non-delivery notifications are
not supported. In practice, most RFC 822 systems will
return part or all of the content along with the IP Message
indicating an error (see Non-delivery Notification).
Sensitivity Indication
Supported as new RFC 822 header (Sensitivity:).
Special Delivery
N/A (PDAU).
Stored Message Deletion
N/A (MS).
Stored Message Fetching
N/A (MS).
Stored Message Listing
N/A (MS).
Stored Message Summary
N/A (MS).
Kille [Page 22]
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Subject Indication
Supported.
Undeliverable Mail with Return of Physical Message
N/A (PDAU).
Use of Distribution List
In principle this applies only to X.400 supported
distribution lists (see DL Expansion Prohibited).
Theoretically, this service is N/A (prior). In practice,
because of informal RFC 822 lists, this service can be
regarded as supported.
2.3.2. Reception by X.400
2.3.2.1. Standard Mandatory Services
The following standard IPM mandatory user facilities may be required
for reception of RFC 822 originated mail by an X.400 UA.
Content Type Indication
Delivery Time Stamp Indication
IP Message Identification
Message Identification
Non-delivery Notification
Original Encoded Information Types Indication
Submission Time Stamp Indication
Typed Body
2.3.2.2. Standard Optional Services
The following standard IPM optional user facilities may be required
for reception of RFC 822 originated mail by an X.400 UA.
Authorising User's Indication
Blind Copy Recipient Indication
Cross Referencing Indication
Originator Indication
Kille [Page 23]
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Primary and Copy Recipients Indication
Replying IP Message Indication
Subject Indication
2.3.2.3. New Services
A new service "RFC 822 Header Field" is defined using the extension
facilities. This allows for any RFC 822 header field to be
represented. It may be present in RFC 822 originated messages, which
are received by an X.400 UA.
Chapter 3 -- Basic Mappings
3.1. Notation
The X.400 protocols are encoded in a structured manner according to
ASN.1, whereas RFC 822 is text encoded. To define a detailed
mapping, it is necessary to refer to detailed protocol elements in
each format. A notation to achieve this is described in this
section.
3.1.1. RFC 822
Structured text is defined according to the Extended Backus Naur Form
(EBNF) defined in Section 2 of RFC 822 [Crocker82a]. In the EBNF
definitions used in this specification, the syntax rules given in
Appendix D of RFC 822 are assumed. When these EBNF tokens are
referred to outside an EBNF definition, they are identified by the
string "822." appended to the beginning of the string (e.g.,
822.addr-spec). Additional syntax rules, to be used throughout this
specification, are defined in this chapter.
The EBNF is used in two ways.
1. To describe components of RFC 822 messages (or of 822-MTS
components). In this case, the lexical analysis defined in
Section 3 of RFC 822 should be used. When these new EBNF
tokens are referred to outside an EBNF definition, they are
identified by the string "EBNF." appended to the beginning
of the string (e.g., EBNF.bilateral-info).
2. To describe the structure of IA5 or ASCII information not in
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.
Kille [Page 24]
RFC 1138 Mapping X.400(88) and 822 December 1989
3.1.2. ASN.1
An element is referred to with the following syntax, defined in EBNF:
element = service "." definition *( "." definition )
service = "IPMS" / "MTS" / "MTA"
definition = identifier / context
identifier = ALPHA *< ALPHA or DIGIT or "-" >
context = "[" 1*DIGIT "]"
The EBNF.service keys are shorthand for the following service
specifications:
IPMS IPMSInformationObjects defined in Annex E of X.420 / ISO
10021-7.
MTS MTSAbstractService defined in Section 9 of X.411 / ISO
10021-4.
MTA MTAAbstractService defined in Section 13 of X.411 / ISO
10021-4.
The first EBNF.identifier identifies a type or value key in the
context of the defined service specification. Subsequent
EBNF.identifiers identify a value label or type in the context of the
first identifier (SET or SEQUENCE). EBNF.context indicates a context
tag, and is used where there is no label or type to uniquely identify
a component. The special EBNF.identifier keyword "value" is used to
denote an element of a sequence.
For example, IPMS.Heading.subject defines the subject element of the
IPMS heading. The same syntax is also used to refer to element
values. For example, MTS.EncodedInformationTypes.[0].g3Fax refers to
a value of MTS.EncodedInformationTypes.[0].
3.2. ASCII and IA5
A gateway will interpret all IA5 as ASCII. Thus, mapping between
these forms is conceptual.
3.3. Standard Types
There is a need to convert between ASCII text, and some of the types
defined in ASN.1 [CCITT/ISO88d]. For each case, an EBNF syntax
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
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RFC 1138 Mapping X.400(88) and 822 December 1989
ASN.1 types are referred to with the first letter in upper case.
Except as noted, all mappings are symmetrical.
3.3.1. Boolean
Boolean is encoded as:
boolean = "TRUE" / "FALSE"
3.3.2. NumericString
NumericString is encoded as:
numericstring = *DIGIT
3.3.3. PrintableString
PrintableString is a restricted IA5String defined as:
printablestring = *( ps-char )
ps-restricted-char = 1DIGIT / 1ALPHA / " " / "'" / "+"
/ "," / "-" / "." / "/" / ":" / "=" / "?"
ps-delim = "(" / ")"
ps-char = ps-delim / ps-restricted-char
This can be used to represent real printable strings in EBNF.
3.3.4. T.61String
In cases where T.61 strings are only used for conveying human
interpreted information, the aim of a mapping should be to render the
characters appropriately in the remote character set, rather than to
maximise reversibility. For these cases, the mappings to IA5 defined
in CCITT Recommendation X.408 (1988) should be used [CCITT/ISO88a].
These will then be encoded in ASCII.
There is also a need to represent Teletex Strings in ASCII, for some
aspects of O/R Address. For these, the following encoding is used:
teletex-string = *( ps-char / t61-encoded )
t61-encoded = "{" 1* t61-encoded-char "}"
t61-encoded-char = 3DIGIT
Common characters are mapped simply. Other octets are mapped using a
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
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RFC 1138 Mapping X.400(88) and 822 December 1989
Printable String representation. The following BNF is used to
represent this.
teletex-and-or-ps = [ printablestring ] [ "*" teletex-string ]
The natural mapping is restricted to EBNF.ps-char, in order to make
the full BNF easier to parse.
3.3.5. UTCTime
Both UTCTime and the RFC 822 822.date-time syntax contain: Year
(lowest two digits), Month, Day of Month, hour, minute, second
(optional), and Timezone. 822.date-time also contains an optional
day of the week, but this is redundant. Therefore a symmetrical
mapping can be made between these constructs.
Note:
In practice, a gateway will need to parse various illegal
variants on 822.date-time. In cases where 822.date-time
cannot be parsed, it is recommended that the derived UTCTime
is set to the value at the time of translation.
The UTCTime format which specifies the timezone offset should be
used.
3.3.6. Integer
A basic ASN.1 Integer will be mapped onto EBNF.numericstring. In many
cases ASN.1 will enumerate Integer values or use ENUMERATED. An EBNF
encoding labelled-integer is provided. When mapping from EBNF to
ASN.1, only the integer value is mapped, and the associated text is
discarded. When mapping from ASN.1 to EBNF, addition of an
appropriate text label is strongly encouraged.
labelled-integer ::= [ key-string ] "(" numericstring ")"
key-string = *key-char
key-char = <a-z, A-Z, 1-9, and "-">
3.3.7. Object Identifier
Object identifiers are represented in a form similar to that
given in ASN.1. The numbers are mandatory, to ease encoding.
It is recommended that as many strings as possible are used, to
facilitate user recognition.
object-identifier ::= [ defined-value ] oid-comp-list
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RFC 1138 Mapping X.400(88) and 822 December 1989
oid-comp-list ::= oid-comp oid-comp-list
| oid-comp
defined-value ::= key-string
oid-comp ::= [ key-string ] "(" numericstring ")"
3.4. Encoding ASCII in Printable String
Some information in RFC 822 is represented in ASCII, and needs to be
mapped into X.400 elements encoded as printable string. For this
reason, a mechanism to represent ASCII encoded as PrintableString is
needed.
A structured subset of EBNF.printablestring is now defined. This can
be used to encode ASCII in the PrintableString character set.
ps-encoded = *( ps-restricted-char / ps-encoded-char )
ps-encoded-char = "(a)" ; (@)
/ "(p)" ; (%)
/ "(b)" ; (!)
/ "(q)" ; (")
/ "(u)" ; (_)
/ "(l)" ; "("
/ "(r)" ; ")"
/ "(" 3DIGIT ")"
The 822.3DIGIT in EBNF.ps-encoded-char must have range 0-127, and is
interpreted in decimal as the corresponding ASCII character. Special
encodings are given for: at sign (@), percent (%), exclamation
mark/bang (!), double quote ("), underscore (_), left bracket ((),
and right bracket ()). These characters, with the exception of round
brackets, are not included in PrintableString, but are common in RFC
822 addresses. The abbreviations will ease specification of RFC 822
addresses from an X.400 system. These special encodings should be
mapped in a case insensitive manner, but always be generated in lower
case.
A reversible mapping between PrintableString and ASCII can now be
defined. The reversibility means that some values of printable
string (containing round braces) cannot be generated from ASCII.
Therefore, this mapping must only be used in cases where the
printable strings may only be derived from ASCII (and will therefore
have a restricted domain). For example, in this specification, it is
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.
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To encode ASCII as PrintableString, the EBNF.ps-encoded syntax is
used, with all EBNF.ps-restricted-char mapped directly. All other
822.CHAR are encoded as EBNF.ps-encoded-char.
To encode PrintableString as ASCII, parse PrintableString as
EBNF.ps-encoded, and then reverse the previous mapping. If the
PrintableString cannot be parsed, then the mapping is being applied
in to an inappropriate value, and an error should be given to the
procedure doing the mapping. In some cases, it may be preferable to
pass the printable string through unaltered.
Some examples are now given. Note the arrows which indicate
asymmetrical mappings:
PrintableString ASCII
'a demo.' <-> 'a demo.'
foo(a)bar <-> foo@bar
(q)(u)(p)(q) <-> "_%"
(a) <-> @
(A) <-> @
(l)a(r) <-> (a)
(126) <-> ~
( -> (
(l) <-> (
Chapter 4 -- Addressing
Addressing is probably the trickiest problem of an X.400 <-> RFC 822
gateway. Therefore it is given a separate chapter. This chapter, as
a side effect, also defines a textual representation of an X.400 O/R
Address.
Initially, we consider an address in the (human) mail user sense of
"what is typed at the mailsystem to reference a mail user". A basic
RFC 822 address is defined by the EBNF EBNF.822-address:
822-address = [ route ] addr-spec
In an 822-MTS protocol, the originator and each recipient should be
considered to be defined by such a construct. In an RFC 822 header,
the EBNF.822-address is encapsulated in the 822.address syntax rule,
and there may also be associated comments. None of this extra
information has any semantics, other than to the end user.
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
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IPMS.ORDescriptor.
It can be seen that RFC 822 822.address must be mapped with
IPMS.ORDescriptor, and that RFC 822 EBNF.822-address must be mapped
with MTS.ORAddress.
4.1. A textual representation of MTS.ORAddress
MTS.ORAddress is structured as a set of attribute value pairs. It is
clearly necessary to be able to encode this in ASCII for gatewaying
purposes. All aspects should be encoded, in order to guarantee
return of error messages, and to optimise third party replies.
4.2. Basic Representation
An O/R Address has a number of structured and unstructured
attributes. For each unstructured attribute, a key and an encoding
is specified. For structured attributes, the X.400 attribute is
mapped onto one or more attribute value pairs. For domain defined
attributes, each element of the sequence will be mapped onto a triple
(key and two values), with each value having the same encoding. The
attributes are as follows, with 1984 attributes given in the first
part of the table. For each attribute, a reference is given,
consisting of the relevant sections in X.402 / ISO 10021-2, and the
extension identifier for 88 only attributes:
Attribute (Component) Key Enc Ref Id
84/88 Attributes
MTS.CountryName C P 18.3.3
MTS.AdministrationDomainName ADMD P 18.3.1
MTS.PrivateDomainName PRMD P 18.3.21
MTS.NetworkAddress X121 N 18.3.7
MTS.TerminalIdentifier T-ID N 18.3.23
MTS.OrganizationName O P/T 18.3.9
MTS.OrganizationalUnitNames.value OU P/T 18.3.10
MTS.NumericUserIdentifier UA-ID N 18.3.8
MTS.PersonalName PN P/T 18.3.12
MTS.PersonalName.surname S P/T 18.3.12
MTS.PersonalName.given-name G P/T 18.3.12
MTS.PersonalName.initials I P/T 18.3.12
MTS.PersonalName
.generation-qualifier GQ P/T 18.3.12
MTS.DomainDefinedAttribute.value DD P/T 18.1
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88 Attributes
MTS.CommonName CN P/T 18.3.2 1
MTS.TeletexCommonName CN P/T 18.3.2 2
MTS.TeletexOrganizationName O P/T 18.3.9 3
MTS.TeletexPersonalName PN P/T 18.3.12 4
MTS.TeletexPersonalName.surname S P/T 18.3.12 4
MTS.TeletexPersonalName.given-name G P/T 18.3.12 4
MTS.TeletexPersonalName.initials I P/T 18.3.12 4
MTS.TeletexPersonalName
.generation-qualifier GQ P/T 18.3.12 4
MTS.TeletexOrganizationalUnitNames
.value OU P/T 18.3.10 5
MTS.TeletexDomainDefinedAttribute
.value DD P/T 18.1 6
MTS.PDSName PD-SYSTEM P 18.3.11 7
MTS.PhysicalDeliveryCountryName PD-C P 18.3.13 8
MTS.PostalCode POSTCODE P 18.3.19 9
MTS.PhysicalDeliveryOfficeName PD-OFFICE P/T 18.3.14 10
MTS.PhysicalDeliveryOfficeNumber PD-OFFICE-NUM P/T 18.3.15 11
MTS.ExtensionORAddressComponents PD-EXT-D P/T 18.3.4 12
MTS.PhysicalDeliveryPersonName PD-PN P/T 18.3.17 13
MTS.PhysicalDelivery PD-O P/T 18.3.16 14
OrganizationName
MTS.ExtensionPhysicalDelivery
AddressComponents PD-EXT-LOC P/T 18.3.5 15
MTS.UnformattedPostalAddress PD-ADDRESS P/T 18.3.25 16
MTS.StreetAddress STREET P/T 18.3.22 17
MTS.PostOfficeBoxAddress PO-BOX P/T 18.3.18 18
MTS.PosteRestanteAddress POSTE-RESTANTE P/T 18.3.20 19
MTS.UniquePostalName PD-UNIQUE P/T 18.3.26 20
MTS.LocalPostalAttributes PD-LOCAL P/T 18.3.6 21
MTS.ExtendedNetworkAddress
.e163-4-address.number NET-NUM N 18.3.7 22
MTS.ExtendedNetworkAddress
.e163-4-address.sub-address NET-SUB N 18.3.7 22
MTS.ExtendedNetworkAddress
.psap-address NET-PSAP X 18.3.7 22
MTS.TerminalType NET-TTYPE I 18.3.24 23
The following keys identify different EBNF encodings, which are
associated with the ASCII representation of MTS.ORAddress.
Key Encoding
P printablestring
N numericstring
T teletex-string
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P/T teletex-and-or-ps
I labelled-integer
X presentation-address
The BNF for presentation-address is taken from the specification "A
String Encoding of Presentation Address" [Kille89a].
In most cases, the EBNF encoding maps directly to the ASN.1 encoding
of the attribute. There are a few exceptions. In cases where an
attribute can be encoded as either a PrintableString or NumericString
(Country, ADMD, PRMD), either form should be mapped into the BNF.
When generating ASN.1, the NumericString encoding should be used if
the string contains only digits.
There are a number of cases where the P/T (teletex-and-or-ps)
representation is used. Where the key maps to a single attribute,
this choice is reflected in the encoding of the attribute (attributes
10-21). For most of the 1984 attributes and common name, there is a
printablestring and a teletex variant. This pair of attributes is
mapped onto the single component here. This will give a clean
mapping for the common cases where only one form of the name is used.
4.2.1. Encoding of Personal Name
Handling of Personal Name and Teletex Personal Name based purely on
the EBNF.standard-type syntax defined above is likely to be clumsy.
It seems desirable to utilise the "human" conventions for encoding
these components. A syntax is defined, which is designed to provide
a clean encoding for the common cases of O/R address specification
where:
1. There is no generational qualifier
2. Initials contain only letters
3. Given Name does not contain full stop ("."), and is at least
two characters long.
4. If Surname contains full stop, then it may not be in the
first two characters, and either initials or given name is
present.
The following EBNF is defined:
encoded-pn = [ given "." ] *( initial "." ) surname
given = 2*<ps-char not including ".">
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initial = ALPHA
surname = printablestring
This can be used to map from any string containing only printable
string characters to an O/R address personal name. Parse the string
according to the EBNF. The given name and surname are assigned
directly. All EBNF.initial tokens are concatenated without
intervening full stops to generate the initials.
For an O/R address which follows the above restrictions, a string can
be derived in the natural manner. In this case, the mapping will be
reversible.
For example:
GivenName = "Marshall"
Surname = "Rose"
Maps with "Marshall.Rose"
Initials = "MT"
Surname = "Rose"
Maps with "M.T.Rose"
GivenName = "Marshall"
Initials = "MT"
Surname = "Rose"
Maps with "Marshall.M.T.Rose"
Note that X.400 suggest that Initials is used to encode ALL initials.
Therefore, the proposed encoding is "natural" when either GivenName
or Initials, but not both, are present. The case where both are
present can be encoded, but this appears to be contrived!
4.2.2. Standard Encoding of MTS.ORAddress
Given this structure, we can specify a BNF representation of an O/R
Address.
std-or-address = 1*( "/" attribute "=" value ) "/"
attribute = standard-type
/ "RFC-822"
/ registered-dd-type
/ dd-key "." std-printablestring
standard-type = key-string
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RFC 1138 Mapping X.400(88) and 822 December 1989
registered-dd-type
= key-string
dd-key = key-string
value = std-printablestring
std-printablestring
= *( std-char / std-pair )
std-char = <"{", "}", "*", and any ps-char
except "/" and "=">
std-pair = "$" ps-char
The standard-type is any key defined in the table in Section 4.2,
except PN, and DD. The value, after quote removal, should be
interpreted according to the defined encoding.
If the standard-type is PN, the value is interpreted according to
EBNF.encoded-pn, and the components of MTS.PersonalName and/or
MTS.TeletexPersonalName derived accordingly.
If dd-key is the recognised Domain Defined string (DD), then the type
and value should be interpreted according to the syntax implied from
the encoding, and aligned to either the teletex or printable string
form. Key and value should have the same encoding.
If value is "RFC-822", then the (printable string) Domain Defined
Type of "RFC-822" is assumed. This is an optimised encoding of the
domain defined type defined by this specification.
The matching of all keywords should be done in a case- independent
manner.
If the value is registered-dd-type, the value is registered with the
IANA and will be listed in the Assigned Numbers RFC, then the value
should be interpreted accordingly. This restriction maximises the
syntax checking which can be done at a gateway.
4.3. EBNF.822-address <-> MTS.ORAddress
Ideally, the mapping specified would be entirely symmetrical and
global, to enable addresses to be referred to transparently in the
remote system, with the choice of gateway being left to the Message
Transfer Service. There are two fundamental reasons why this is not
possible:
1. The syntaxes are sufficiently different to make this
awkward.
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RFC 1138 Mapping X.400(88) and 822 December 1989
2. In the general case, there would not be the necessary
administrative co-operation between the X.400 and RFC 822
worlds, which would be needed for this to work.
Therefore, an asymmetrical mapping is defined, which can be
symmetrical where there is appropriate administrative control.
4.3.1. X.400 encoded in RFC 822
The std-or-address syntax is used to encode O/R Address information
in the 822.local-part of EBNF.822-address. Further O/R Address
information may be associated with the 822.domain component. This
cannot be used in the general case, basically due to character set
problems, and lack of order in X.400 O/R Addresses. The only way to
encode the full PrintableString character set in a domain is by use
of the 822.domain-ref syntax (i.e., 822.atom). This is likely to
cause problems on many systems. The effective character set of
domains is in practice reduced from the RFC 822 set, by restrictions
imposed by domain conventions and policy.
A generic 822.address consists of a 822.local-part and a sequence of
822.domains (e.g., <@domain1,@domain2:user@domain3>). All except the
822.domain associated with the 822.local-part (domain3 in this case)
should be considered to specify routing within the RFC 822 world, and
will not be interpreted by the gateway (although they may have
identified the gateway from within the RFC 822 world).
This form of source routing is now discouraged in the Internet
(Host Requirements, page 58 [Braden89a]).
The 822.domain associated with the 822.local-part may also identify
the gateway from within the RFC 822 world. This final 822.domain may
be used to determine some number of O/R Address attributes. The
following O/R Address attributes are considered as a hierarchy, and
may be specified by the domain. They are (in order of hierarchy):
Country, ADMD, PRMD, Organisation, Organisational Unit
There may be multiple Organisational Units.
Associations may be defined between domain specifications, and
some set of attributes. This association proceeds hierarchically.
For example, if a domain implies ADMD, it also implies country.
Subdomains under this are associated according to the O/R Address
hierarchy. For example:
=> "AC.UK" might be associated with
C="GB", ADMD="GOLD 400", PRMD="UK.AC"
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then domain "R-D.Salford.AC.UK" maps with
C="GB", ADMD="GOLD 400", PRMD="UK.AC", O="Salford", OU="R-D"
There are three basic reasons why a domain/attribute mapping might
be maintained, as opposed to using simply subdomains:
1. As a shorthand to avoid redundant X.400 information. In
particular, there will often be only one ADMD per country,
and so it does not need to be given explicitly.
2. To deal with cases where attribute values do not fit the
syntax:
domain-syntax = alphanum [ *alphanumhyphen alphanum ]
alphanum = <ALPHA or DIGIT>
alphanumhyphen = <ALPHA or DIGIT or HYPHEN>
Although RFC 822 allows for a more general syntax, this
restricted syntax is chosen as it is the one chosen by the
various domain service administrations.
3. To deal with missing elements in the hierarchy. A domain
may be associated with an omitted attribute in conjunction
with several present ones. When performing the algorithmic
insertion of components lower in the hierarchy, the omitted
value should be skipped. For example, if "HNE.EGM" is
associated with "C=TC", "ADMD=ECQ", "PRMD=HNE", and omitted
organisation, then "ZI.HNE.EGM" is mapped with "C=TC",
"ADMD=ECQ", "PRMD=HNE", "OU=ZI". It should be noted that
attributes may have null values, and that this is treated
separately from omitted attributes (whilst it would be bad
practice to treat these two cases differently, they must be
allowed for).
This set of mappings need only be known by the gateways relaying
between the RFC 822 world, and the O/R Address space associated with
the mapping in question. However, it is desirable (for the optimal
mapping of third party addresses) for all gateways to know these
mappings. A format for the exchange of this information is defined
in Appendix F.
The remaining attributes are encoded on the LHS, using the EBNF.std-
or-address syntax. For example:
/I=J/S=Linnimouth/GQ=5/@Marketing.Widget.COM
encodes the MTS.ORAddress consisting of:
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MTS.CountryName = "TC"
MTS.AdministrationDomainName = "BTT"
MTS.OrganizationName = "Widget"
MTS.OrganizationalUnitNames.value = "Marketing"
MTS.PersonalName.surname = "Linnimouth"
MTS.PersonalName.initials = "J"
MTS.PersonalName.generation-qualifier = "5"
The first three attributes are determined by the domain Widget.COM.
Then, the first element of OrganizationalUnitNames is determined
systematically, and the remaining attributes are encoded on the LHS.
In an extreme case, all of the attributes will be on the LHS. As the
domain cannot be null, the RHS will simply be a domain indicating the
gateway.
The RHS (domain) encoding is designed to deal cleanly with common
addresses, and so the amount of information on the RHS should be
maximised. In particular, it covers the Mnemonic O/R Address using a
1984 compatible encoding. This is seen as the dominant form of O/R
Address. Use of other forms of O/R Address, and teletex encoded
attributes will require an LHS encoding.
There is a further mechanism to simplify the encoding of common
cases, where the only attributes to be encoded on the LHS is a (non-
Teletex) Personal Name attributes which comply with the restrictions
of 4.2.1. To achieve this, the 822.local-part shall be encoded as
EBNF.encoded-pn. In the previous example, if the GenerationQualifier
was not present, the encoding J.Linnimouth@Marketing.Widget.COM would
result.
From the standpoint of the RFC 822 Message Transfer System, the
domain specification is simply used to route the message in the
standard manner. The standard domain mechanisms are are used to
select appropriate gateways for the corresponding O/R Address space.
In most cases, this will be done by registering the higher levels,
and assuming that the gateway can handle the lower levels.
4.3.2. RFC 822 encoded in X.400
In some cases, the encoding defined above may be reversed, to give a
"natural" encoding of genuine RFC 822 addresses. This depends
largely on the allocation of appropriate management domains.
The general case is mapped by use of domain defined attributes. A
Domain defined type "RFC-822" is defined. The associated attribute
value is an ASCII string encoded according to Section 3.3.3 of this
specification. The interpretation of the ASCII string depends on the
context of the gateway.
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RFC 1138 Mapping X.400(88) and 822 December 1989
1. In the context of RFC 822, and RFC 1034
[Crocker82a, Mockapetris87a], the string can be used
directly.
2. In the context of the JNT Mail protocol, and the NRS
[Kille84a, Larmouth83a], the string should be interpreted
according to Mailgroup Note 15 [Kille84b].
3. In the context of UUCP based systems, the string should be
interpreted as defined in [Horton86a].
Other O/R Address attributes will be used to identify a context in
which the O/R Address will be interpreted. This might be a
Management Domain, or some part of a Management Domain which
identifies a gateway MTA. For example:
C = "GB"
ADMD = "GOLD 400"
PRMD = "UK.AC"
O = "UCL"
OU = "CS"
"RFC-822" = "Jimmy(a)WIDGET-LABS.CO.UK"
OR
C = "TC"
ADMD = "Wizz.mail"
PRMD = "42"
"rfc-822" = "Postel(a)venera.isi.edu"
Note in each case the PrintableString encoding of "@" as "(a)". In
the second example, the "RFC-822" domain defined attribute is
interpreted everywhere within the (Private) Management Domain. In
the first example, further attributes are needed within the
Management Domain to identify a gateway. Thus, this scheme can be
used with varying levels of Management Domain co-operation.
4.3.3. Component Ordering
In most cases, ordering of O/R Address components is not significant
for the mappings specified. However, Organisational Units (printable
string and teletex forms) and Domain Defined Attributes are specified
as SEQUENCE in MTS.ORAddress, and so their order may be significant.
This specification needs to take account of this:
1. To allow consistent mapping into the domain hierarchy
2. To ensure preservation of order over multiple mappings.
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There are three places where an order must be specified:
1. The text encoding (std-or-address) of MTS.ORAddress as used
in the local-part of an RFC 822 address. An order is needed
for those components which may have multiple values
(Organisational Unit, and Domain Defined Attributes). When
generating an 822.std-or-address, components of a given type
shall be in hierarchical order with the most significant
component on the RHS. If there is an Organisation
Attribute, it shall be to the right of any Organisational
Unit attributes. These requirements are for the following
reasons:
- Alignment to the hierarchy of other components in RFC
822 addresses (thus, Organisational Units will appear
in the same order, whether encoded on the RHS or LHS).
Note the differences of JNT Mail as described in
Appendix B.
- Backwards compatibility with RFC 987/1026.
- To ensure that gateways generate consistent addresses.
This is both to help end users, and to generate
identical message ids.
Further, it is recommended that all other attributes are
generated according to this ordering, so that all attributes
so encoded follow a consistent hierarchy.
There will be some cases where an X.400 O/R address of this
encoding will be generated by an end user from external
information. The ordering of attributes may be inverted or
mixed. For this reason, the following heuristics may be
applied:
- If there is an Organisation attribute to the left of
any Org Unit attribute, assume that the hierarchy is
inverted.
- If an inversion of the Org Unit hierarchy generates a
valid address, when the preferred order does not,
assume that the hierarchy is inverted.
2. For the Organisational Units (OU) in MTS.ORAddress, the
first OU in the SEQUENCE is the most significant, as
specified in X.400.
3. For the Domain Defined Attributes in MTS.ORAddress, the
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RFC 1138 Mapping X.400(88) and 822 December 1989
First Domain Defined Attribute in the SEQUENCE is the most
significant.
Note that although this ordering is mandatory for this
mapping, there are NO implications on ordering significance
within X.400, where this is a Management Domain issue.
4.3.4. RFC 822 -> X.400
There are two basic cases:
1. X.400 addresses encoded in RFC 822. This will also include
RFC 822 addresses which are given reversible encodings.
2. "Genuine" RFC 822 addresses.
The mapping should proceed as follows, by first assuming case 1).
STAGE I.
1. If the 822-address is not of the form:
local-part "@" domain
Go to stage II.
NOTE:It may be appropriate to reduce a source route address
to this form by removal of all bar the last domain. In
terms of the design intentions of RFC 822, this would
be an incorrect action. However, in most real cases,
it will do the "right" thing and provide a better
service to the end user. This is a reflection on the
excessive and inappropriate use of source routing in
RFC 822 based systems. Either approach, or the
intermediate approach of stripping only domain
references which reference the local gateway are
conformant to this specification.
2. Attempt to parse EBNF.domain as:
*( domain-syntax "." ) known-domain
Where EBNF.known-domain is the longest possible match in a
list of supported mappings (see Appendix F). If this fails,
and the EBNF.domain does not explicitly identify the local
gateway, go to stage II. If it succeeds, allocate the
attributes associated with EBNF.known-domain, and
systematically allocate the attributes implied by each
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RFC 1138 Mapping X.400(88) and 822 December 1989
EBNF.domain-syntax component. If the domain explicitly
identifies the gateway, allocate no attributes.
3. If the local-part contains any characters not in
PrintableString, go to stage II.
4. If the 822.local-part uses the 822.quoted-string encoding,
remove this quoting. Parse the (unquoted) 822.local-part
according to the EBNF EBNF.std-or-address. If this parse
fails, parse the local-part according to the EBNF
EBNF.encoded-pn. The result is a set of type/value pairs.
If the values generated conflict with those derived in step
2 (e.g., a duplicated country attribute), the domain should
be assumed to be an RFC 987 gateway. In this case, take
only the LHS derived attributes. Otherwise add LHS and RHS
derived attributes together.
5. Associate the EBNF.attribute-value syntax (determined from
the identified type) with each value, and check that it
conforms. If not, go to stage II.
6. Ensure that the set of attributes conforms both to the
MTS.ORAddress specification and to the restrictions on this
set given in X.400. If not go to stage II.
7. Build the O/R Address from this information.
STAGE II.
This will only be reached if the RFC 822 EBNF.822-address is not
a valid X.400 encoding. If the address is an 822-MTS recipient
address, it must be rejected, as there is a need to interpret
such an address in X.400. For the 822-MTS return address, and
any addresses in the RFC 822 header, they should now be encoded
as RFC 822 addresses in an X.400 O/R Name:
1. Convert the EBNF.822-address to PrintableString, as
specified in Chapter 3.
2. The "RFC-822" domain defined attribute should be generated
from this string.
3. Build the rest of the O/R Address in the local Management
Domain agreed manner, so that the O/R Address will receive a
correct global interpretation.
Note that the domain defined attribute value has a maximum length
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of MTS.ub-domain-defined-attribute-value-length (128). If this
is exceeded by a mapping at the MTS level, then the gateway
should reject the message in question. If this occurs at the
IPMS level, then the action should depend on the policy being
taken, which is discussed in Section 5.1.3.
4.3.5. X.400 -> RFC 822
There are two basic cases:
1. RFC 822 addresses encoded in X.400.
2. "Genuine" X.400 addresses. This may include symmetrically
encoded RFC 822 addresses.
When a MTS Recipient O/R Address is interpreted, gatewaying will be
selected if there a single "RFC-822" domain defined attribute
present. In this case, use mapping A. For other O/R Addresses
which:
1. Contain the special attribute.
AND
2. Identifies the local gateway or any other known gateway with
the other attributes.
Use mapping A. In other cases, use mapping B.
NOTE:
A pragmatic approach would be to assume that any O/R
Address with the special domain defined attribute identifies
an RFC 822 address. This will usually work correctly, but is
in principle not correct.
Mapping A
1. Map the domain defined attribute value to ASCII, as defined
in Chapter 3.
Mapping B
This will be used for X.400 addresses which do not use the explicit
RFC 822 encoding.
1. For all string encoded attributes, remove any leading or
trailing spaces, and replace adjacent spaces with a single
space.
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2. Noting the hierarchy specified in 4.3.1, determine the
maximum set of attributes which have an associated domain
specification. If no match is found, allocate the domain as
the domain specification of the local gateway, and go to
step 4.
3. Following the 4.3.1 hierarchy and noting any omitted
components implied by the mapping tables (see Appendix F),
if each successive component exists, and conforms to the
syntax EBNF.domain-syntax (as defined in 4.3.1), allocate
the next subdomain. At least one attribute of the X.400
address should not be mapped onto subdomain, as
822.local-part cannot be null.
4. If the remaining components are personal-name components,
conforming to the restrictions of 4.2.1, then EBNF.encoded-
pn should be derived to form 822.local-part. In other cases
the remaining components should simply be encoded as a
822.local-part using the EBNF.std-or-address syntax. If
necessary, the 822.quoted-string encoding should be used.
If the derived 822.local-part can only be encoded by use of
822.quoted-string, then use of the mapping defined
in [Kille89b] may be appropriate. Use of this mapping is
discouraged.
4.4. Repeated Mappings
The mappings defined are symmetrical and reversible across a single
gateway. The symmetry is particularly useful in cases of (mail
exploder type) distribution list expansion. For example, an X.400
user sends to a list on an RFC 822 system which he belongs to. The
received message will have the originator and any 3rd party X.400 O/R
Addresses in correct format (rather than doubly encoded). In cases
(X.400 or RFC 822) where there is common agreement on gateway
identification, then this will apply to multiple gateways.
When a message traverses multiple gateways, the mapping will always
be reversible, in that a reply can be generated which will correctly
reverse the path. In many cases, the mapping will also be
symmetrical, which will appear clean to the end user. For example,
if countries "AB" and "XY" have RFC 822 networks, but are
interconnected by X.400, the following may happen: The originator
specifies:
Joe.Soap@Widget.PTT.XY
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This is routed to a gateway, which generates:
C = "XY"
ADMD = "PTT"
PRMD = "Griddle MHS Providers"
Organisation = "Widget Corporation"
Surname = "Soap"
Given Name = "Joe"
This is then routed to another gateway where the mapping is reversed
to give:
Joe.Soap@Widget.PTT.XY
Here, use of the gateway is transparent.
Mappings will only be symmetrical where mapping tables are defined.
In other cases, the reversibility is more important, due to the (far
too frequent) cases where RFC 822 and X.400 services are partitioned.
The syntax may be used to source route. THIS IS STRONGLY
DISCOURAGED. For example:
X.400 -> RFC 822 -> X.400
C = "UK"
ADMD = "Gold 400"
PRMD = "UK.AC"
"RFC-822" = "/PN=Duval/DD.Title=Manager/(a)Inria.ATLAS.FR"
This will be sent to an arbitrary UK Academic Community gateway by
X.400. Then it will be sent by JNT Mail to another gateway
determined by the domain Inria.ATLAS.FR (FR.ATLAS.Inria). This will
then derive the X.400 O/R Address:
C = "FR"
ADMD = "ATLAS"
PRMD = "Inria"
PN.S = "Duval"
"Title" = "Manager"
Similarly:
RFC 822 -> X.400 -> RFC 822
"/C=UK/ADMD=BT/PRMD=AC/RFC-822=jj(a)seismo.css.gov/"
@monet.berkeley.edu
This will be sent to monet.berkeley.edu by RFC 822, then to the AC
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RFC 1138 Mapping X.400(88) and 822 December 1989
PRMD by X.400, and then to jj@seismo.css.gov by RFC 822.
4.5. Directory Names
Directory Names are an optional part of O/R Name, along with O/R
Address. The RFC 822 addresses are mapped onto the O/R Address
component. As there is no functional mapping for the Directory Name
on the RFC 822 side, a textual mapping should be used. There is no
requirement for reversibility in terms of the goals of this
specification. There may be some loss of functionality in terms of
third party recipients where only a directory name is given, but this
seems preferable to the significant extra complexity of adding a full
mapping for Directory Names.
4.6. MTS Mappings
The basic mappings at the MTS level are:
1) 822-MTS originator ->
MTS.PerMessageSubmissionFields.originator-name
MTS.OtherMessageDeliveryFields.originator-name ->
822-MTS originator
2) 822-MTS recipient ->
MTS.PerRecipientMessageSubmissionFields
MTS.OtherMessageDeliveryFields.this-recipient-name ->
822-MTS recipient
822-MTS recipients and return addresses are encoded as EBNF.822-
address.
The MTS Originator is always encoded as MTS.OriginatorName, which
maps onto MTS.ORAddressAndOptionalDirectoryName, which in turn maps
onto MTS.ORName.
4.6.1. RFC 822 -> X.400
From the 822-MTS Originator, use the basic ORAddress mapping, to
generate MTS.PerMessageSubmissionFields.originator-name (MTS.ORName),
without a DirectoryName.
For recipients, the following settings should be made for each
component of MTS.PerRecipientMessageSubmissionFields.
recipient-name
This should be derived from the 822-MTS recipient by the
basic ORAddress mapping.
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originator-report-request
This should be set according to content return policy, as
discussed in Section 5.2.
explicit-conversion
This optional component should be omitted, as this service
is not needed.
extensions
The default value (no extensions) should be used.
4.6.2. X.400 -> RFC 822
The basic functionality is to generate the 822-MTS originator and
recipients. There is information present on the X.400 side, which
cannot be mapped into analogous 822-MTS services. For this reason,
new RFC 822 fields are added for the MTS Originator and Recipients.
The information discarded at the 822-MTS level should be present in
these fields. There may also be the need to generate a delivery
report.
4.6.2.1. 822-MTS Mappings
Use the basic ORAddress mapping, to generate the 822-MTS originator
(return address) from MTS.OtherMessageDeliveryFields.originator-name
(MTS.ORName). If MTS.ORName.directory-name is present, it should be
discarded.
The 822-MTS recipient is conceptually generated from
MTS.OtherMessageDeliveryFields.this-recipient-name. This is done by
taking MTS.OtherMessageDeliveryFields.this-recipient-name, and
generating an 822-MTS recipient according to the basic ORAddress
mapping, discarding MTS.ORName.directory-name if present. However,
if this model was followed exactly, there would be no possibility to
have multiple 822-MTS recipients on a single message. This is
unacceptable, and so layering is violated. The mapping needs to use
the MTA level information, and map each value of
MTA.PerRecipientMessageTransferFields.recipient-name, where the
responsibility bit is set, onto an 822-MTS recipient.
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 should be set to the same value as the
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822-MTS originator. In addition, if
MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName) contains
MTS.ORName.directory-name then this Directory Name should be
represented in an 822.comment.
Recipient names, taken from each value of
MTS.OtherMessageDeliveryFields.this-recipient-name and
MTS.OtherMessageDeliveryFields.other-recipient-names should be made
available to the RFC 822 user by use of the "X400-Recipients:" field.
By taking the recipients at the MTS level, disclosure of recipients
will be dealt with correctly. If any MTS.ORName.directory-name is
present, it should be represented in an 822.comment. If
MTS.OtherMessageDeliveryFields.orignally-intended-recipient-name is
present, then it should be represented in an associated 822.comment,
starting with the string "Originally Intended Recipient".
In addition, the following per-recipient services from
MTS.OtherMessageDeliveryFields.extensions should be represented in
comments if they are used. None of these services can be provided on
RFC 822 networks, and so in general these will be informative strings
associated with other MTS recipients. In some cases, string values
are defined. For the remainder, the string value may be chosen by
the implementor. If the parameter has a default value, then no
comment should be inserted.
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)".
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4.6.2.3. Delivery Report Generation
If MTA.PerRecipientMessageTransferFields.per-recipient-indicators
requires a positive delivery notification, this should be
generated by the gateway. Supplementary Information should be
set to indicate that the report is gateway generated.
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 should be used to generate
MTS.MTSIdentifier.global-domain-identifier.
MTS.MTSIdentifier.local-identifier should be set to the
822.msg-id, including the braces "<" and ">". If this string is
longer than MTS.ub-local-id-length (32), then it should be
truncated to this length.
The reverse mapping is not used in this specification. It
would be applicable where MTS.MTSIdentifier.local-identifier is
of syntax 822.msg-id, and it algorithmically identifies
MTS.MTSIdentifier.
4.7. IPMS Mappings
All RFC 822 addresses are assumed to use the 822.mailbox syntax.
This should include all 822.comments associated with the lexical
tokens of the 822.mailbox. In the IPMS O/R Names are encoded as
MTS.ORName. This is used within the IPMS.ORDescriptor,
IPMS.RecipientSpecifier, and IPMS.IPMIdentifier. An asymmetrical
mapping is defined between these components.
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 should be built consisting of (if present):
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- The 822.phrase component if the 822.address is an
822.phrase 822.route-addr construct.
- Any 822.comments, in order, retaining the parentheses.
This string should then be encoded into T.61 us a human
oriented mapping (as described in Chapter 3). If the string
is not null, it should be assigned to
IPMS.ORDescriptor.free-form-name.
3. IPMS.ORDescriptor.telephone-number should be omitted.
If IPMS.ORDescriptor is being used in IPMS.RecipientSpecifier,
IPMS.RecipientSpecifier.reply-request and
IPMS.RecipientSpecifier.notification-requests should be set to
default values (none and false).
If the 822.group construct is present, any included 822.mailbox
should be encoded as above to generate a separate IPMS.ORDescriptor.
The 822.group should be mapped to T.61, and a IPMS.ORDescriptor with
only an free-form-name component built from it.
4.7.2. X.400 -> RFC 822
Mapping from IPMS.ORDescriptor to RFC 822 address. In the basic
case, where IPMS.ORDescriptor.formal-name is present, proceed as
follows.
1. Encode IPMS.ORDescriptor.formal-name (MTS.ORName) as
EBNF.822-address.
2a. If IPMS.ORDescriptor.free-form-name is present, convert it
to ASCII (Chapter 3), and use this as the 822.phrase
component of 822.mailbox using the 822.phrase 822.route-addr
construct.
2b. If IPMS.ORDescriptor.free-form-name is absent. If
EBNF.822-address is parsed as 822.addr-spec use this as the
encoding of 822.mailbox. If EBNF.822-address is parsed as
822.route 822.addr-spec, then a 822.phrase taken from
822.local-part should be added.
3. If IPMS.ORDescriptor.telephone-number is present, this
should be placed in an 822.comment, with the string "Tel ".
The normal international form of number should be used. For
example:
(Tel +44-1-387-7050)
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4. If IPMS.ORDescriptor.formal-name.directory-name is present,
then a text representation should be placed in a trailing
822.comment.
5. If IPMS.RecipientSpecifier.report-request has any non-
default values, then an 822.comment "(Receipt Notification
Requested)", and/or "(Non Receipt Notification Requested)",
and/or "(IPM Return Requested)" should be appended to the
address. The effort of correlating P1 and P2 information is
too great to justify the gateway sending Receipt
Notifications.
6. If IPMS.RecipientSpecifier.reply-request is True, an
822.comment "(Reply requested)" should be appended to the
address.
If IPMS.ORDescriptor.formal-name is absent, IPMS.ORDescriptor.free-
form-name should be converted to ASCII, and used as 822.phrase within
the RFC 822 822.group syntax. For example:
Free Form Name ":" ";"
Steps 3-6 should then be followed.
4.7.3. IP Message IDs
There is a need to map both ways between 822.msg-id and
IPMS.IPMIdentifier. This allows for X.400 Receipt Notifications,
Replies, and Cross References to reference an RFC 822 Message ID,
which is preferable to a gateway generated ID. A reversible and
symmetrical mapping is defined. This allows for good things to
happen when messages pass multiple times across the X.400/RFC 822
boundary.
An important issue with messages identifiers is mapping to the exact
form, as many systems use these ids as uninterpreted keys. The use
of table driven mappings is not always symmetrical, particularly in
the light of alternative domain names, and alternative management
domains. For this reason, a purely algorithmic mapping is used. A
mapping which is simpler than that for addresses can be used for two
reasons:
- There is no major requirement to make message IDs "natural"
- There is no issue about being able to reply to message IDs.
(For addresses, creating a return path which works is more
important than being symmetrical).
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The mapping works by defining a way in which message IDs generated on
one side of the gateway can be represented on the other side in a
systematic manner. The mapping is defined so that the possibility of
clashes is is low enough to be treated as impossible.
4.7.3.1. 822.msg-id represented in X.400
IPMS.IPMIdentifier.user is omitted. The IPMS.IPMIdentifier.user-
relative-identifier is set to a printable string encoding of the
822.msg-id with the angle braces ("<" and ">") removed.
4.7.3.2. IPMS.IPMIdentifier represented in RFC 822
The 822.domain of 822.msg-id is set to the value "MHS". The
822.local-part of 822.msg-id is built as:
[ printablestring ] "*" [ std-or-address ]
with EBNF.printablestring being the IPMS.IPMIdentifier.user-
relative-identifier, and std-or-address being an encoding of the
IPMS.IPMIdentifier.user. If necessary, the 822.quoted-string
encoding is used. For example:
<"147*/S=Dietrich/O=Siemens/ADMD=DBP/C=DE/"@MHS>
4.7.3.3. 822.msg-id -> IPMS.IPMIdentifier
If the 822.local-part can be parsed as:
[ printablestring ] "*" [ std-or-address ]
and the 822.domain is "MHS", then this ID was X.400 generated. If
EBNF.printablestring is present, the value is assigned to
IPMS.IPMIdentifier.user-relative-identifier. If EBNF.std-or-address
is present, the O/R Address components derived from it are used to
set IPMS.IPMIdentifier.user.
Otherwise, this is an RFC 822 generated ID. In this case, set
IPMS.IPMIdentifier.user-relative-identifier to a printable string
encoding of the 822.msg-id without the angle braces.
4.7.3.4. IPMS.IPMIdentifier -> 822.msg-id
If IPMS.IPMIdentifier.user is absent, and IPMS.IPMIdentifier.user-
relative-identifier mapped to ASCII and angle braces added parses as
822.msg-id, then this is an RFC 822 generated ID.
Otherwise, the ID is X.400 generated. Use the
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IPMS.IPMIdentifier.user to generate an EBNF.std-or-address form
string. Build the 822.local-part of the 822.msg-id with the syntax:
[ printablestring ] "*" [ std-or-address ]
The printablestring is taken from IPMS.IPMIdentifier.user-relative-
identifier. Use 822.quoted-string if necessary. The 822.msg-id is
generated with this 822.local-part, and "MHS" as the 822.domain.
4.7.3.5. Phrase form
In "Reply-To:" and "References:", the encoding 822.phrase may be used
as an alternative to 822.msg-id. To map from 822.phrase to
IPMS.IPMIdentifier, assign IPMS.IPMIdentifier.user-relative-
identifier to the phrase. When mapping from IPMS.IPMIdentifier for
"Reply-To:" and "References:", if IPMS.IPMIdentifier.user is absent
and IPMS.IPMIdentifier.user-relative-identifier does not parse as
822.msg-id, generate an 822.phrase rather than adding the domain MHS.
4.7.3.6. RFC 987 backwards compatibility
The mapping proposed here is different to that used in RFC 987, as
the RFC 987 mapping lead to changed message IDs in many cases.
Fixing the problems is preferable to retaining backwards
compatibility. An implementation of this standard is encouraged to
recognise message IDs generated by RFC 987.
Chapter 5 -- Detailed Mappings
This chapter gives detailed mappings for the functions outlined in
Chapters 1 and 2. It makes extensive use of the notations and
mappings defined in Chapters 3 and 4.
5.1. RFC 822 -> X.400
5.1.1. Basic Approach
A single IP Message is generated. The RFC 822 headers are used to
generate the IPMS.Heading. The IP Message will have one IA5
IPMS.BodyPart containing the RFC 822 message body.
Some RFC 822 fields cannot be mapped onto a standard IPM Heading
field, and so an extended field is defined in Section 5.1.2. This is
then used for fields which cannot be mapped onto existing services.
The message is submitted to the MTS, and the services required can be
defined by specifying MTS.MessageSubmissionEnvelope. A few
parameters of the MTA Abstract service are also specified, which are
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not in principle available to the MTS User. Use of these services
allows RFC 822 MTA level parameters to be carried in the analogous
X.400 service elements. The advantages of this mapping far outweigh
the layering violation.
5.1.2. X.400 Extension Field
An IPMS Extension is defined:
rfc-822-field HEADING-EXTENSION
VALUE RFC822Field
::= id-rfc-822-field
RFC822Field ::= IA5String
The Object Identifier id-rfc-822-field is defined in Appendix D.
To encode any RFC 822 Header using this extension, the RFC822Field
should be set to the 822.field omitting the trailing CRLF (e.g.,
"Fruit-Of-The-Day: Kiwi Fruit"). Structured fields should be
unfolded. There should be no space before the ":". The reverse
mapping builds the RFC 822 field in a straightforward manner.
5.1.3. Generating the IPM
The IPM (IPMS Service Request) is generated according to the rules of
this section. The IPMS.IPM.body usually consists of one
IPMS.BodyPart of type IPMS.IA5TextbodyPart with
IPMS.IA5TextBodyPart.parameters.repertoire set to the default (ia5)
which contains the body of the RFC 822 message. The exception is
where there is a "Comments:" field in the RFC 822 header.
If no specific 1988 features are used, the IPM generated should be
encoded as content type 2. Otherwise, it should be encoded as
content type 22. The latter will always be the case if extension
heading fields are generated.
When generating the IPM, the issue of upper bounds must be
considered. At the MTS and MTA level, this specification is strict
about enforcing upper bounds. Three options are available at the IPM
level. Use of any of these options conforms to this standard.
1. Ignore upper bounds, and generate messages in the natural
manner. This assumes that if any truncation is done, it
will happen at the recipient UA. This will maximise
transfer of information, but may break some recipient UAs.
2. Reject any inbound message which would cause a message
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violating constraints to be generated. This will be robust,
but may prevent useful communication.
3. Truncate fields to the upper bounds specified in X.400.
This will prevent problems with UAs which enforce upper
bounds, but will sometimes discard useful information.
These choices have different advantages and disadvantages, and the
choice will depend on the exact application of the gateway.
The rest of this section concerns IPMS.IPM.heading (IPMS.Heading).
The only mandatory component of IPMS.Heading is the
IPMS.Heading.this-IPM (IPMS.IPMIdentifier). A default should be
generated by the gateway. With the exception of "Received:", the
values of multiple fields should be merged (e.g., If there are two
"To:" fields, then the mailboxes of both should be used).
Information should be generated from the standard RFC 822 Headers as
follows:
Date:
Ignore (Handled at MTS level)
Received:
Ignore (Handled at MTA level)
Message-Id:
Mapped to IPMS.Heading.this-IPM. For these, and all other
fields containing 822.msg-id the mappings of Chapter 4 are
used for each 822.msg-id.
From:
If Sender: is present, this is mapped to
IPMS.Heading.authorizing-users. If not, it is mapped to
IPMS.Heading.originator. For this, and other components
containing addresses, the mappings of Chapter 4 are used
for each address.
Sender:
Mapped to IPMS.Heading.originator.
Reply-To:
Mapped to IPMS.Heading.reply-recipients.
To: Mapped to IPMS.Heading.primary-recipients
Cc: Mapped to IPMS.Heading.copy-recipients.
Bcc: Mapped to IPMS.Heading.blind-copy-recipients.
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In-Reply-To:
If there is one value, it is mapped to
IPMS.Heading.replied-to-IPM, using the 822.phrase or
822.msg-id mapping as appropriate. If there are several
values, they are mapped to IPMS.Heading.related-IPMs, along
with any values from a "References:" field.
References:
Mapped to IPMS.Heading.related-IPMs.
Keywords:
Mapped onto a heading extension.
Subject:
Mapped to IPMS.Heading.subject. The field-body uses the
human oriented mapping referenced in Chapter 3 from ASCII to
T.61.
Comments:
Generate an IPMS.BodyPart of type IPMS.IA5TextbodyPart with
IPMS.IA5TextBodyPart.parameters.repertoire set to the
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