M-Switch X.400 Conformance

M-Switch X.400 is a high performance, highly flexible and robust X.400 Message Transfer Agent (MTA). M-Switch X.400 includes two full featured and conformant X.400 protocol implementations:

X.400 P1 for transfer to other MTAs.
X.400 P3 for connection to Message Stores and User Agents.

This page gives a brief overview of X.400 conformance, and sets out the conformance of M-Switch X.400.

The X.400 Standards and ISPs

The base X.400 standards and ISPs (International Standard Profiles) are set by two bodies.

The ITU (International Telecommunications Union) as a series of documents collectively referred to as X.400. There are a number of documents in this series (e.g., X.400, X.402, X.420).
ISO (International Organization for Standardization) and IEC (International Electrotechnical Commission) as MOTIS (Message Oriented Text Interchange Systems) and the ISO/IEC 10021 series. These documents are equivalent (e.g., ISO/IEC 10021-7 is equivalent to X.420).

The ITU and ISO documents are technically aligned. There are some small differences because the ITU documents relate only to interconnection with public services, whereas the ISO/IEC documents also cover "local" issues. Isode supports these differences, which relate to different deployment situations, and do not affect interoperability.

The ISO documents generally have later publication dates, which vary between different documents in the series series and can be as much as five years later than the equivalent ITU numbers. The ITU documents have more consistent dating, which more clearly reflects when the specifications were developed. This difference reflects the different publication procedures of the organizations. Because of this, the dates referred to here are the ITU dates. The following versions of X.400 have been issued.

1984. The original X.400 series.
1988. A major update to all documents.
1994-6. Updates to some of the X.400 documents were issued in these years.
1999. Updates and a full release of the complete series.

X.400 specifies a number of components, including MTA, Message Store and User Agent. X.400(88) is the most important specification for a modern X.400 system. The MTA related updates since this specification are relatively minor.

Optionality and Extensibility

X.400 contains many optional elements. Some of these elements are only applicable to certain special situations and types of configuration (e.g., the mappings from X.400 to paper postal service). Conformance needs to be viewed in the context of the elements that are actually needed, rather than a simple implementation of all features.

An important change in X.400(1988) was the addition of a series of extensibility mechanisms for various parts of the protocol. This means that most changes to X.400 subsequent to the 1988 version have been introduced in a manner which is compatible with X.400(1988) implementations, in that an implementation can be aware of an extension it does not support and whether or not support of the extension is critical.

Functional Groups and ISPs

In order to deal with specification of an X.400 system, there are a series of ISPs (International Standard Profiles) published in conjunction with the base X.400 specifications. "ISO/IEC 10611-1: Common Messaging Part 1: MHS Service Support (1999)" sets out a core framework for the X.400 ISPs. In particular it defines a set of functional groups, to which an implementation can claim conformance.

For each functional group, there is a list of mandatory features (which may be optional in the base standard) and a list of optional features. Each of the ISPs is structures as a PICS (Protocol Implementation Conformance Statement) proforma. The PICS Proforma can be completed for a specific implementation to form a PICS for that implementation. The PICS is a key document that specifies which features are implemented. To claim conformance for a functional group, all of the mandatory features for that functional group must be implemented.

X.400 Functional Groups in M-Switch X.400

This section lists all of the X.400 functional groups, and which ones are supported by M-Switch X.400.

Functional Group	M-Switch X.400 Support	Notes
Conversion (CV)	Supported
Distribution List (DL)	Supported
Physical Delivery (PD)	Not supported	All elements supported required of an MTA that is co-resident with a Physical Delivery Access Unit
Redirection (RED)	Supported
Latest Delivery (LD)	Supported
Return of Contents (RoC)	Supported
Security (SEC)	Supported to the S0 level	S1 level is supported for P1, but not for P3.
Use of Directory (DIR	Supported
1984 Interworking (84IW)	Supported, excluding internal trace information.
Simple Protected Password (SPP)	Not supported	Strong authentication is preferable
Redirection Instructions (RED2)	Not supported	Only relevant to MTS84 (AMH14), and not core MTA function
Delivery Constraints (DC)	Not supported	Only relevant to MTS84 (AMH14), and not core MTA function
Restricted Delivery (RD)	Not supported	Only relevant to MTS84 (AMH14), and not core MTA function

Message Transfer Conformance

An MTA must support Message Transfer, using the X.400 P1 protocol. M-Switch is conformant to the core ISP requirements for the 1984, 1988, and 1996, 1999 and 2003 versions of X.400.

Detailed specification of the Message Transfer Conformance of M-Switch X.400 is provided in two PICS statements:

Message Access Conformance

Message Access refers to submission and delivery using the X.400 P3 protocol. There are two versions of the X.400 P3 protocol:

P3 (1988), with conformance defined in AMH12 (MTS Access) and AMH 23 (IPM Requirements for MTS Access).
P3 (1994), with conformance defined in AMH14 (MTS94 Access) and AMH 25 (IPM Requirements for MTS94 Access). This defines additional end user management and control functions.

Extensions from X.400(1994) and X.400(1999) can be used with both of these protocols. Isode supports P3(1988) only.

Details of M-Switch X.400 P3 conformance is defined in "AMH12 and AMH14 - MTS Access (P3) and MTS 94 Access (P3)" ISO/IEC ISP 10611-4. This is aligned to ITU X.483 "P3 PICS".

Isode is conformant to the mandatory elements of the ISP for P3(1988), with two exceptions:

DeliveryControl operation is not supported. M-Switch X.400 achieves the functions of this operation by use of its own configuration management tools. This allows access to controls by P7 users and administrators, which increases flexibility.
For the MTS Forced Access protocol, M-Switch X.400 supports only delivery (and not submission). This reflects use of MTS Forced Access to deliver messages from M-Switch to a Message Store, where submission is not needed. P3 Clients can submit and deliver messages using MTS Access.

Lower Layers: X.400 and RTSE

The X.400 channels support the 1984, 1988 and 1992 recommendations including the mts-transfer (P1-1988, RTSE normal-mode), mts-transfer-protocol (P1-1988, RTSE X.410(1984)-mode) and mts-transfer-protocol-1984 (P1-1984, RTSE X.410(1984)-mode) application contexts.

Full RTSE recovery is supported for both inbound and outbound transfers. There is full support for Two Way Alternate. All three application contexts can be supported by a receiving channel on a single Session address.

Lower Layers: Transport

X.400 is usually operated over TCP/IP using ITOT (ISO Transport over TCP). Full details on ISO Transport support, including options for working to ISO TP4 (Transport Protocol Class 4) or over X.25 are given in ISO Transport Protocols.

X.400 Base Standards

ITU X.400 Message Handling System: System and Service Overview, ISO/IEC 10021-1, 1999

ITU F.401 Naming and addressing for public message handling services, 1999

ITU X.402 Message Handling Systems (MHS): Overall Structure, ISO/IEC 10021-2, 1999

ITU X.411 Message Handling Systems (MHS): Message Transfer System: Abstract Service Definition and Procedures, ISO/IEC 10021-4, 1999

ITU X.419 Message Handling Systems (MHS): Protocol Specifications, ISO/IEC 10021-6, 1999

ITU X.420 Message Handling Systems (MHS): Interpersonal Messaging System , ISO/IEC 10021-7, 1996

Other Conformance

ICAO	Manual of Technical Provisions for the Aeronautical Telecommunications Network (ATN).

RFC 1328	X.400 1988 to 1984 downgrading, S. Kille, May 1992

SARPS	ICAO SARPS Doc 9880/AN965:The ATN SARPS, Sub volume 3, Ground to Ground Applications, Fourth edition.

Isode Products

X.400 Messaging Products

Messaging Management