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.

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
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.

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, 1992
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

RFC 1328 X.400 1988 to 1984 downgrading, S. Kille, May 1992
SARPS ICAO SARPS Doc 9880-AN/466 - Manual on detailed technical specifications for the Aeronautical Telecommunication Network using ISO/OSI standards and protocols, Part II - Ground-ground applications (ATSMHS) 1st Edition.