This is the Frequently Asked Questions file for the mailing list MHSNEWS/newsgroup comp.protocols.iso.X400

It is sent to the list on the first of every month. The latest revision is also available from the Web site (html format) (text format)

$Revision: 1.4 $ $Date: 1997/11/07 15:10:59 $

4) Where can I FTP the X.400 standards?
5) Where can I find more information about X.400 and OSI?
6) How do I send Telefax from X.400?
7) On which type of network may I use X.400
8) What books should i read on X.400?
9) What is my X.400 address?
10) Why does mail to /..../@gateway fail?



1) What is X.400?

X.400 is the short name for the set of standards from ISO and the ITU that describe a messaging service; the transport of interpersonal messages (email) being one (the most prolific) application of the service.
It is the only non-proprietary standard for interchange of electronic mail that has the sanction of an official standards body, if you don't consider the IETF such a body.

(ITU-TS, the International Telecommunications Union Telecommunication Standard Sector, was formerly named CCITT).

It currently exists in 2 flavours:

Further updates have been made after 1988, but nothing that breaks 1988 implementations. Details of the standards involved can be found in the standards list on this document's webserver.


This depends on what you are asking for.

SMTP has got:

X.400 has got:

The differences are too deep for a simple summary; see the Webserver X400-Internet Debate at for the details.


Answer: Lots. A partial list is found on the Web server at, and is also posted to the newsgroup once a month.

4) Where can I FTP the X.400 standards?

The issue of FTPing standards is painful, to say the least.

The ITU put up a really nice Web server at, which includes most of the relevant recommendations, but then, in June 1995, they closed document access to all but subscribers. See, but don't touch....

ISO documents cannot in general be put online. In some cases, the authors have placed copies of last-version drafts online, since drafts are not copyrighted by ISO. In other cases, special arrangements have been made to put certain ISO standards (like the CLNS spec) online.

They are available (at cost) from your local standards body. Some organizations also provide subscription services and provide copies of the standards.

Read the "standards FAQ" of comp.protocols.iso for more info.

5) Where can I find more information about X.400 and OSI?

There is various information on the FTP server at Uni-Erlangen: use ftp to and log in as "anonymous" with your e-mail address as password. Look in the directory pub/doc/ISO/english. There are a lot of files containing USENET articles and other sources of information about OSI protocols and related ISO/ITU standards. The file INDEX contains a summary of the contents.

Markus Kuhn <>, who kindly supplied me with this information, maintains this archive. Please contact him if you have additional interesting files.

Other interesting places, supplied by Markus Kuhn:   pub/doc/ISO           collected USENET articles etc.            networking/osi        ISODE and other OSI stuff
                      networking/x25           protocols             DoD and GOSIP related stuff
                      rfc                   RFC Repository          src                   ISODE, PP, OSIMIS, ...
                      osi-ds                Internet X.500 documents
                      ietf-osi-oda          Internet ODA documents        ietf/mhs-ds           X.500 based routing drafts        pub/SGML              SGML/HyTime related things  info/standards        various documents
                      info/osi-rus          X.400/X.500 papers          CCR                   IEEE CCR articles            isode                 ISODE 8.0

6) How do I send Telefax from X.400?

The answer, as usual, is "ask your service provider". The most common schemes: A lot of variants exist with more or less the same scheme.


X.400 '84 has been defined to run over a standard OSI stack (X.25, TP0, BAS Session), thus most implementations, and all that pass conformance tests, are able to run over a X.25 network. Often these implementations have a X.25 or a transport level interface with manufacturers supplied lower layers. In the case of transport-level, X.400 is thus able to run over CLNS as long as this is supported under the Tli or XTi.

However, in order to enable use of TCP/IP network, many implementations offer RFC1006 (TP0 over TCP/IP) access. This is almost mandatory within TCP/IP based LAN and a real plus for the R&D community which maily use TCP/IP WANs.

Additionaly a few implementations such as PP/ISODE and M.PLUS/UCOM.X come along with an RFC1006 TS-bridge which act as a relay between X.25 and TCP/IP network for OSI applications such as X.400 and X.500.

The MAP/TOP profiles also specify (and use) X.400 for use over TP4 across any 802.x LAN (such as Ethernet or FDDI).

Finally, many X.400 implementations for PCs or Mac have been developped to use what exists in the PC arena such as PC-NFS, NETBios, X.32 or even dialup over modems. Carefully check what is available with your favourite supplier!


In spite of the large interest on the topic, there does not seem to be many specific X.400 books around.

The ones that have been mentioned are:

  X400 Message Handling, Standards, Interworking, Applications
  by B. Plattner, C. Lanz, H. Lubich, M. M"uller and T. Walter
    of the Swiss Federal Institute of Technology (ETH), Zurich
  It was translated by Stephen S. Wilson
  Published by Addison-Wesley, 1991, data communications and networks series
  ISBN 0-201-56503-X
  Price approximately USD 41

  The German edition is named:
  Elektronische Post und Datenkommunikation: 
  X.400: Die Normen und ihre Anwendung.
  Bonn: Addison-Wesley, 1989

  It includes:
  - Basics of the OSI reference model and the X.400 MHS model
  - Stuff about interworking (mentioning RARE MHS!), EDI and more
  - Improvements of X.400 from 84 to 88, and the problems in interworking
  - A lot of useful appendices.
Information by Marcel Mink <>
Also mentioned by:
Philipp Hoschka <>
David McAnally <>

  Carl-Uno Manros
  The X.400 blue book companion
  Twickenham: Technology Appraisals, 1989.
  ISBN: 1-871802008

  Not very detailed, but helps if one also reads the standard "in parallel".

Information by Philipp Hoschka <>

  Robert Babatz, Manfred Bogen und Uta Pankoke-Babatz
  Elektronische Kommunikation - X.400
  Braunschweig: Vieweg, 1990.
  ISBN: 3-528-06389-0

  Very helpful, but in German. There might be plans for
  an English edition, though.

Information by Philipp Hoschka <>

  Sara Radicati
  Electronic Mail, an introduction to the X.400 Message Handling Standards
  McGraw-Hill 1992 (Uyless Black series on computer communication)
  ISBN: 0-07-051104-7

  Fairly comprehensible and readable. A good introductory text

Information by Erik Skovgaard <>
Mentioned by Hans P. Holen <>

  Introduction to X.400, by Cemil Betanov. Artech House, 1993, ISBN 
  0-89006-597-7. A rather complete introduction to X.400 with a comprehensive
  subject index at the end.

Information by Jacob Palme <>
  "The E-Mail Frontier: Emerging markets and evolving technologies" by
  Daniel J.  Blum and David M. Litwack and published by
  Addison-Wesley. ISBN 0-201-56860

  It's not specifically for X.400 but describes all details necessary
  about it.  The main idea behind it is to give a good description of
  all issues relating to email use and design. It also includes good
  discussions on SMTP and X.400/SMTP interconnection issues

Information by (Hiro Daryanani)

9) What is my X.400 address?

If you have an Internet address of the form, there are two alternatives for your X.400 address:

EITHER there is a defined mapping onto standard attributes for your domain, so that, for instance

           maps to

   C=no;ADMD= ;PRMD=uninett;O=sintef;OU=delab;S=Alvestrand;G=Harald
OR there is no such mapping, and you will have to use a Domain Defined Attribute:

       maps to

  <Std. Attributes of a gateway>;DD.RFC-822=Someone(a)
The following characers have special conversion rules when used in DDAs:

@       ->      (a)     at sign
!       ->      (b)     exclamation point (bang)
%       ->      (p)     percent sign
_       ->      (u)     underscore

All the hoary details may be found in RFC 1327. A more readable version is the COSINE addressing user guide, found at


Feb 15  1993 addressing-english-250193.txt
Feb 15  1993
Sep 27  1993 addressing-german-dfn-0993.txt
Feb 15  1993 addressing-german-dfn-1092.txt
Feb 15  1993
Sep 10  1993 e-mail_user_guide_it_garr.hqx
Sep 10  1993 e-mail_user_guide_it_garr.mac-binary
Sep 10  1993
NOTE: The actual mapping information in the user guides is rather dated by now; the theory is still sound!

A Web form for translation is at

A few places where you can use TELNET to a port, type in your address and see what it maps to, are:

These services are also available via X.25 PAD and e-mail; get the addressing guide mentioned above for the details.

NOTE: If you use gateways that do not conform to RFC 987, RFC 1148 or RFC 1327, all bets are off. For instance, the kindest description of the result of passing through the gateways of some commercial X.400 service providers is "interesting".

A list of known gateways is provided in the companion document, "FAQ-gateways.text".

10) Why does mail to /..../@gateway fail?

This is a bug of long standing.

Typically, you see a message like:

<< /...../@gateway: Cannot mail directly to files
This has a long and convoluted history. Usually, it involves a mailer that knows how to do UUCP.

It turns out that one program used in UUCP (uuxqt) is capable of executing a large set of commands, some of which may destroy important files if given filename arguments.

So, in order to protect this from happening, HDB UUCP will follow in the tradition of fixing loose thumbtacks with sledgehammers, and refuse to accept any command that has an argument that looks like a filename that is relative to the root.

In the common UUCP setup, where only rmail and rnews are permitted, this does not make sense, but it is not possible to turn it off.

In Taylor UUCP, it is a compile time option. (This information supplied by Ian Lance Taylor <>)

Another "nice" feature that helps in causing this is the "s" flag in the Sendmail mailer definition. This strips the quotes off the local part of the address, so that "/..../"@gateway gets turned into /..../@gateway, which easily makes things go haywire, for instance by separating the address onto multiple lines or interpreting it as multiple recipients because of embedded spaces.
This flag should be nuked on all mailers except the "local" and "prog" mailers. Unfortunately, SUN ships it on all mailers by default, but then, anyone who uses a SUN default Sendmail configuration has problems anyway.
Last modified: Mon Oct 27 10:22:17 1997