The X.400 standards
This page is intended to be part of my X.400
The X.400 standards are published in cooperation by ISO and the ITU.
ISO calls them ISO/IEC
10021, parts 1 to 9; the X.400 name is the only one you need
to care about, since it is the only one people remember.
Within ISO, work is done by ISO/IEC JTC1/SC18,
"Document processing and related communication",
working group 4.
The main variants of X.400 are:
- X.400/1984 - published only by the CCITT (which is now
- X.400/1988 - a complete rewrite of the standards,
published jointly by ISO and X.400
- A number of updates to the standards, sometimes called
X.400/1993, but not published as a joint set.
X.400 is not a single standard, but a number of them, ranging
from X.400 to X.440.
The complete list of standards in force in the X series can be
fetched from the ITU Web
listing listing at http://www.itu.ch/
The currently relevant X.400 standards are:
(1993) Message handling system and service overview (also
called F.400) (ISO part 1)
(1995) Overall architecture (ISO part 2)
- X.407 (1988) Abstract service definition conventions (ISO
part 3) (not listed in the current Web site)
(1988) Encoded information type conversion rules (ITU
only; irrelevant; possibly replaced by a T-series
standard, but I haven't found any trace of it here)
(1995) Message transfer system: Abstract service
definition and procedures (the definition of the P1
protocol) (ISO part 4)
(1995) Message store: Abstract-service definition (ISO
(1995) Protocol specifications (what remains after
reading X.411 and X.413) (ISO part 6)
(1992) Interpersonal messaging system (ISO part 7)
COMFAX use of MHS (1994)
(1991) Electronic data interchange messaging system (ISO
parts 8 and 9; at DIS stage in Jan 95)
(1992) Voice messaging system (Amendment
Management model and architecture
The real protocol specifications are X.411, X.413, X.419 and
X.420. The rest are add-ons, supporting material, or irrelevant.
Totally irrelevant X-numbers include:
- X.403 (1988) Conformance testing (ITU only, X.400/84 (!)
specific, mostly irrelevant to understanding the
protocol); superseded by the X.480 series.
- X.409 (1984) - this was the first specification of what
is now X.208 and X.209, Abstract Syntax Notation One.
- X.410 (1984) - this was the first specifications of the
Remote Operations service and Reliable Transfer Service,
which is now X.218 and X.228 (RTSE), and X.219 and X.229
- X.445 (1995) - a profile for using OSI CONS over
telephones. The history of how this got into the X.400
series is politically interesting, but not terribly
In addition, X.480-X.485 specify PICS proformas for the
The standards are NOT available to the
general public online; for some reason, ISO and the ITU expect to
earn money from sales of paper copies of the standards. ITU also
sells electronic versions.
Some sites, like ULB,
have copies of the base standards online, but these are intended
for specific purposes.
Other relevant standards
There are a number of other standards that influence X.400 in
Some other sites to go look for links to interesting docs:
Last modified: Aug 23, 1998