X.400 has an integrated directory service
This statement, in my honest opinion, is simply
The reason for its falsity is that X.400 today works perfectly well
(or at least as well as X.400 can function) without any
large scale directory service support.
It has to - apart from the million-entry, 5000-organization NameFlow-Paradise
pilot, there simply isn't any large scale X.500 directory to connect
to, and the X.400 standards do not admit of the existence of any
directory but X.500. (Paradise is an umbrella. You might know your
closest part of it under another name.)
What does exist, however, is specifications. The
X.400 standards specify:
All of these depend on the model of a single, globally accessible,
X.500-based Directory service.
- How to include a Directory Name along with the O/R name in
message headers and envelope
- How an UA can submit a message without filling in the O/R name,
only the Directory name (the MTA has to look it up, though)
- How a mailing list can be stored in the Directory, and some
hints about the processing to do when expanding it
- How information about X.400 deliverable body parts can be
stored in an user's Directory entry
The standards do not, however, specify:
What is specified isn't perfect either - the mailing list description
has the irritating property that it doesn't interwork well with the
Internet, since it doesn't change the P1 originator of the message,
but depends on the "DL expansion history" attribute for loop detection.
- how to find an user given his X.400 address (this is possible
using RFC 1836, an IETF Experimental standard)
- how to find out what body parts are supported if the recipient
himself is not listed in the Directory
- how to find out what MTA to send the message on to for
delivery (this is described in RFC 1801, another IETF
Experimental protocol; similar work has been languishing in ISO
for several years - the ITU refuses to touch it)
Some X.400 UAs offer a menu entry that can connect to a directory to
look up an entry, and then do copy/paste back into a message or an
address book; this is IMHO a Good Thing, which is also offered by some
Internet mailers, but hardly qualifies as a decisive difference
between the two mail systems.
Internet directory systems
The Internet's record of producing directories isn't exactly stellar
either. In the Internet, there are:
See the RFCs produced by the IDS and ASID working groups of the IETF
for more details.
- Specifications for using X.500 over the Internet
- Specifications for another directory, WHOIS++
- Lots and lots and lots of Web gateways to various services
- No deployed large uniform wide area directory apart from Paradise.
For mail routing and name resolution on the Internet, there is the
Domain Name Service, DNS, which has functioned reliably and
efficiently for a number of years, and has been critical for the
growth of the Internet. But this isn't a general directory, and never
will be. It does not support searching, for one thing.
I hope that an uniformly accessible, wide area directory service will
be created at some time in the future, and that messaging systems will
be able to use it efficiently and intelligently.
At the moment, however, it doesn't exist.
Last modified: Tue Aug 22 12:58:05 1995