X.400 has an integrated directory service

This statement, in my honest opinion, is simply false.

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.

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.

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.

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