Postmaster Convention for X.400 Operations
Network Working Group A. Cargille
Request for Comments: 1648 University of Wisconsin
Category: Standards Track July 1994
Postmaster Convention for X.400 Operations
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Both STD 11, RFC 822  and STD 3, RFC 1123  (Host Requirements)
require that the email address "postmaster" be supported at all
hosts. This paper extends this concept to X.400 mail domains which
have registered RFC 1327 mapping rules, and which therefore appear to
have normal RFC822-style addresses.
1. Postmaster Convention in RFC822
Operating a reliable, large-scale electronic mail (email) network
requires cooperation between many mail managers and system
administrators. As noted in RFC 822 , often mail or system
managers need to be able to contact a responsible person at a remote
host without knowing any specific user name or address at that host.
For that reason, both RFC 822 and the Internet Host Requirements 
require that the address "postmaster" be supported at every Internet
2. Postmaster Convention and X.400
However, RFC 822 is not the only email protocol being used in the
Internet. Some Internet sites are also running the X.400 (1984) 
and X.400 (1988)  email protocols. RFC 1327 specifies how to map
between X.400 and RFC 822 addresses . When mapping rules are
used, addresses map cleanly between X.400 and RFC 822. In fact, it
is impossible to determine by inspecting the address whether the
recipient is an RFC 822 mail user or an X.400 mail user.
A paper by Rob Hagens and Alf Hansen describes an X.400 community
known as the "Global Open MHS Community" (GO-MHS) . Many mail
domains in the GO-MHS Community have registered RFC 1327 mapping
rules. Therefore, users in those domains have RFC 822-style email
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RFC 1648 X.400 Postmaster Convention July 1994
addresses, and these email domains are a logical extension of the RFC
822 Internet. It is impossible to tell by inspecting a user's
address whether the user receives RFC 822 mail or X.400 mail.
Since these addresses appear to be standard RFC 822 addresses, mail
managers, mailing list managers, host administrators, and users
expect to be able to simply send mail to "postmaster@domain" and
having the message be delivered to a responsible party. When an RFC
1327 mapping rule exists, the X.400 address element corresponding to
the left-hand-side "postmaster" is "Surname=Postmaster" (both 1984
and 1988). However, neither the X.400 protocols, North America X.400
Implementor's Agreements , nor the other regional X.400
implementor's agreements require that "Surname=Postmaster" and
"CommonName=Postmaster" be supported. (Supporting these addresses is
recommended in X.400 (1988)).
For mapped X.400 domains which do not support the postmaster
address(es), this means that an address such as "email@example.com"
might be valid, yet mail to the corresponding address
"firstname.lastname@example.org" fails. This is frustrating for remote
administrators and users, and can prevent operational problems from
being communicated and resolved. In this case, the desired seamless
integration of the Internet RFC 822 mail world and the mapped X.400
domain has not been achieved.
The X.400 mail managers participating in the Cosine MHS Project
discussed this problem in a meeting in June 1992 . The discussion
recognized the need for supporting the postmaster address at any
level of the address hierarchy where these are user addresses.
However, the group only required supporting the postmaster address
down to certain levels of the O/R Address tree. This approach solved
part of the problem, but not all of it. A more complete solution is
3. Proposed Solution
To fully achieve the desired seamless integration of email domains
for which RFC 1327 mapping rules have been defined, the following
convention must be followed,
If there are any valid addresses of the form "user@domain", then
the address "postmaster@domain" must also be valid.
To express this in terms of X.400: For every X.400 domain for which
an RFC 1327 mapping rule exists, if any address of the form
Surname=User; <Other X.400 Address Elements>
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