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
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>
is a valid address, then the address
Surname=Postmaster; <Same X.400 Address Elements>
must also be a valid address. If the X.400 system is running
X.400(1988), then the address
CommonName=Postmaster; <Same X.400 Address Elements>
must also be supported. (Note that CommonName=Postmaster will not be
generated by RFC 1327 mappings, but it is recommended in the 1988
To remain consistent with RFC 822, "Mail sent to that address is to
be routed to a person responsible for the site's mail system or to a
person with responsibility for general site operation." .
3.1. Software Limitations
If software is unable to support this requirement, it should be
upgraded. X.400 software developers are strongly encouraged and
requested to support forwarding mail to a centralized postmaster
mailbox in products.
It may be possible to support forwarding postmaster mail to a central
mailbox in software packages which do not explicitly support it by
applying work-around solutions. For example, some packages support
creating a mailing list for "postmaster" which has one entry that
points to the desired centralized postmaster mailbox. Alternatively,
it may be possible to support a postmaster address using the X.400
Autoforwarding feature. The software package may also support
rewriting the address in some other way.
This document is a product of discussion and comments from the IETF
OSI X.400 Operations Working Group. Helpful input was also received
from the European MHS Managers. Special thanks to Marko Kaittola and
Erik Lawaetz for good criticism and helpful discussion.
Security issues are not discussed in this memo.
5. Author's Address
Computer Sciences Department
University of Wisconsin-Madison
1210 West Dayton Street
Madison, WI 53706 USA
X.400: S=Cargille; O=UW-Madison; OU1=cs; PRMD=xnren; ADMD= ; C=us;
Phone: +1 (608) 262-5084
Fax: +1 (608) 262-9777
 Crocker, D., "Standard of the Format of ARPA Internet Text
Messages", STD 11, RFC 822, UDEL, August 1982.
 Braden, R., "Requirements for Internet Hosts -- Application and
Support", STD 3, RFC 1123, USC/Information Sciences Institute,
 CCITT, "CCITT Recommendations X.400", Message Handling Systems:
System Model--Service Elements, 1984.
 CCITT/ISO, "CCITT Recommendations X.400/ ISO IS 10021-1", Message
Handling: System and Service Overview, December 1988.
 Kille, S., "Mapping between X.400(1988) / ISO 10021 and RFC 822",
RFC 1327, University College London, May 1992.
 Hagens, R. and A. Hansen, "Operational Requirements for X.400
Management Domains in the GO-MHS Community," ANS, UNINETT, RFC
1649, July 1994.
 U.S. Department of Commerce, National Institute of Standards and
Technology, Stable Implementation Agreements for Open Systems
Interconnection Protocols, Version 7, Edition 1, Special
Publication 500-214, December 1993.
 Minutes, Cosine MHS Managers Meeting, June 1992, (unpublished).
 Crocker, D., "Standard of the Format of ARPA Internet Text
Messages", STD 11, RFC 822, UDEL, Pg. 33, August 1982.