RFC 1648

RFC 1648: Postmaster Convention for X.400 Operations 💌

Okay bestie, here's the tea on this one 🫶

• Author: A. Cargille, University of Wisconsin
• Category: Standards Track
• Date: July 1994
• Obsoletes / Updates: the title block doesn't list either one

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Status of this Memo ✨

okay so this doc is an Internet standards track protocol for the whole Internet community 🌐, and it's literally asking everyone for discussion and suggestions so it can get even better 💬. For the current standardization state and status of this protocol, go check the current edition of "Internet Official Protocol Standards" (STD 1) 📜. Distribution of this memo is unlimited 🦋.

Abstract 🎀

okay so STD 11 (RFC 822 [1]) and STD 3 (RFC 1123 [2], the Host Requirements) both say the email address "postmaster" has to be supported at all hosts 🙈. This paper takes that idea and extends it to X.400 mail domains that have registered RFC 1327 mapping rules. Those domains end up with normal-looking RFC822-style addresses, so they're giving main character energy 💅.

1. Postmaster Convention in RFC822 💌

Running a reliable, large-scale email network takes teamwork from tons of mail managers and system administrators 🤝. As RFC 822 [1] points out, mail or system managers often need to reach a responsible person at a remote host without knowing any specific user name or address there 🕵️‍♀️. That's why both RFC 822 and the Internet Host Requirements [2] say the address "postmaster" must be supported at every Internet host 💖.

2. Postmaster Convention and X.400 🌸

But RFC 822 isn't the only email protocol out here 👀. Some Internet sites also run X.400 (1984) [3] and X.400 (1988) [4]. RFC 1327 explains how to map between X.400 and RFC 822 addresses [5]. When those mapping rules are used, addresses map cleanly between the two, and honestly it's iconic: you can't tell by looking at an 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 called the "Global Open MHS Community" (GO-MHS) [6] 🧚. A lot of mail domains in GO-MHS have registered RFC 1327 mapping rules. So users in those domains have RFC 822-style email addresses, and those domains are basically a logical extension of the RFC 822 Internet 🌈. Once again, you can't tell from a user's address whether they get RFC 822 mail or X.400 mail. Total mystery, no cap 🙈.

Since these addresses look like standard RFC 822 addresses, mail managers, mailing list managers, host administrators, and users all expect to be able to just send mail to "postmaster@domain" and have it reach a responsible party 📬. When an RFC 1327 mapping rule exists, the X.400 address element that matches the left-hand-side "postmaster" is "Surname=Postmaster" (in both 1984 and 1988). But the X.400 protocols, the North America X.400 Implementor's Agreements [7], and the other regional X.400 implementor's agreements don't require that "Surname=Postmaster" and "CommonName=Postmaster" be supported. (Supporting these addresses is recommended in X.400 (1988).) Lowkey a plot twist 😭.

So for mapped X.400 domains that don't support the postmaster address(es), user@some.place.zz might be valid while mail to postmaster@some.place.zz fails. That's so frustrating for remote admins and users 💀, and it can stop operational problems from being reported and fixed 🛠️. The seamless link between the Internet RFC 822 mail world and the mapped X.400 domain hasn't been achieved yet 🥺.

The X.400 mail managers in the Cosine MHS Project talked about this problem at a meeting in June 1992 [8] 🗣️. They agreed the postmaster address should be supported at any level of the address hierarchy where there are user addresses 🌳. But the group only required postmaster support down to certain levels of the O/R Address tree. That fixed part of the problem, but not all of it 😤. A more complete solution is required ✨.

3. Proposed Solution 🎀

To fully achieve that seamless integration for email domains with RFC 1327 mapping rules, 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.

In X.400 terms: for every X.400 domain with an RFC 1327 mapping rule, if any address of this form is valid:

Surname=User; <Other X.400 Address Elements>

then this address must also be valid:

Surname=Postmaster; <Same X.400 Address Elements>

If the X.400 system is running X.400(1988), then this address must also be supported:

CommonName=Postmaster; <Same X.400 Address Elements>

(Note that CommonName=Postmaster won't be generated by RFC 1327 mappings, but the 1988 X.400 standard recommends it 📝.)

To stay 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." [9] 🧡

3.1. Software Limitations 🛠️

If software can't 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 their products 💅.

It may be possible to forward postmaster mail to a central mailbox in software packages that don't explicitly support it, using work-around solutions 🧩. For example, some packages let you create a mailing list for "postmaster" with one entry that points to the desired centralized postmaster mailbox. Another option: 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 🪄.

4. Acknowledgements 💜

This document came out of discussion and comments from the IETF OSI X.400 Operations Working Group 🫶. Helpful input also came from the European MHS Managers 🇪🇺. Special thanks to Marko Kaittola and Erik Lawaetz for good criticism and helpful discussion 🙏.

Security Considerations 🚨

Security issues are not discussed in this memo. 😱 Not one word. Proceed with caution, bestie 💀.

5. Author's Address 🏡

Allan Cargille
Associate Researcher
Computer Sciences Department
University of Wisconsin-Madison
1210 West Dayton Street
Madison, WI   53706   USA

Internet: cargille@cs.wisc.edu
X.400: S=Cargille; O=UW-Madison; OU1=cs; PRMD=xnren; ADMD= ; C=us;

Phone: +1 (608) 262-5084
Fax:   +1 (608) 262-9777

6. References 📚

• [1] Crocker, D., "Standard of the Format of ARPA Internet Text Messages", STD 11, RFC 822, UDEL, August 1982.
• [2] Braden, R., "Requirements for Internet Hosts -- Application and Support", STD 3, RFC 1123, USC/Information Sciences Institute, October 1989.
• [3] CCITT, "CCITT Recommendations X.400", Message Handling Systems: System Model--Service Elements, 1984.
• [4] CCITT/ISO, "CCITT Recommendations X.400/ ISO IS 10021-1", Message Handling: System and Service Overview, December 1988.
• [5] Kille, S., "Mapping between X.400(1988) / ISO 10021 and RFC 822", RFC 1327, University College London, May 1992.
• [6] Hagens, R. and A. Hansen, "Operational Requirements for X.400 Management Domains in the GO-MHS Community," ANS, UNINETT, RFC 1649, July 1994.
• [7] 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.
• [8] Minutes, Cosine MHS Managers Meeting, June 1992, (unpublished).
• [9] Crocker, D., "Standard of the Format of ARPA Internet Text Messages", STD 11, RFC 822, UDEL, Pg. 33, August 1982.