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RFC 1648

               Postmaster Convention for X.400 Operations

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 [1], 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 [2]
   require that the address "postmaster" be supported at every Internet
   host.

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) [3]
   and X.400 (1988) [4] email protocols.  RFC 1327 specifies how to map
   between X.400 and RFC 822 addresses [5].  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) [6].  Many mail
   domains in the GO-MHS Community have registered RFC 1327 mapping
   rules.  Therefore, users in those domains have RFC 822-style email



Cargille                                                        [Page 1]

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 [7], 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 "user@some.place.zz" might be valid, yet mail to the corresponding address "postmaster@some.place.zz" 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 [8]. 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 required. 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> Cargille [Page 2]
RFC 1648 X.400 Postmaster Convention July 1994 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 X.400 standard). 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." [9]. 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. 4. Acknowledgements 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 Considerations Security issues are not discussed in this memo. Cargille [Page 3]
RFC 1648 X.400 Postmaster Convention July 1994 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.



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