RFC 1664 (rfc1664) - Page 2 of 23
Using the Internet DNS to Distribute RFC1327 Mail Address Mapping Tables
Alternative Format: Original Text Document
RFC 1664 Internet DNS for Mail Mapping Tables August 1994 and systems using the RFC 822 mail protocol, or protocols derived from RFC 822. That document addresses conversion of services, addresses, message envelopes, and message bodies between the two mail systems. This document is concerned with one aspect of RFC 1327: the mechanism for mapping between X.400 O/R addresses and RFC 822 domain names. As described in Appendix F of RFC 1327, implementation of the mappings requires a database which maps between X.400 O/R addresses and domain names, and this database is statically defined. This approach requires many efforts to maintain the correct mapping: all the gateways need to get coherent tables to apply the same mappings, the conversion tables must be distributed among all the operational gateways, and also every update needs to be distributed. This static mechanism requires quite a long time to be spent modifying and distributing the information, putting heavy constraints on the time schedule of every update. In fact it does not appear efficient compared to the Internet Domain Name Service (DNS). More over it does not look feasible to distribute the database to a large number of other useful applications, like local address converters, e-mail User Agents or any other tool requiring the mapping rules to produce correct results. A first proposal to use the Internet DNS to store, retrieve and maintain those mappings was introduced by two of the authors (B. Cole and R. Hagens) adopting two new DNS resource record (RR) types: TO- X400 and TO-822. This new proposal adopts a more complete strategy, and requires one new RR only. The distribution of the RFC 1327 mapping rules via DNS is in fact an important service for the whole Internet community: it completes the information given by MX resource record and it allows to produce clean addresses when messages are exchanged among the Internet RFC 822 world and the X.400 one (both Internet and Public X.400 service providers). A first experiment in using the DNS without expanding the current set of RR and using available ones was in the mean time deployed by some of the authors. The existing PTR resource records were used to store the mapping rules, and a new DNS tree was created under the ".it" top level domain. The result of the experiment was positive, and a few test applications ran under this provisional set up. This test was also very useful in order to define a possible migration strategy during the deployment of the new DNS containing the new RR. The Internet DNS nameservers wishing to provide this mapping information need in fact to be modified to support the new RR type, and in the real Internet, due to the large number of different implementations, this takes some time. The basic idea is to adopt a new DNS RR to store the mapping information. The RFC 822 to X.400 mapping rules (including the so Allocchio, Bonito, Cole, Giordano & Hagens
