Network Working Group H. Alvestrand Request for Comments: 1496 SINTEF DELAB Updates: 1328 J. Romaguera NetConsult AG K. Jordan Control Data Systems, Inc. August 1993
Rules for Downgrading Messages from X.400/88 to X.400/84 When MIME Content-Types are Present in the Messages
Status of this Memo
This RFC specifies an IAB standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Interworking between X.400(88) and MIME is achieved by , which complements RFC-1327 , which in turn specifies the interworking between X.400(88) and RFC-822 based mail.
Interworking between X.400(88) and X.400 (84) is achieved by RFC-1328 . That document does not describe what to do in the case where body parts arrive at the gateway that cannot be adequately represented in the X.400(84) system.
This document describes how RFC-1328 must be modified in order to provide adequate support for the scenarios:
The approach is to imagine that the connection X.400(84) <-> SMTP(MIME) never happens. This, of course, is an illusion, but can be a very useful illusion.
All mail will therefore go on one of the paths
X.400(84) -> X.400(88) -> SMTP(MIME)
SMTP(MIME) -> X.400(88) -> X.400(84)
when it goes between a MIME user and an X.400(84) user.
The approach at the interface between X.400(88) and X.400(84) is:
o Convert what you can
o Encapsulate what you have to
o Never drop a message
Of course, for X.400/88 body parts that are already defined in X.400/84, no downgrading should be done. In particular, multi-body messages should remain multi-body messages, IA5 messages including IA5 messages encoded as Extended Body Parts) should remain IA5 messages, and G3Fax messages should remain G3Fax messages.
- People with X.400(84) readers who have the ability to save messages to file will now be able to save MIME multimedia messages
- People who can use features like the "Mailcaps" file to identify what to do about a bodypart can now grab implementations of MIME that can run as subprograms and achieve at least some multimedia functionality
 Borenstein, N, and N. Freed, "MIME: Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1341, Bellcore, Innosoft, June 1992.
 Hardcastle-Kille, S., "Mapping between X.400(1988) / ISO 10021 and RFC-822", RFC 1327, University College London, May 1992.
 Hardcastle-Kille, S., "X.400 1988 to 1984 downgrading", RFC 1328, University College London, May 1992.
 Alvestrand, H., Kille, S., Miles, R., Rose, M., and S. Thompson, "Mapping between X.400 and RFC-822 Message Bodies", RFC 1494, SINTEF DELAB, ISODE Consortium, Soft*Switch, Inc, Dover Beach Consulting, Inc., Soft*Switch, Inc., August 1993.