Implications of MIME for Internet Mail Gateways (RFC1344)

Network Working Group N. Borenstein, Bellcore Request for Comments: 1344 June 1992

Implications of MIME for Internet Mail Gateways

Status of This Memo

This is an informational memo for the Internet community, and requests discussion and suggestions for improvements. This memo does not specify an Internet standard. Distribution of this memo is unlimited.

Abstract

The recent development of MIME (Multipurpose Internet Mail Extensions) offers a wide range of new opportunities for electronic mail system systems. Most of these opportunites are relevant only to user agents, the programs that interact with human users when they send and receive mail. However, some opportunities are also opened up for mail transport systems. While MIME was carefully designed so that it does not require any changes to Internet electronic message transport facilities, there are several ways in which message transport systems may want to take advantage of MIME. These opportunities are the subject of this memo.

Background -- The MIME Format

Recently, a new standardized format has been defined for enhanced electronic mail messages on the Internet. This format, known as MIME, permits messages to include, in a standardized manner, non-ASCII text, images, audio, and a variety of other kinds of interesting data.

The MIME effort was explicitly focused on requiring absolutely no changes at the message transport level. Because of this fact, MIME-format mail runs transparently on all known Internet or Internet-style mail systems. This means that those concerned solely with the maintenance and development of message transport services can safely ignore MIME completely, if they so choose.

However, the fact that MIME can be ignored, for the purpose of message transport, does not necessarily mean that it should be ignored. In particular, MIME offers several features that should be of interest to those responsible for message transport services. By exploiting these features, transport systems can provide certain additional kinds of service that are currently unavailable, and can alleviate a few existing problems.

The remainder of this document is an attempt to briefly point out and summarize some important ways in which MIME

Borenstein [Page 1]

RFC 1344 MIME and Mail Gateways June 1992

may be of use for message transport systems. This document makes no attempt to present a complete technical description of MIME, however. For that, the reader is refered to the MIME document itself [RFC-1341].

Mail Transport and Gateway Services: A Key Distinction

Before implementing any of the mechanisms discussed in this memo, one should be familiar with the distinction between mail transport service and mail gateway service. Basically, mail transport software is responsible for moving a message within a homogeneous electronic mail service network. Mail gateways, on the other hand, exchange mail between two significantly different mail environments, including via non-electronic services, such as postal...