RFC 1428 (rfc1428) - Page 1 of 6

Transition of Internet Mail from Just-Send-8 to 8bit-SMTP/MIME

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Network Working Group                                       G. Vaudreuil
Request for Comments: 1428                                          CNRI
                                                           February 1993


                   Transition of Internet Mail from
                              Just-Send-8
                           to 8bit-SMTP/MIME

Status of this Memo

   This RFC provides information for the Internet community.  It does
   not specify an Internet standard.  Distribution of this memo is
   unlimited.

Abstract

   Protocols for extending SMTP to pass 8bit characters have been
   defined [3] [4]. These protocols require that messages transported by
   the extended SMTP are to be encoded in MIME [1] [2].  Before work
   began on these protocols, several SMTP implementations adopted ad-hoc
   mechanisms for sending 8bit data. It is desirable for the extended
   SMTP environment and these ad hoc mechanisms interoperate.  This
   document outlines the problems in this environment and an approach to
   minimizing the cost of transition from current usage of non-MIME 8bit
   messages to MIME.

1. Terminology

   RFC 821 defines a 7bit transport.  A transport agent which does not
   clear the high order bit upon receipt of octets with this bit set in
   SMTP messages is called 8 bit transparent in this document. An
   implementation of the general SMTP Extensions document [3] and the
   8bit extensions protocol [4] which passes MIME messages using all 8
   bits of an octet is called 8bit ESMTP.  An implementation of extended
   SMTP which does not accept 8bit characters is called 7bit ESMTP.  A
   gateway is defined to be a transport agent with User Agent authority
   to alter or convert the content of a message.

2. The Problem

   SMTP as defined in RFC 821 limits the sending of Internet Mail to
   US-ASCII [5] characters.  As the Internet has grown to include non-
   English correspondents, the need to communicate with character sets
   other than US-ASCII has prompted many vendors and users to extend
   SMTP or RFC 822 to use non-ASCII character sets.  Common approaches
   are to send 7 bit national variant ISO 646 character sets over
   current RFC 822/SMTP, to extend SMTP and RFC 822 to use 8bit ISO 8859



Vaudreuil
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