RFC 1428 (rfc1428) - Page 2 of 6

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

RFC 1428              Transition to 8bit-SMTP/MIME         February 1993


   character sets, and to use proprietary PC character sets.

   A third approach is used for Japanese mail.  Japanese characters are
   represented by pairs of octets with the high order bit cleared.
   Switching between 14 bit character sets and 7 bit character sets is
   indicated within the message by ISO 2022 escape sequences.

   So long as these implementations can communicate without intermediate
   transformations and have a loose private agreement on the use of a
   specific character set without tagging, basic mail service can be
   provided.

   In the transition to the negotiated 8bit ESMTP/MIME environment, it
   is important that mail sent by a currently non-conforming user can be
   read by another non-conforming user.  This existing functionality is
   reduced by conversion from 8bit text to text encoded in unreadable
   Base-64 or "garbled" text encoded in quoted printable.

   There are several interesting non-interoperable cases that currently
   exist in non US-ASCII mail and several new ones likely to emerge in a
   transition to 8bit/MIME.  Below is a listing of the transition-to-
   mime cases.  Only solutions to (4) in the context of a translating
   gateway are discussed in this memo.

                \ Receiver
                  \    7bit     8bit          MIME/
             Sender \| only   | transparent | ESMTP
           ----------------------------------------
           7bit only |  (1)   |    (1)      | (1)
           ----------------------------------------
    8bit transparent |  (2)   |    (3)      | (4)
           ----------------------------------------
          MIME/ESMTP |  (5)   |    (5)      | (6)


   (1) 7Bit non-MIME sender to 7bit, MIME, or 8bit transparent receiver

      This will continue to work unchanged with nationally varient ISO
      646 or ISO 2022 character set shifting if an external "out of
      band" agreement exists between the sender and the receiver.  A
      7bit to 8bit/ESMTP gateway need not alter the content of this
      message.

   (2) 8bit sender to 7bit non-MIME receiver

      The receiver will receive bit-stripped mail which results in the
      mis-interpretation of the data and the wrong character being
      displayed or printed.  Mail sent using languages where most



Vaudreuil