RFC 2049 (rfc2049) - Page 3 of 24

Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples

RFC 2049                    MIME Conformance               November 1996


   A mail user agent that is MIME-conformant MUST:

    (1)   Always generate a "MIME-Version: 1.0" header field in
          any message it creates.

    (2)   Recognize the Content-Transfer-Encoding header field
          and decode all received data encoded by either quoted-
          printable or base64 implementations.  The identity
          transformations 7bit, 8bit, and binary must also be
          recognized.

          Any non-7bit data that is sent without encoding must be
          properly labelled with a content-transfer-encoding of
          8bit or binary, as appropriate.  If the underlying
          transport does not support 8bit or binary (as SMTP
          [RFC-821] does not), the sender is required to both
          encode and label data using an appropriate Content-
          Transfer-Encoding such as quoted-printable or base64.

    (3)   Must treat any unrecognized Content-Transfer-Encoding
          as if it had a Content-Type of "application/octet-
          stream", regardless of whether or not the actual
          Content-Type is recognized.

    (4)   Recognize and interpret the Content-Type header field,
          and avoid showing users raw data with a Content-Type
          field other than text.  Implementations  must be able
          to send at least text/plain messages, with the
          character set specified with the charset parameter if
          it is not US-ASCII.

    (5)   Ignore any content type parameters whose names they do
          not recognize.

    (6)   Explicitly handle the following media type values, to
          at least the following extents:

          Text:

            -- Recognize and display "text" mail with the
            character set "US-ASCII."

            -- Recognize other character sets at least to the
            extent of being able to inform the user about what
            character set the message uses.






Freed & Borenstein          Standards Track