RFC 2049 (rfc2049) - Page 3 of 24
Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples
Alternative Format: Original Text Document
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