RFC 1341 (rfc1341) - Page 2 of 77

MIME (Multipurpose Internet Mail Extensions): Mechanisms for Specifying and Describing the Format of Internet Message Bodies

            RFC 1341MIME: Multipurpose Internet Mail ExtensionsJune 1992


            This document describes several mechanisms that  combine  to
            solve most of these problems without introducing any serious
            incompatibilities with the existing world of RFC  822  mail.
            In particular, it describes:

            1.  A MIME-Version header field, which uses a version number
                 to  declare  a  message  to  be  conformant  with  this
                 specification and  allows  mail  processing  agents  to
                 distinguish  between  such messages and those generated
                 by older or non-conformant software, which is  presumed
                 to lack such a field.

            2.  A Content-Type header field, generalized from  RFC  1049
                 [RFC-1049],  which  can be used to specify the type and
                 subtype of data in the body of a message and  to  fully
                 specify  the  native  representation (encoding) of such
                 data.

                 2.a.  A "text" Content-Type value, which can be used to
                      represent  textual  information  in  a  number  of
                      character  sets  and  formatted  text  description
                      languages in a standardized manner.

                 2.b.  A "multipart" Content-Type value,  which  can  be
                      used  to  combine  several body parts, possibly of
                      differing types of data, into a single message.

                 2.c.  An "application" Content-Type value, which can be
                      used  to transmit application data or binary data,
                      and hence,  among  other  uses,  to  implement  an
                      electronic mail file transfer service.

                 2.d.  A "message" Content-Type value, for encapsulating
                      a mail message.

                 2.e  An "image"  Content-Type value,  for  transmitting
                      still image (picture) data.

                 2.f.  An "audio"  Content-Type value, for  transmitting
                      audio or voice data.

                 2.g.  A "video"  Content-Type value,  for  transmitting
                      video or moving image data, possibly with audio as
                      part of the composite video data format.

            3.  A Content-Transfer-Encoding header field, which  can  be
                 used  to specify an auxiliary encoding that was applied
                 to the data in order to allow it to pass  through  mail
                 transport  mechanisms  which may have data or character
                 set limitations.

            4.  Two optional header fields that can be used  to  further
                 describe the data in a message body, the Content-ID and
                 Content-Description header fields.



            Borenstein & Freed