MIME (Multipurpose Internet Mail Extensions): Mechanisms for Specifying and Describing the Format of Internet Message Bodies
RFC 1341

Document Type RFC - Proposed Standard (June 1992; No errata)
Obsoleted by RFC 1521
Last updated 2013-03-02
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Network Working Group               N. Borenstein, Bellcore
            Request for Comments: 1341               N. Freed, Innosoft
                                                              June 1992

                   MIME  (Multipurpose Internet Mail Extensions):

                      Mechanisms for Specifying and Describing
                       the Format of Internet Message Bodies

          Status of this Memo

            This RFC specifies an IAB standards track protocol  for  the
            Internet  community, and requests discussion and suggestions
            for improvements.  Please refer to the  current  edition  of
            the    "IAB    Official    Protocol   Standards"   for   the
            standardization  state  and   status   of   this   protocol.
            Distribution of this memo is unlimited.

          Abstract

            RFC 822 defines  a  message  representation  protocol  which
            specifies  considerable  detail  about  message headers, but
            which leaves the message content, or message body,  as  flat
            ASCII  text.   This document redefines the format of message
            bodies to allow multi-part textual and  non-textual  message
            bodies  to  be  represented  and  exchanged  without loss of
            information.   This is based on earlier work  documented  in
            RFC  934  and  RFC  1049, but extends and revises that work.
            Because RFC 822 said so little about  message  bodies,  this
            document  is  largely  orthogonal to (rather than a revision
            of) RFC 822.

            In  particular,  this  document  is  designed   to   provide
            facilities  to include multiple objects in a single message,
            to represent body text in  character  sets  other  than  US-
            ASCII,  to  represent formatted multi-font text messages, to
            represent non-textual material  such  as  images  and  audio
            fragments,  and  generally  to  facilitate  later extensions
            defining new types of Internet mail for use  by  cooperating
            mail agents.

            This document does NOT extend Internet mail header fields to
            permit  anything  other  than  US-ASCII  text  data.   It is
            recognized that such extensions are necessary, and they  are
            the subject of a companion document [RFC -1342].

            A table of contents appears at the end of this document.

            Borenstein & Freed                                  [Page i]




            1    Introduction

            Since its publication in 1982, RFC 822 [RFC-822] has defined
            the   standard  format  of  textual  mail  messages  on  the
            Internet.  Its success has been such that the RFC 822 format
            has  been  adopted,  wholly  or  partially,  well beyond the
            confines of the Internet and  the  Internet  SMTP  transport
            defined  by RFC 821 [RFC-821].  As the format has seen wider
            use,  a  number  of  limitations  have  proven  increasingly
            restrictive for the user community.

            RFC 822 was intended to specify a format for text  messages.
            As such, non-text messages, such as multimedia messages that
            might include audio or images,  are  simply  not  mentioned.
            Even in the case of text, however, RFC 822 is inadequate for
            the needs of mail users whose languages require the  use  of
            character  sets  richer  than US ASCII [US-ASCII]. Since RFC
            822 does not specify mechanisms for mail  containing  audio,
            video,  Asian  language  text, or even text in most European
            languages, additional specifications are needed

            One of the notable limitations of  RFC  821/822  based  mail
            systems  is  the  fact  that  they  limit  the  contents  of
            electronic  mail  messages  to  relatively  short  lines  of
            seven-bit  ASCII.   This  forces  users  to convert any non-
            textual data that they may wish to send into seven-bit bytes
            representable  as printable ASCII characters before invoking
            a local mail UA (User Agent,  a  program  with  which  human
            users  send  and  receive  mail). Examples of such encodings
            currently used in the  Internet  include  pure  hexadecimal,
            uuencode,  the  3-in-4 base 64 scheme specified in RFC 1113,
            the Andrew Toolkit Representation [ATK], and many others.

            The limitations of RFC 822 mail become even more apparent as
            gateways  are  designed  to  allow  for the exchange of mail
            messages between RFC 822 hosts and X.400 hosts. X.400 [X400]
            specifies  mechanisms  for the inclusion of non-textual body
            parts  within  electronic  mail   messages.    The   current
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