RFC 2047 (rfc2047) - Page 2 of 15

MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text

RFC 2047               Message Header Extensions           November 1996


   Other documents in this series include:

   + RFC 2045, which specifies the various headers used to describe
     the structure of MIME messages.

   + RFC 2046, which defines the general structure of the MIME media
     typing system and defines an initial set of media types,

   + RFC 2048, which specifies various IANA registration procedures
     for MIME-related facilities, and

   + RFC 2049, which describes MIME conformance criteria and
     provides some illustrative examples of MIME message formats,
     acknowledgements, and the bibliography.

   These documents are revisions of RFCs 1521, 1522, and 1590, which
   themselves were revisions of RFCs 1341 and 1342.  An appendix in RFC
   2049 describes differences and changes from previous versions.

1. Introduction

   RFC 2045 describes a mechanism for denoting textual body parts which
   are coded in various character sets, as well as methods for encoding
   such body parts as sequences of printable US-ASCII characters.  This
   memo describes similar techniques to allow the encoding of non-ASCII
   text in various portions of a RFC 822 [2] message header, in a manner
   which is unlikely to confuse existing message handling software.

   Like the encoding techniques described in RFC 2045, the techniques
   outlined here were designed to allow the use of non-ASCII characters
   in message headers in a way which is unlikely to be disturbed by the
   quirks of existing Internet mail handling programs.  In particular,
   some mail relaying programs are known to (a) delete some message
   header fields while retaining others, (b) rearrange the order of
   addresses in To or Cc fields, (c) rearrange the (vertical) order of
   header fields, and/or (d) "wrap" message headers at different places
   than those in the original message.  In addition, some mail reading
   programs are known to have difficulty correctly parsing message
   headers which, while legal according to RFC 822, make use of
   backslash-quoting to "hide" special characters such as "RFC 822 headers, to "break" these programs would cause
   severe operational problems for the Internet mail system.  The
   extensions described in this memo therefore do not rely on little-
   used features of RFC 822.



Moore                       Standards Track