RFC 2047 (rfc2047) - Page 2 of 15
MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text
Alternative Format: Original Text Document
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