RFC 1505 (rfc1505) - Page 3 of 36

Encoding Header Field for Internet Messages

RFC 1505                 Encoding Header Field               August 1993


1.  Introduction

   STD 11, RFC 822 [2] defines an electronic mail message to consist of
   two parts, the message header and the message body, separated by a
   blank line.

   The Encoding header field permits the message body itself to be
   further broken up into parts, each part also separated from the next
   by a blank line.  Thus, conceptually, a message has a header part,
   followed by one or more body parts, all separated by apparently blank
   lines.  Each body part has an encoding type.  The default (no
   Encoding field in the header) is a one part message body of type
   "Text".

   The purpose of Encoding is to be descriptive of the content of a mail
   message without placing constraints on the content or requiring
   additional structure to appear in the body of the message that will
   interfere with other processing.

   A similar message format is used in the network news facility, and
   posted articles are often transferred by gateways between news and
   mail.  The Encoding field is perhaps even more useful in news, where
   articles often are uuencoded or shar'd, and have a number of
   different nested encodings of graphics images and so forth.  In news
   in particular, the Encoding header keeps the structural information
   within the (usually concealed) article header, without affecting the
   visual presentation by simple news-reading software.

2.  The Encoding Field

   The Encoding field consists of one or more subfields, separated by
   commas.  Each subfield corresponds to a part of the message, in the
   order of that part's appearance.  A subfield consists of a line count
   and a keyword or a series of nested keywords defining the encoding.
   The line count is optional in the last subfield.

2.1  Format of the Encoding Field

   The format of the Encoding field is:

        [   [  ]* ,  ]*
                [  ]  [  ]*

        where:

            := a decimal integer
          := a single alphanumeric token starting with an alpha




Costanzo, Robinson & Ullmann