Digest Format: Digest message format

Network Working Group                                          F. Wancho
Request for Comments: 1153                                          WSMR
                                                              April 1990


                         Digest Message Format

Status of this Memo

   This memo describes the de facto standard Digest Message Format.
   This is an elective experimental protocol.  Distribution of this memo
   is unlimited.

Background

   High traffic volume large mailing lists began to appear on the net in
   the mid-70s.  The moderators of those lists developed a digest
   message format to enclose several messages into one composite message
   for redistribution to the mailing list addressees.  This format
   reduces the mailer load in proportion to the number of messages
   contained within a digest message, and conserves network bandwidth by
   reducing the size of the headers of the enclosed messages.

   This RFC documents the digest message format so that others may
   follow this format in creating (digestifying) and separating
   (undigestifying) digest messages to maintain compatibility with the
   programs expecting this de facto standard.  Any editorial functions
   performed at the discretion of a digest moderator, such as discarding
   submissions, editing content to correct spelling and punctuation
   errors, inserting comments, and reformatting paragraphs to conform to
   width conventions are beyond the scope of this memo.

   This memo describes the de facto standard Digest Message Format.  It
   is not meant to supersede nor replace the generic message
   encapsulation format described in RFC 934.  It merely documents a
   particular message encapsulation format that existed well before RFC
   934 was published and continues to be the format of choice for digest
   messages.

Description

   A digest message is a conventional message consisting of a header and
   body conforming to RFC 822 as clarified in RFC 1123.  There is no
   fixed size.  Limitations may exist in intermediate mail gateways
   which restrict the size.  The typical digest size is 15,000
   characters.

   The header of a digest message should identify the digest in the
   Subject line by listname, the key word, Digest, the volume number
   (usually a sequential number either starting at 1 or the last two
   digits of the year and incremented by one starting with the first
   issue of the next calendar year), and an issue number starting at one
   for the first issue of a new calendar year.

   The body of a digest message must consist of a Preamble, one or more
   enclosed messages, and a Trailer.

   The Preamble usually contains a table of contents consisting of the
   subject line contents of the enclosed messages, usually indented or
   centered, and also may contain brief administrative or other
   announcements.

   The Preamble must be separated from the remainder of the message by a
   line of 70 hyphens followed by a blank line.

   Each enclosed message is a conventional message consisting of a
   header and body, separated by a blank line.  If they exist in the
   original message header, the following lines must be retained as-is
   in the reconstructed header: Date:, From:, To:, Cc:, Subject:,
   Message-ID:, and Keywords:, rearranged to appear in that order.
   Retaining the Summary: line is optional.  Lines include continuation
   lines as defined in the RFCs.  All other header lines should be
   discarded, especially Received lines.  All leading and trailing blank
   lines should be removed from the message body.  The message body may
   be scanned to replace with a blank the first character of any lines
   of exactly and only 30 hyphens.

   Each enclosed message must be separated from the the remainder of the
   digest message by a blank line before and after a line of 30 hyphens.

   The Trailer immediately follows the blank line of message separator
   following the last enclosed message.  The Trailer consists of two
   lines.  The first line must begin with the words, End of, followed by
   the listname a blank and the word Digest which is usually followed by
   volume and issue number on the same line.  The second and last line
   of the Trailer and the entire message is a line of asterisks serving
   to underline the line immediately above it.

Example

   The following example serves as a template for a digest message
   conforming to this memo.  It contains a header, and a body consisting
   of a Preamble, two enclosed messages, and a Trailer.  fqhn means
   Fully Qualified Host Name.  The Date: lines are examples only.

Date: ddd, dd mmm yy hh:mm:ss zzz
From: listname-REQUEST@fqhn
Reply-To: listname@fqhn
Subject: listname Digest Vyy #nn
To: listname@fqhn

listname Digest             ddd, dd mmm yy       Volume yy : Issue   nn

Today's Topics:
                          Message One Subject
                          Message Two Subject

Administrivia:

Messages from the list moderator or maintainer go here.

----------------------------------------------------------------------

Date: ddd, dd mmm yy hh:mm:ss zzz
From: Joe User <username@fqhn>
Subject: Message One Subject

This is the message body of the first message.

Joe

------------------------------

Date: ddd, dd mmm yy hh:mm:ss zzz
From: Jane User <username@fqhn>
Subject: Message Two Subject

This is the body of message two.

Jane

------------------------------

End of listname Digest Vyy Issue #nn
************************************

Security Considerations

   Security issues are not discussed in this memo.

Author's Address

   Frank J. Wancho
   USAISC-White Sands
   ASQNC-TWS-SS-C (F. Wancho, Building 1512)
   White Sands Missile Range, NM 88002-5506

   Phone: (505) 678-3009

   Email: WANCHO@WSMR-SIMTEL20.ARMY.MIL