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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
Wancho [Page 1]
RFC 1153 Digest Message Format April 1990
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.
Wancho [Page 2]
RFC 1153 Digest Message Format April 1990
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