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.
