RFC 1153

RFC 1153: Digest Message Format 💖

Author: Frank J. Wancho (WSMR) 🎀 Date: April 1990 📅 Category: elective experimental protocol 🧪 Obsoletes / Updates: nothing is listed in the title block 🦋 Network Working Group: Request for Comments: 1153 ✨

Status of this Memo 💅

okay so this memo describes the de facto standard Digest Message Format. it's an elective experimental protocol, and distribution of this memo is unlimited 🌸

Background 🌈

so high traffic, large mailing lists started showing up on the net in the mid-70s 🙈 the moderators of those lists came up with a digest message format that bundles several messages into one composite message for redistribution to the list addressees. this is lowkey genius because it reduces the mailer load in proportion to the number of messages inside a digest, and it saves network bandwidth by shrinking the headers of the enclosed messages 🫶

this RFC documents the format so that other people can follow it when they create (digestify) and separate (undigestify) digest messages. that keeps everything compatible with the programs that expect this de facto standard 💜

editorial stuff a digest moderator does at their discretion is not part of this memo. that covers discarding submissions, editing content to fix spelling and punctuation, inserting comments, and reformatting paragraphs to match width conventions 💅

this memo is not meant to supersede or replace the generic message encapsulation format described in RFC 934. it just documents one particular encapsulation format that was around well before RFC 934 was published, and it's still the format of choice for digest messages 👑

Description 🧚

a digest message is a conventional message made of a header and a body that conforms to RFC 822 as clarified in RFC 1123. there's no fixed size, though intermediate mail gateways may have limits. the typical digest size is 15,000 characters 🍓

the header should identify the digest in its Subject line. that means the listname, the key word Digest, the volume number (usually sequential, either starting at 1 or using the last two digits of the year and going up by one starting with the first issue of the next calendar year), and an issue number that starts at one for the first issue of a new calendar year ✨

the body must consist of a Preamble, one or more enclosed messages, and a Trailer 🎀

the Preamble usually has a table of contents made of the subject lines of the enclosed messages, usually indented or centered. it may also include brief administrative or other announcements 🦋

the Preamble must be separated from the rest of the message by a line of 70 hyphens followed by a blank line 🌸

each enclosed message is a conventional message with a header and body, separated by a blank line. if they exist in the original message header, these lines must be kept as-is in the rebuilt header, rearranged to appear in this order: Date:, From:, To:, Cc:, Subject:, Message-ID:, and Keywords:. keeping the Summary: line is optional. lines include continuation lines as defined in the RFCs. every other header line should be thrown out, 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 made of exactly and only 30 hyphens 🔥

each enclosed message must be separated from 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 the message separator that comes after the last enclosed message. the Trailer is two lines long. the first line must begin with the words End of, followed by the listname, a blank, and the word Digest. that's usually followed by the volume and issue number on the same line. the second and last line of the Trailer, and the last line of the entire message, is a line of asterisks that underlines the line right above it 😭

Example 💜

this example is a template for a digest message that follows this memo. it has a header, plus a body made 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. no cap, implementers should keep that in mind 👀

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