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Introduction to the List Specification Headers for List Managers

By Grant Neufeld

Last update: August 2, 1998

The Problem

End users have difficulty understanding, remembering and using the wide variety of command systems used to access electronic mailing lists.

This results in headaches for both the users and list administrators as command messages are sent to the wrong addresses with the wrong syntax.

A Solution

Mail client software developers are implementing interface features to make mail list control easier for end users based on the List- Headers Fields [RFC 2369]. For example, a GUI mail client could potentially offer buttons to unsubscribe, subscribe, or get help with list commands (more options are currently under discussion).

With cooperation from client & server developers and list administrators, we can reduce the problem.

What You Need To Do

Implement, where appropriate, the List- header fields for your mailing lists. (The technical specifics of how to do this will depend on the list software you are using - please consult its manuals or tech support for specifics on adding header fields to your messages.)

These header fields provide the mail client software with a consistent method for determining the exact syntax for issuing commands through the use of well structured mailto (or other) URLs.

The two most important are the List-Help and List-Unsubscribe header fields, with List-Subscribe a close third.

Note that you do not have to implement all the header fields in order to use some of them. For example, private or hidden lists will probably want to leave out the List-Subscribe field.

Formatting Your URLs

It is crucial that your URLs be correctly formatted in order for the client software to be able to use them.

Note that, presently, variables are not supported in commands. This will affect list processors that require the user to put their name or email address (or whatever) in the text of a command.

When using a mailto URL, include the command to be sent to the control address by using the http form arguments format:


No spaces or other non-alphanumeric characters may be used in the fielddata. If you want to include them, they must be hex-encoded (with a percent sign '%' preceding the two-digit hexadecimal encoding).

The only two fieldnames you can use (as currently defined) are 'Subject' and 'Body'.

For more specific documentation, see the mailto URL scheme RFC 2368.


A mailing list named 'example' with a control address of 'listcontrol@server.mail' that takes commands in the body of the message. There is a web page for the list on the 'www.server.mail' server which provides instructions on accessing the list. The list archive is available through the mail server, an ftp server and the web server. The contact person for the list is 'grant'. The list would have the following header fields:

List-Help: <http://www.server.mail/example-list.html>, <mailto:listcontrol@server.mail?Body=help>
List-Unsubscribe: <mailto:listcontrol@server.mail?Body=unsubscribe%20example>
List-Subscribe: <mailto:listcontrol@server.mail?Body=subscribe%20example>
List-Post: <mailto:example@server.mail>
List-Owner: <mailto:grant@server.mail>
List-Archive: <mailto:listcontrol@server.mail?Body=Get%20Index%20example>, <ftp://ftp.server.mail/list/example/>, <http://http.server.mail/example/>

A mailing list named 'test-list' which uses the list address 'test-list@mail.test' as the control address and takes commands in the subject of the message. There is no web page or archive for the list, so a help mail request retrieves instructions on accessing the list. A human contact for the list can be reached through the 'listmom' address. The list would have the following header fields:

List-Help: <mailto:test-list@mail.test?Subject=help>
List-Unsubscribe: <mailto:test-list@mail.test?Subject=unsubscribe>
List-Subscribe: <mailto:test-list@mail.test?Subject=subscribe>
List-Post: <mailto:test-list@mail.test>
List-Owner: <mailto:listmom@mail.test>

A mailing list named 'web-list' which uses a web server interface on the www.mail.web server for all list commands. Commands may also be processed through the 'server' mail address. The human contact is the same as the postmaster for the mail server, so the List-Owner field is not needed. The list would have the following header fields:

List-Help: <http://www.mail.web/web-list.cgi>, <mailto:server@www.mail.web?Body=help>
List-Unsubscribe: <http://www.mail.web/web-list.cgi?action=unsubscribe>, <mailto:server@www.mail.web?Body=unsubscribe%20web-list>
List-Subscribe: <http://www.mail.web/web-list.cgi?action=subscribe>, <mailto:server@www.mail.web?Body=subscribe%20web-list>
List-Post: <mailto:web-list@www.mail.web>
List-Archive: <http://www.mail.web/web-list.cgi?action=archive>

This document is intended for redistribution on the internet.
Permission is granted to redistribute in whole or in part on the internet provided this complete copyright notice remains intact.
All other reproduction requires prior authorization from the author.

Copyright ©1997-1998 Grant Neufeld.
Nisto and are trademarks of Grant Neufeld.