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Guidelines to the List - Header Fields for Server Application Authors

By Grant Neufeld

Last update: August 2, 1998

The List- header fields provide you with a standard method by which you can consistently describe electronic mailing list command syntax so that client applications can implement an interface to make list access easier for users.

Header Field Requirements

There are presently six header fields which should be supported.

Using URLs in List Header Fields

Currently, each header field is defined to contain a comma-separated list of URLs. The individual URLs are to be enclosed in angle brackets <>. You must follow the URL standard for character encoding (spaces and other special characters must be %-hex encoded).

The URLs may be any valid URL, using any valid protocol. Whenever possible, a mailto URL should be included. If you want to use other protocols, include them in addition to a mailto URL.

The URLs specified in a field will have precedence from left to right, so that a client application will try to use the leftmost URL that it understands.

The mailto URL scheme is required to describe mail commands which use the Subject field or the body of the message.

The Header Fields

See the explanation above of the structure of the content for these fields.


A general purpose URL for the user to get information and help with the list, and possibly for web-controlled subscription management.


Unsubscribe (remove, off) from the list.


Subscribe (join, on) to the list.


The address to send messages to be posted/forwarded to the list.

There is a special case for the field. It may contain the single word "NO" which is used to indicate that the list does not accept postings.


Contact address for a human list administrator (list-manager, list-mom). It's not necessary to include this if it is the same as the postmaster for the list's domain.


URL for accessing archives of past list messages.


List-Unsubscribe: <>
  List-Subscribe: <>
       List-Help: <>, <>
       List-Post: <>
      List-Owner: <> (contact for administrative questions)
    List-Archive: <>


Mail list processors should not allow any user-originated list header fields to pass through to their lists, lest they confuse the user and have the potential to create security problems.

Implementation Guidelines

The List header fields should be automatically generatedby the server application as mailto URLs. The list administrator should, however, have an opportunity to override the default URL, substituting - or prepending - their own (such as a pointer to a web page).

The list administrator should be able to turn individual header fields on or off on a per-list basis.

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.