Password-protected mailing lists

Mailing lists may be set up to require a password in order to post. For mailing lists defined via the aliases file or alias database, the password value (or list of values) is specified via the &#x5b;PASSWORD&#x5d;  mailing list named parameter; see  Alias file named parameters. In Unified Configuration, the analogous setting is the  alias option. For mailing lists defined in LDAP, the password value (or list of values) is specified  via the   attribute (or more precisely,  whatever attribute is specified by the    MTA option).

In order for a message to be posted to the list, the MTA will then require that the message include, on an Approved: header line, one of  the authorizing passwords. During the mailing list expansion process, the MTA will remove that password value from the Approved: header line,  and indeed remove the entire Approved: header line if that was the only  value present. (In the case of multiple values, all passwords for a list will be removed. So in the case of nested lists, make sure that  the list password sets for the different lists are disjoint.) So note  that the Approved: header line value that allowed the message to be  posted will not be exposed in the actual posted message. Members of the list will not see the password. The group of users who can post (who know and use the password) can be a subset, or even a  completely separate group of users.

Note that since a single mailing list can have multiple allowed passwords, it is possible to assign a separate password to each allowed  poster.

Since mailing lists may be nested (one mailing list may be subscribed as a member of another mailing list), and since mailing list may have  its own password(s), an Approved: header line may contain multiple,  comma-separated values.

Password-protected mailing lists automatically get deferred expansion of membership.

See also:
 * Alias file named parameters
 * alias_password Option
 * ldap_auth_password MTA Option
 * ldap_auth_policy MTA Option
 * Process and reprocess channels