PMDF provides several mechanisms for forwarding mail. The method appropriate to a task at hand depends upon the scope of the forwarding:

• Forwarding mail for selected users. To forward mail for selected users, it is best to use aliases. You may also use aliases to accept mail for a non-existent user and forward it on to one or more real users. See Section 3.5.1.
• Forwarding mail to a list of users. Aliases are also used to create mailing lists. See Section 4.1; Section 4.1.3 contains a mailing list example.
• Forwarding mail for selected users in other than the local domain. To forward mail for selected users in an arbitrary domain (a domain other than the local channel name), use of the directory channel is often appropriate. See Section 3.2.
• Forwarding all mail for a given host to another host. In this case there are several approaches. The most efficient method requires that you be able to blindly change user@old-host into user@new-host without any conflict in user names; i.e., not have to worry that the username "user" on old-host conflicts with a different person on new-host who has the same username. When this is the case, simple rewrite rules in the PMDF configuration file may be used. The less efficient, but just as effective, approaches involve using either a FORWARD mapping or directory channel. See Section 3.5.2.