PMDF provides a facility to support mailbox names associated with the local system that do not necessarily correspond to actual users. Such "aliases" are useful for constructing mailing lists, forwarding mail, and synonyms for usernames. A second set of related facilities provide support for "centralized naming" whereby you establish, for instance, mail addresses of the form first.last@example.com for all of your users. There are several advantages to such centralized naming systems: the addresses are simple, they provide added security in that they make no reference to internal account or system names, and, because they lack reference to account and system names, are more stable.

The concept of aliases, mailing lists, and mail forwarding are very closely related in PMDF as they are all effected through the use of PMDF's alias facilities, described below. Perhaps less obvious, is the relationship between mail forwarding and centralized naming schemes. To support centralized naming, a mailer must not only be able to convert internal addresses such as jd001@vax1.example.com into John.Doe@example.com in all outbound mail, but also be able to recognize incoming mail for John.Doe@example.com and forward it to jd001@vax1.example.com. Hence the relationship between centralized naming and mail forwarding and, in turn, aliases.

Finally, as will be pointed out in Sections 3.5 and 3.6, there are several different ways to effect forwarding and centralized naming. The different approaches vary in efficiency and which approach you can use will be largely dictated by the regularity of the mapping between internal and centralized addresses: the more susceptible to pattern matching a mapping is, the more efficiently it may be implemented.