The User Database is a special database file that you create for use
by sendmail. It causes sender and recipient
addresses to be rewritten under control of an external database.
Ordinarily, any local address is first looked up in the
aliases database. If it is not found there, that
user’s ~/.forward is next
examined. If the User Database is enabled, the address is looked up
in that database after aliasing and before forwarding, but only if
the selected delivery agent has the
F=@ flag set
In the sections that follow, we describe the use of this database in detail, but first we will note a few important points.
Although we illustrate here that a lookup can be done using a database file, a remote lookup can also be done via a User Database server, or via a network service. Those forms of lookup are described in UserDatabaseSpec.
You can also look up addresses in the User Database with rule sets
userdb database-map type. To do so, you
declare it like this:
Kname userdbswitches field