DRAC is a daemon that dynamically updates a relay authorization map for
Sendmail, Postfix and other MTAs that support it.  It provides a way for
legitimate users to relay mail through an SMTP server, while preventing
non-authorized users from using it as a spam relay. Authenticated users
have their IP address added to the map immediately after they have
authenticated via POP, IMAP, or any other daemon which supports the
DRAC API. By default, map entries expire after 30 minutes, but can be
renewed by additional authentication. Periodically checking mail on a
POP server sufficiently does this. DRAC does not require that the
POP/IMAP and SMTP server be on the same physical host.

WWW: http://mail.cc.umanitoba.ca/drac/