May 26, 2018
Dynamic Relay Authorization Control, a POP-before-SMTP implementation
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.