Postgrey is a Postfix policy server implementing greylisting developed
by David Schweikert.

Compared to greylist.pl included with Postfix (2.1.1), Postgrey has the
following additional features:
- Safer database handling: Postgrey does use the logging and transaction
  features of BerkeleyDB to maximize reliability.
- Automatical cleaning of the database: Entries that were last seen
  more than a defined amount of time get removed automatically.