Gld is a standalone greylisting server for Postfix.

Greylisting is a new weapon to use against spam. For more information on
this technique, see http://www.greylisting.org.

This implementation listens on a TCP port and uses MySQL for storing data.
The server supports whitelists based on sender, sender domain and client IP.
It also supports light greylisting.

WWW: http://www.gasmi.net/gld.html