Postgrey is a Postfix policy server that implements greylisting. When a request for mail delivery is received by Postfix via SMTP, the triplet CLIENT_IP / SENDER / RECIPIENT is built. If it is the first time that this triplet is seen, or if the triplet was first seen less than 10 minutes ago, then the mail gets rejected with a temporary error. Hopefully, spammers or viruses will not try again later, even though such behavior is required per RFC.
1.3601 Sep 2015 19:54
Added subnet support for IPv6 and updated the default whitelist.
1.3503 Jul 2014 18:56
Process names on Linux systems longer than 15 characters are now supported. The default whitelist was updated.