Poor Man’s Greylisting

No, but it exploits the same noncompliant behaviour of spamware and viruses, including those that spread via internal SMTP engines. Greylisting is an approach promoted and rigorously tested by Evan Harris. It is sensible, RFC-compliant, time-proven, and valuable as one part of a multilayer defense against spam.

If you run a mail server and are serious about cutting down the spam intake, then you will want to read up this article. It’s rather lengthy, but if you don’t mind getting into a tweaking mood, you may have a happier inbox.

Source: Jorey Bump