falko Timme, of HowToForge, writes about a way to catch spam e-mail before it even gets into your mail system. Compared with other spam-busting tools such as spamd, this tutorial uses your mail transport agent (MTA), the application that talks to other mail servers to transport e-mail, such as Postfix.
While this does not guarantee for a spam-free e-mailbox, every little thing helps in our war against those pesky spam e-mail.