How to: Postfix as mail relay with greylisting support using SQLgrey
Greylisting is a very efficient technique for fighting spam and can reduce the spam messages in your mailbox by more than 90%. It uses the fact that most spammers only try delivering their spam-mails once, whereas real mail transfer agents (such as the ones regular e-mail service providers are using) try delivering each message up to 4-5 days before they give up.
I have always wondered why most ESPs don’t offer greylisting for their mailboxes, but only rely on less effective and resource-hungry post-retrieval filter methods. Unfortunately, my e-mail provider is one of them so that I get at least a couple of spam mails a day …
Luckily, it is very easy to set up your own mail relay with greylisting support, i.e. a mail server that simply forwards the mail to your real provider once it passes the greylist-filter.
This little tutorial describes how to set up Postfix and SQLgrey as mail relay.