First of all, we do not block spam messages once they've been accepted by our mail server and addressed to a valid mail address. The reason? No spam filter is 100% accurate. If you want to throw them away, then go ahead. We just won't make that decision for you. So how do we fight spam?
- Greylisting. If you're not familiar with this, I suggest reading up on the subject if you have any interest in the subject of spam reduction. Simply put, it means an unknown sender has to attempt delivery of the same message TWICE within a certain interval. Mail servers that adhere to the SMTP standard will do this automatically, while most spam and virus zombes usually don't.
- SpamAssassin. After accepting a message into the mail queue, we let our spam filter loose on it. SpamAssassin is perhaps the most well known and precise spam filter available. Using thousands of rules and algoritms it assigns a score to each message. This score is finally used to classify the message as SPAM or not.