Spam Filtering: Rid email spam with Spamassasin + Greylist!

Problem

Just like you, I really hate sitting down to begin my work day only to find myself wasting the first 10 minutes removing spam. Though Firebird is smart, it still doesn't recognize junk mail as it should. I could build a ton of filters in Firebird but that is also time consuming, spammers are clever and will find a way to by pass filters and junk algorithms. What is a better solution?

Solution

If you control your own web server, you can setup spamassassin with greylist. Most mail servers have the spamassassin service running. Spamassassin does help a great deal, but in my case some 7 spams per hour were being trapped by spamassassin, some 5 more per hour were still passing through to my inbox. Once I turned greylist on, spam in my inbox dropped to 0 per hour!

How Greylist Works

Initially greylist rejects first time email from sender’s mail server. Real mail servers will re-try after a short delay, but those operated by spammers typically will not. Thus legitimate email still gets delivered, but spam does not. Here is a description of why it works from WikiPedia:

"Greylist is effective because many mass email tools used by spammers will not bother to retry a failed delivery, so the spam is never delivered. A spam sender may retry with a different sender, and possibly a different message, because it has a queue of victims rather than the proper queue of messages that regular mail servers maintain.

In addition, if a spammer does retry a delivery after the waiting period has expired, any one of a number of automated spamtraps will have had a good chance of identifying the spam source and listing both the source and the particular message in their databases. Thus, these subsequent attempts are more likely to be detected as spam by other mechanisms than they were before the greylist delay". (Source: http://en.wikipedia.org/wiki/Greylist)

Memory

Greylist will use more resources initially, until greylist builds it’s black list of spammers. Once that is done, spamassassin will need to run less thus using less memory overall. Some say spamassassin is a memory hog, so spamassassin + greylist is a good combo for server admins to consisder too, giving better email service and saving memory for better use.

In my case, I am saving 9% of memory (averaged over 5 minutes) using greylist. Or you can say I have 9% more memory available for other resources. That may not seem like a lot but I am sure most server admins will agree the savings is useful.

Summary

Assuming everyone who sends you an email has good email service, meaning the mail server is setup properly, spamassassin + greylist is a no brainer. It is still a little early to see if I am getting all my emails :).

I suspect in time spammers will get smart and setup their mail servers to respond properly to trick greylist. But until then, I am happy as Lark.