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Currently, I rely on Gmail to weed out SPAM because the anti-spam software on my hoster's mail server is so crappy, and besides, it doesn't provide a good web UI so users can tag false negatives and improve its recognition rate.

But I don't like to depend on Gmail, especially for sensitive corporate e-mails, and I was wondering if there were open-source anti-spam solutions that were as good, or close to Gmail's?

Thank you.

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up vote 1 down vote accepted

I have some pretty good results with Postfix built-in checks, various blacklists and SpamAssassin. You won't have any Web UI with these solutions, but instead, you can train SpamAssassin by moving spams in a specific IMAP folder.

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I was going to recommend SpamAssassin too - which does other checks in addition to bayesian filtering. Including RBL (and SPF. from/reply-to mismatches and more) – symcbean Dec 8 '10 at 10:44
Thanks for the tip. I'll set up a Postfix server + SpamAssasin and see how it goes. – user15318 Jan 6 '11 at 9:13

We cut down 99.5% of spam at my job when we started using Postfix with some basic protocol checks (require HELO, sender in DNS, etc) and more importantly :

  • Dynamic blacklisting (RBL/RHSBL) of the client IP by using (along with a local DNS cache)
  • Greylisting (using postgrey). It maintains an automatic list of "genuine" remote mail servers to accept mail from, by sending "temporary failure" error code to any new mail server it sees (one that has never sent mail to anyone at your house). More than 99% spam servers will never retry to send mail, while genuine MTAs will retry after some 20 minutes, only incurring a small delay the first time you "talk" to them.
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Edit: I glossed over the open-source requirement, disregard my answer.

It's against my personal principles, but I have really great experiences with the Ironport anti spam appliances (now owned by cisco).

Barracuda not so much, it ate at least an hour's worth of email (unrecoverable).

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