There aren’t a lot of free alternatives for doing anti-spam on an Exchange box. If you’re using Exchange Server 2003, you must of course immediately install SP2 (if you haven’t already) and make use of the Intelligent Mail Filter. If you’re still using Exchange 2000, though, what do you do? GFI used to offer a free version of their MailEssentials program, but that’s been discontinued.
This question just came up on a mailing list I read, and it tickled the back of my head. I thought I remembered seeing news of a SpamAssassin plug-in for Exchange, so I went digging — and behold the following from Christopher G. Lewis:
So now, using the CDO Message’s GetStream method, I could write the message object to a text file, and then using the ADO.Stream’s LoadFromFile method I could reload the processed file! Instant SpamAssassin headers.
I’ve not used it — so I can’t comment on its robustness. It looks like SpamAssasssin on Windows doesn’t scale well, so I wouldn’t recommend using it on a heavily loaded server, but it’s another option for smaller sites that don’t have the money to spend on commercial software and don’t want to deploy a UNIX box to run as their mail gateway (although if you go that route, I highly recommend Wietse Venema’s excellent Postfix MTA.