One of the most galling things about spam is that it costs money. If you don't filter it, spam consumes bandwidth, storage, and time--but to prevent that, you might have to pay for filtering software or services. This adds insult to injury: If spammers didn't spam you, you wouldn't have to pay to keep from being spammed! Fortunately, free and low-cost filtering solutions do exist.
In the UNIX world, SpamAssassin (see the first URL below), which runs on Linux, has long been the king of free spam filters and has been widely adopted as a no-purchase-cost solution. However, SpamAssassin requires a certain amount of Linux expertise to set up and run. You can find free and commercial tools that incorporate SpamAssassin filtering for Windows clients and Exchange Server systems; I haven't tested any of those tools yet, but when I do, I’ll tell you about them in this column.
Microsoft Exchange Intelligent Message Filter (IMF--see the second URL below), combined with Microsoft Office Outlook 2003's built-in Junk E-Mail Filter, is providing yeoman service at many sites. I use it at home and at work and have been pleased with its filtering efficiency, especially given its cost (free, assuming you already have Outlook 2003). However, IMF requires Exchange Server 2003, so sites that haven't upgraded yet can't take advantage of it without installing an Exchange 2003 SMTP bridgehead.
The RegEx Filter (the more familiar name for Doug Swallow’s Mail Server Content Filter, which I’ve written about before--see the third and fourth URLs below) remains a worthy spam filter--if you can figure out how to install and manage it. The RegEx Filter doesn't seem to have been updated in a while, though, and it requires you to manually tweak the filters, a task that’s somewhat akin to cleaning out your own sewer pipes.
At the moment, my favorite free filtering solution is the “lite” version of the brand-new Singlefin Enterprise Email Filter (see fifth URL below), which offers a subset of the company’s regular product. Singlefin’s products provide a well-regarded hosted filtering service; the lite version is free and the regular version is free for your first 10 mailboxes. Of course, this is a savvy marketing move on Singlefin's part. There are so many antispam products and services on the market that it's difficult for one vendor to stand out. An offer like this is an effective way to get some attention and add new customers.
Singlefin’s offering is an attractive proposition for a number of reasons. First, the product works with any version of Exchange; you simply point your DNS MX record at Singlefin's server for filtering. Second, because this is a hosted solution, there's very little administrative overhead. Third, because the filtering happens at Singlefin's site, your bandwidth isn't wasted by taking aboard spam that you later have to dump. Of course, if you have more than 10 mailboxes, you'll want to explore other free solutions or switch over to a commercial product. If you do qualify for Singlefin's offer and decide to try it, I'd love to hear from you after you've used the service for a bit.
SingleFin Enterprise Email Filter