Setting Up an Inexpensive but Powerful Spam-Fighting Box
All of the solutions offered so far cost $500 or more, and many offer far less of a feature set than should be available given today's technology. Not every organization has this level of budget available. If yours is one of these, or you're feeling particularly creative or like getting down-and-dirty with this type of technology, an additional route is available to you: set up a UNIX box (pick your flavor: Linux, OS X, FreeBSD, Solaris OS, and so on) to handle your spam and virus issues with the many powerful, free tools available to UNIX users.
Rather than diverging off into the how's and where's here, check out the "alternate ending" for this series that will appear in the Linux section of InformIT. For some reason, all of the best-of-breed spam-fighting software is available for the UNIX crowd. Why, we won't speculate. Ask your Windows software vendors!