Cloudmark DesktopOne Pro

Critics across the board say they are happy with the Cloudmark DesktopOne Pro spam filter. The community-based filter hits accuracy rates of between 92 percent and 97 percent in various tests, with less than 1 percent of legitimate mail flagged as a false positive. That effectiveness is reduced when scanning large amounts of older emails at once, however -- hence the difference in reported accuracy rates. One expert found that DesktopOne Pro had issues identifying spam written in Russian or related to tax-time phishing schemes.

Unlike most other programs, Cloudmark DesktopOne Pro supports almost every type of email, including IMAP, POP3, webmail and mail on Microsoft Exchange servers. The software runs constantly as a standalone program. An option toolbar and spam folder are added to Microsoft-brand email readers as well as Mozilla Thunderbird; users of other email services can check junk mail and tweak configurations directly in the DesktopOne program. DesktopOne uses about 200 MB of RAM, TheTechHerald.com reports, which shouldn't affect performance on most modern computers.

Experts report that installation is straightforward and should take less than five minutes. Adding contacts to the program's Smartlist is just as simple, especially if you're using an email client that supports the DesktopOne toolbar. The license (which must be renewed yearly) allows you to protect multiple accounts, as well. A free version offers the same spam-fighting capabilities, but only for a single account. Paid subscribers have access to technical support via email, but that's it.

Several publications deliver excellent reviews of Cloudmark DesktopOne Pro, which is a rarity in the spam filter field. PCMag.com and TheTechHerald.com each deliver lengthy, testing-based critiques. PC World delivers a shorter, yet still informative and testing-based examination of its own. TopTenReviews.com also chimes in, and finally, more than 20 users review the product at Download.com