Add-On Spam-Fighting Tools for Microsoft Exchange Server
Many add-on tool options are available; we'll take a look at six different possibilities. The first of these is available from Microsoft (or will be soon), and is called the Intelligent Message Filter. While this product is still in beta, so far the descriptions suggest that it offers a Bayesian filter and feature recognizer with an internal scoring approach to what its engine finds. Administrators can set two score thresholdsone at the mail gateway, and a lower one at the mail store itself. Mail scored higher than the gateway threshold gets quarantined (for administrators to deal with) or discarded altogether, while mail with lower scores gets passed on to the mail store. At the mail store, the second threshold is used to determine whether the mail ends up in the recipient's inbox or junk mail folder.
The remaining add-on tools are available through third parties. One place to track not only what tools are on the market, but also what features each has and see reviews on how well each works is Spamotomy. Select the Tools tab, choose Server Software, and if you have a specific Windows version in mind you can select the version, too. In our case, we'll focus on Windows in general. Another excellent site to watch is Spam Links.
One favorite of Windows spam fighters is GFI MailEssentials, which offers Bayesian filtering along with some feature-recognition capability; the ability to block mail based on DNSBL listings; and basic quarantining of mail flagged as "spam," either system-wide or on a per-user basis. MailEssentials offers a broad range of tests, but the results are viewed individually, not as a wholemail that triggers any one of the tests will be flagged as spam.
This product can also be integrated with GFI MailSecurity to add virus filtering on your mail server. MailSecurity also supports quarantining of mail with dangerous file attachments. Quarantine management facilities are provided, but only for the administrator, who can then decide which blocked mail items should be delivered to end users.
Another popular solution is Clearswift's MIMEsweeper family of products, including the MAILsweeper Business Suite. This package takes care of just about everything except viruses, though it integrates with third-party antivirus software. Bayesian filtering, DNSBL lookups, feature recognizers, and dangerous-attachment checks are all standard, although, as with the GFI products, the tests are performed individually rather than comprehensivelymeaning that if a single test comes back as positive, the mail is flagged as spam. The quarantine management facilities are quite rich, but they're still limited to administrators and certain designated classes of users. There is still only one quarantine. Administrators can view the contents of the mail within the quarantine, while the assigned privileged users can view just the subjects in case an administrator isn't available to release items from the quarantine.
Yet another favorite among some is NetIQ's MailMarshal, which offers feature recognition; dangerous-attachment detection (for viruses, worms, and so on); and DNSBL lookups. Quarantine management features also allow end users to rescue their own blocked mail. Once again, though, any one of these tests will flag mail as spam.
There's also the Brightmail family of products. Brightmail's Anti-Spam Enterprise Edition offers broad-spectrum coverage, including feature recognizers, DNSBL lookups, whitelists and blacklistseven a full-featured quarantine manager for administrators and end users. The only conspicuously absent features, in fact, are Bayesian filtering and checks for dangerous attachment types. It does, however, work with BrightMail Anti-Virus, which was developed with the help of Symantec, of Norton Antivirus fame.
Finally, there's McAfee's SpamKiller for Microsoft Exchange, which is built on top of the UNIX, Linux, and OS X favorite, SpamAssassin. While a desktop version of this product is available for Windows, we're concerned with the server version here. Like its free UNIX cousin, McAfee SpamKiller for Microsoft Exchange provides feature recognizers, DNSBL lookups, Bayesian filtering, whitelists and blacklistsall in a comprehensive scoring framework that lets you get an overall picture of how "spammy" the mail is before acting on it. System and user quarantines are supported in the form of a system junk mail folder and a junk mail folder for each user. Virus scanning must be handled separately, however, and there's no testing for dangerous attachment types.
Many more tools are available in this category. It's worthwhile to do some more research if this is the avenue you decide to follow.