Network Associates bought SpamKiller from NovaSoft only recently, but it's one of the most technically mature client-side antispam products. Unlike the other standalone spam stoppers reviewed here, Junk Spy, MailWasher, Norton Internet Security, and SpamButcher, SpamKiller supports MAPI connections, principally for Exchange Server but also for Hotmail. It can also read the Outlook address book into its own Friends whitelist. Finally, it has one of the richest filter sets we've seen, giving you extensive power to tweak spam identification. Unfortunately, SpamKiller's maturity doesn't equal stellar protection.

SpamKiller runs separately from your mail program. Spam is filtered into SpamKiller, and legitimate e-mails are sent on to your e-mail client. As with MailWasher, this creates a hole that spam can slip through if it arrives in the mailbox between the point when SpamKiller reads it and when the mail client reads it. To avoid conflicts, turn off your mail client's auto-check feature.

SpamKiller is not alone in this deficiency, but it is a clear argument in favor of the products that integrate directly into Outlook or that filter the POP3 stream on the fly—like Norton Internet Security. On the other hand, this very approach is what lets SpamKiller work with any POP3 mail program. In any event, the timing issue should be a significant problem only for very busy mailboxes.

When SpamKiller identifies a message as spam, you can identify the sender as a friend, allowing any subsequent mail; add a filter on the address, the subject, or other elements of the mail header; send a "bounce" error message to the sender's postmaster; or send a complaint. Finally, as with SpamButcher, you can "rescue" messages erroneously identified as spam. Basically, you send a copy of the message to yourself. The drawback: The To: and From: headers change.

SpamKiller initially marked a fair amount of legitimate mail as spam, so we made prodigious use of filters and friend adding, but the final results were only so-so. Its false-positive rate (legitimate mail in the spam box) was about average, at 4.7 percent, but it let through nearly a quarter of the spam we received.

SpamKiller is mature, and McAfee may be able to make improvements, such as allowing it to filter POP3 mail on the fly, since this technology already exists for VirusScan. In the meantime, it does a good but not impressive job in return for a large amount of user attention.