E-mail and antivirus vendor Deerfield.com will introduce an anti-spam product later this month that will make prominent use of an emerging and controversial spam-fighting method known as challenge-response.

The challenge-response method, also used by Mailblocks and SpamArrest, essentially asks those sending an E-mail to a protected address for the first time to answer a question or enter a code that verifies the sender is a human being and not an automated bulk spamming system. But the approach has raised concerns about the impact it could have on legitimate E-mail marketers and consumers who may be chased from using E-mail if they're asked to perform a task after sending a message.

For its MailPermit tool, due out June 22, Deerfield.com has adopted the open-source SpamAssassin technology--which employs a combination of filtering tactics, including heuristic analysis, blacklists, and a spam-tracking database--as the first line of defense. Its proprietary challenge-response technology is applied to messages that clear the SpamAssassin filters.

CEO Mike Deerfield says he agrees with Microsoft's chief spam-fighting executive, Ryan Hamlin, who said recently that challenge-response is too disruptive as a first line of defense. Using it that way could increase E-mail traffic as much as 400% by creating a loop of auto-responses, Deerfield says.

But Deerfield doesn't believe the occasional encounter with challenge-response will cause consumers to abandon E-mail. "People are always afraid of what they don't know," he says. "Once people experience challenge-response, they're going to realize it's not so bad, and that the benefits will outweigh the few seconds it will take them to complete it one time."

MailPermit, which will be distributed via Internet download, will be priced at $99 for a license supporting up to 25 users. An unlimited gateway license will be priced at $2,000.

MailPermit is coming to the market as spam continues to hit new heights. Earlier this week, anti-spam vendor MessageLabs reported that May marked the first month during which spam accounted for more than 50% of all the E-mail scanned by the vendor's anti-spam service. During the month, one out of every 1.8 E-mails scanned, or 55.1%, of 133.9 million E-mails scanned, was spam, marking a 38.6% increase over April.