Comment Articles

Spam killers may lock up your email

Declan McCullagh, CNET News.com CNET News.com

Published: 28 May 2003 10:38 BST

I recently wrote about patents relating to this technology, known as challenge-response technology. Basically, when your mailbox is protected by a challenge-response system, people who try to contact you will be greeted with a response saying something like "click on this link to deliver this message" or "type in the word you see in the box above." The idea is to block increasingly obnoxious spam bots but still let actual humans get in touch with you.

In theory, well-designed challenge-response utilities won't challenge mail from known correspondents or mail that you've actually asked to receive. Unfortunately, many current challenge-response systems are poorly designed, which could wreak havoc on mailing lists and other legitimate communications. This could make email far less useful than it is today.

It's already starting to happen. SpamArrest.com began challenging mailing list messages last year. Recently Mail-block.com and iPermitMail.com followed suit.

When that happens, the operator of the mailing list receives a message -- from each subscriber using the poorly designed challenge-response utility -- that asks the list operator to respond to the challenge. Replying to a handful of challenges is no big deal, but if many subscribers start using poor challenge-response software, it will pose a serious problem for mailing list operators.

Big corporations may be able to afford to hire someone to sit in front of a computer and spend all day proving they're not a spam bot, but nonprofit groups, individuals and smaller companies probably can't.

Challenge-response systems, ironically, share some characteristics with spam: In small quantities, both are only mildly annoying to the recipient. But as quantities increase, they make it more difficult to use email at all.

MailFrontier.net is a good example: it prevents its users from signing up to mailing lists unless the list operator manually intervenes to answer the challenge, a process that is exactly backward.

The enormous growth in spam means that challenge-response technology will become more popular. EarthLink recently announced it would make a challenge-response system available to its customers by the end of May, and the field is wide open, with no market leader so far.