Responding to Another E-Mail Challenge

With challenge/response, senders must prove they’re human before their messages get through.

As if email marketers didn’t have enough headaches, during the past few weeks two separate companies introduced spam-blocking email services that use a system known as challenge/response. It’s a system well worth monitoring, as it appears destined to grow in popularity.

Most spam-blocking systems operate under a presumption of innocence — you’re only blocked if your message comes from the wrong IP address or has the wrong characteristics. Challenge/response operates under the presumption of guilt. Your email is blocked unless it meets certain criteria for making it into the inbox.

The first company promoting this approach (which, incidentally, is suing the second for patent infringement) is Mailblocks, a Los Altos, CA-based startup that promises consumers spam-free inboxes. The second is EarthLink, the nation’s second largest ISP.

If nothing else, the challenge/response approach seems to be part of the Zeitgeist. Although it’s nothing new — other anti-spam players, including Spam Arrest, Vanquish, and MailFrontier Matador, have made challenge/response a part of their architectures — the approach is garnering more attention lately as frustration with spam intensifies.

Challenge/response weeds out any email messages not sent by either a known sender or a human being who can respond to a “challenge” sent by the spam-blocking software. People on the user’s personal whitelist (perhaps her address book), automatically get through. Unknown senders’ emails are dropped in a “quarantine” folder. The system automatically generates a “challenge” email for the sender. The nature of the challenge is different with every system. EarthLink’s allows the sender to request the recipient add his address to the whitelist. Challenges sent by Spam Arrest, Mailblocks, Matador, and Vanquish ask senders to verify their humanity (by way of a visual test).

This poses a serious problem for senders of high-volume or automated email. In my own short, two-day test of Mailblocks, messages from Eddie Bauer,,, Levi’s, Procter & Gamble, and (ironically) EarthLink were placed in my quarantine folder. I received automated responses (also quarantined) from a couple of these companies. None has, so far, responded in such a way as to be allowed into the inbox.

E-mail service providers (ESPs), including those represented by the Network Advertising Initiative’s (NAI’s) ESP coalition, are understandably concerned.

“Ticket [or purchase] confirmations don’t come from a customer service rep’s outbox, they are delivered automatically,” said Trevor Hughes, head of the NAI’s ESP coalition. “Those systems don’t have a person behind them that can go through the computational test to respond to them.”

Tactically, ESPs are building workarounds to deal with the problem and simultaneously developing strategies for the future. For now, Bigfoot Interactive’s Ari Osur says the company monitors inbound email in response to a mailing. It’s routed to a human being, who scans messages for challenges and responds to them.

“You can also do keyword handlers on that reply mail [to find challenges],” he said. “And they would just go through and manually do it.”

For many systems, that’s enough. For EarthLink’s, the user still needs to OK the sender’s request to be added to the whitelist.

“There is no way for the marketer to ‘make sure’ their message gets through the system,” said Jerry Grasso, an EarthLink spokesperson. “The user has to allow it to get through.”

Mailblocks, to its credit, allows users to set up unique email addresses called “trackers,” which they can use to conduct commercial relationships. Mail to these addresses isn’t filtered. The process of setting these up is somewhat confusing. It’s unlikely consumers will go back and change their email addresses with every commercial entity with which they have existing relationships.

Sound confusing and time consuming? That’s why it’s such a concern. Challenge/response requires marketers to battle for each individual email box. There’s no central whitelist or go-to person to contact, making the problem especially difficult.

So far, challenge/response is a fairly small problem. Bigfoot’s Osur said a recent mailing for one client resulted in around five challenges per million messages. The ratio of challenges is undoubtedly growing. Mailblocks, launched just two months ago, won’t reveal subscriber numbers, although it said it’s “getting traction.” EarthLink won’t divulge how many people are using its new system, either, but said it expects half of its 5 million subscribers to be using it by year end.

What to do? Enlist a human to respond to challenges. Ask your newsletter subscribers to add your address or domain to their address books or whitelists. Work to foster dialogue between legitimate marketers and ESPs, and the developers of challenge/response systems. Finally, keep an eye on the development of this technique and prepare to meet the challenge.

Don’t miss ClickZ’s Weblog Business Strategies in Boston, June 9-10.

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