A new e-mail-forwarding service called boxbe.com tackles spam using an economic approach: users charge a fee for access to their inboxes.

Boxbe, in turn, provides users' anonymous demographic information to advertisers, says Thede Loder, the San Francisco-based company's co-founder. The goal, says Loder, is to give boxbe users control over messages they receive, ultimately giving them access to ads that are more in line with their tastes, and, in the process, letting them collect a couple of extra bucks each month.

The idea of managing e-mail by leveraging economics has been tested before. Recently, AOL announced an initiative to charge senders of bulk e-mail a fee to ensure that senders are legitimate. The system, which uses Goodmail, authenticates e-mail, ensuring that certified bulk mailings make it into AOL users' inboxes.

Boxbe differs in that it lets individuals decide how much to charge advertisers and the payment goes directly to the individual. "The main advantage of this approach is that it tries to take into account that different people value commercial e-mail differently," says Jeffrey MacKie-Mason, professor of information, computer science, economics, and public policy at the University of Michigan.

MacKie-Mason has been familiar with Loder's work on the economics of spam since Loder was a graduate student at Michigan. "Some people don't mind [e-mail advertisements], and some people do," he says. "With boxbe, you can set your own price for how easy you are to reach."

To use the service, you need to sign up for a boxbe e-mail address. In the process, you fill out forms about your interests, income, and geographic location. The more information you supply, says Loder, the more your inbox is worth to an advertiser.

Boxbe doesn't replace your existing e-mail; instead, it acts as a public e-mail address that you can put on your blog or MySpace profile. Your boxbe e-mails are then forwarded to your more private account at, say, Yahoo or Gmail. "We certainly don't expect people to use boxbe as a principal e-mail address," says Loder. Your friends already have your private e-mail address, he says, so they won't have to go through boxbe. He adds that the service is more for people who are looking to take advantage of e-mail offers, and those with public e-mail addresses who want a way to screen incoming mail.

When an advertiser or someone who isn't approved by you sends an e-mail to your boxbe address, it immediately bounces back, requiring the sender to either take a test--to verify that he or she is not automated spamming software--or pay the fee. "If it's an advertiser's first experience with us," says Loder, "their messages won't go through [to the user's inbox] unless they are preapproved." He says that boxbe will be releasing an open-source software tool kit in the coming months that lets advertisers incorporate boxbe's tactics into their e-mail campaigns. The software will let the advertisers automatically post a payment or skip e-mailing a boxbe user whose price is too high.