A new Boston-area company has developed an interesting approach to combating spam - making spammers pay to send it.Vanquish's software is still in limited release to several ISPs that are beta-testing the product, but the company plans to ship the first release in March or April.Vanquish's concept is very simple. Instead of using filters to determine what constitutes spam, the Vanquish system requires e-mail senders to include a penalty button in each message they send to a recipient whose e-mail system or e-mail provider is protected by Vanquish.If a message is spam, the recipient clicks on the penalty button and the sender's bond is debited five cents if the recipient clicks the button within three days of sending the e-mail (every Vanquish account includes a sender bond of up to $2.50 to cover the first 50 or so rejected messages, so that senders of legitimate messages will rarely, if ever, have to put their own money into the bond).Senders that do not include a penalty button in their e-mail will receive an automatic message back from a Vanquish-protected recipient asking them to solve a challenge that consists of entering two graphics-based words from a Web site to which the sender is directed. Upon successful completion of the challenge, the original e-mail is delivered and the user is placed on the recipient's whitelist. If the sender does not include a penalty button or respond to the challenge in a timely manner, the e-mail will not be delivered.An interesting twist on Vanquish's bonding of e-mail senders is they will pay ISPs who have to transport spam. Although Vanquish has not yet determined how much ISPs will receive from the bonds forfeited by spammers, recipients' ISPs will receive the largest single share of the proceeds, followed by senders' ISPs who are also Vanquish partners. Vanquish will retain part of the proceeds to cover their costs of managing these funds.Vanquish is priced at $29.95 as a retail product; ISP partners pay 75 cents to $1 or less per month per user account, and ISPs that pay monthly are charged a $2 fee to cover the cost of the software and configuration.The Vanquish approach is intriguing for a couple of reasons. First, since it uses only recipients' judgment to determine what constitutes spam, it does not rely on any sort of filtering technology, so there is little for e-mail administrators to manage and there are no false positives. Second, while Vanquish does not prevent spammers from sending their messages, the messages simply won't be delivered if a sufficient bond is unavailable or if the challenge cannot be met (the latter being a practical impossibility for spammers).Of course, the downside for any program of this type is that it needs a critical mass of users to be truly effective - for example, if only 10% of all e-mail users adopt this system, it will have little impact on spammers. Still, even in the absence of a critical mass of users at this point, Vanquish is definitely worth a look.