COMMENTARY--Once asked to name the most powerful force he had ever seen, Albert Einstein supposedly responded, "compound interest." If Al were around today, I wonder if "spam" might be a better reply.

Thus far, spam seems as unstoppable as compound interest and, if anything, more powerful. I've tried a number of pieces of anti-spamware and, so far, have found an inverse correlation between their convenience and their effectiveness.

The latest example is Mailblocks, a new service founded by Phil Goldman (the guy who founded WebTV). I think Mailblocks is his way of atoning for the hype his old company unleashed, but he's a good guy and I am happy he's rehabilitated himself.

If you want to see Mailblocks in action, you can visit the company's Web site or just send an e-mail to davidcoursey@mailblocks.com.

If you do the latter, you'll see what everyone sees the first time they either send a message to a mailblocks.com address or an account that Mailblocks monitors. (I can, for example, have Mailblocks grab mail addressed to one of my AOL screen names and treat it as Mailblocks.com mail.)

For those of you who'd rather not bother e-mailing me, here's what happens: The first time you send a message to someone using Mailblocks, you get a message in reply, asking you to authorise yourself.

In order to be authorised and have the message delivered, you must follow a link from the Mailblocks response over to a Web site. There, you'll be presented with a graphic image in which a series of numbers appear. You'll be asked to type those numbers into a box on the page. Doing this correctly makes you an authorised sender and your message, as well as any future messages, will go through.

Mailblocks won't even send its autoreply to obviously bogus return addresses. If a spammer does get past that first filter, Goldman figures no spammer is likely to do the number-entering step required to get messages past Mailblocks.

Goldman filed for a patent on this technology in 1997 and recently received it. This makes me wonder where he's been hiding it and whether something this simple--think of it as the Amazon "One-Click" of spam protection--should really be patentable.

Others can answer that last question. In the meantime, I'll take on a couple of others:

Yes, it works
And it's a tad less bothersome than other spam fighters that create similar "whitelists" of approved senders. Mailblocks does not, for example, follow the lead of others who ask you to reply with a reason why you are sending the e-mail, which the recipient must OK before you are allowed to send the message and become an authorised sender.

I asked Phil how it handles mailing lists. His solution, which I consider both ingenious and kludgey, is to enable users to create as many alias addresses as they need. You give these addresses to senders whose stuff you want to see--like the AnchorDesk newsletter--but also want to control.

Mail to these alias addresses avoids the challenge-and-response routine senders to your personal mailbox must go through to become authorised. But if you start getting a bunch of spam at that address, you can kill it without cutting off your personal mail.

Mailblocks can be made to work with Microsoft Outlook as a mail client and with your AOL, Yahoo, Hotmail, and POP3 accounts. Or you can use it with the Web interface Mailblocks provides, which works quite nicely.

However, as the noted sci-fi author Robert Heinlein once noted, "There's no such thing as a free lunch." And Mailblocks is no exception: A one-year subscription is US$9.95. But (doubtless a nod to Ron Popeil) Goldman is offering a special, early-bird discount: three years for $9.95.

If you find Mailblocks attractive enough to commit for three years, take up that last offer. Because if the company lines up enough users, spammers will take notice and eventually find a way to authorise themselves.

Goldman says he has something up his sleeve if that happens. He'd better. The ongoing war against spam is shaping up to be like the war against any terrible disease, one in which each side keeps leapfrogging the other. In the meantime, you could enjoy some temporary relief from the scourge.

What do you think? Are you happy with your current antispam tools? Would you give Mailblocks a try? TalkBack below or e-mail edit@zdnet.com.au.

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