Smaller ISPs say Comcast and AT&T maintain huge databases of email servers that send out spam, so they can stop spam messages from reaching their users' mailboxes. Problem is, their system for adding a server to the "blacklist" is a mystery and often marks non-offending servers as spammers.

Once an ISP's email servers get added to a blacklist, none of its customers can send email to any of Comcast's 9 million or AT&T's 7.4 million subscribers.

Jon Newell, president and CEO of local internet provider IPNS, says one of his 22 employees must watch the blacklists every day, at a cost of thousands of dollars annually. He says it often can take months to get off the list. All the while, Newell's non-spamming customers complain that they can't send emails to their clients.

And Ken Perkin, tech support manager at another local ISP, Sterling Communications, says his company had recently gotten off the AT&T blacklist, only to learn it got added again to that list last week.

Perkin and Newell both agree that spam is a problem (who doesn't?), but they say big ISPs' response is overboard because their smaller, managed networks can prevent huge spam bombardments from originating on their servers.

AT&T didn't return WW's calls, but Comcast spokeswoman Theressa Davis says Comcast has reduced spam by 70 percent since ratcheting up its spam-blocking last year.

"This isn't really for competitive reasons," Davis says."This is about fighting spam for everyone on the Internet."

But Newell says the effect is to encroach unfairly on his business.

"If you're Comcast and you want some of my 4,000 domains," Newell says, "this is a good way to get 'em."