Filtering is no more a solution to the spam problem than it is to water pollution. The right thing to do is to restrain the producers of pollution, rather than routinely burden someone downstream with the task of cleaning up an unfairly imposed mess. The cleanup task is necessarily an imperfect and expensive business.

There is no federal law against spamming, but Congress might act this session. A good law would ban bulk unsolicited commercial e-mail and let individuals who are spammed sue the spammer, just as they currently can sue junk faxers. A bad law would let spamming continue provided the spam is labeled with "ADV" or some such indicator of an unsolicited advertisement in the subject line.

The other side by Paul Graham
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Debate the issue with Graham and Catlett.

The idea, appealing on the surface, is to make spam easy to filter. But this ignores several facts: Not all spammers will label, not everyone has filters, and, even if they did, much of the unfair burden on the Internet infrastructure would remain, as ISP servers forward spam to networks only to have it deleted at some later point.

Spam has grown in recent years from less than 10% of all e-mail to about 40%. If it continues at this rate, the resources required simply to delete most of the junk before it is forwarded will run into billions of dollars. This is an unfair tax on consumers and organizations.

Filtering by ISPs and corporate networks is commonplace, but filtering is and will always be an imperfect process. Filters inevitably make two types of errors: false negatives, in which they let a piece of spam go through; and false positives, in which they throw out something that the recipient actually wants. ISPs are forced to be conservative in their filtering to avoid false positives, which can be costly for businesses that rely on e-mail as an interface to customers for sales and service.

Although filtering technology has become extremely sophisticated, spammers play the cat-and-mouse game with great agility and currently hold the advantage of larger numbers and little economic or legal incentive to stop. When appropriate legislation increases those incentives, filtering at the network level still will be necessary, but it should not be a major systemic cost. If the public resigns itself to tolerating spam and accepting the burden of filtering it (imperfectly), users' disenchantment with e-mail likely will reach a tipping point where many abandon e-mail.