Jonathan Rauch has a typically good column on spam and ways to deal with it. He recommends what I think is the best approach: that we have property rights in our email inbox!
The spam problem, though new in form, is an instance of a very old and familiar dilemma, which economists often call the tragedy of the commons. When any resource is both valuable and freely available, people tend to overuse it. Moreover, everyone anticipates that everyone else will overuse it, so everyone tries all the harder to get while the getting is good. The result is a run on the resource. The tragedy is that everyone’s least-favored outcome — the depletion or exhaustion of the resource — is assured.
Centuries of theory and practice have unearthed two effective remedies. One is to appoint a conservator with the unique power to mete out the resource: say, the U.S. Fish and Wildlife Service. The other is to create property rights to the resource and allow a market to develop. What people own, they conserve.
In the case of e-mail, the valuable resource at issue is my attention, and the problem is that access to it is essentially free. People who really want to talk to me need make no more effort than do people who merely want to waste my time. In fact, spammers expend less effort than real people do, because a computer does all their mailing for them, whereas you would need to sit down and write a message.
Rauch then explains why spam bans and ISP exhortations will not work as well as our having property rights in our own inboxes.