writes "The AP reports today that the U.S. government has no plans to create a do-not-spam registry in the immediate future. Why not? They argue that the proper technology is not yet in place. 'A national do-not-e-mail registry, without a system in place to authenticate the origin of e-mail messages, would fail to reduce the burden of spam and may even increase the amount of spam received by consumers,' said the commission."
The moral of the story is: never try. See the FTC's press release
or their report (pdf)