12 May 2003 I have been directed to the habeas.com project, which offers a copyrighted header tag for identifying wanted e-mail. There is a section on the habeas FAQ about whitelisting, from which the following quote is taken: QUOTE Moreover, if too many people add an address to their whitelist (like support@amazon.com), it becomes a tempting target for spammer's to forge as their from address, and their mail gets through. By contrast, if spammers illegally use the Habeas Warrant Mark, we can prosecute them. END QUOTE The crucial thing about RAPNAP validation is, valid messages from support@amazon.com only originate from the e-mail peer machines that such messages validly originate from. The habeas.com FAQ also claims that challenge-reponse systems are really annoying. This is impossible to argue, as it is a matter of taste, but the RAPNAP system, by being centralized, attempts to provide one challenge-response event for the entire system, instead of a separate challenge-response handhsake for every person you correspond with.