Three:
[Warning in advance: I don't run a remailer, and never have, so what follows could be labled uninformed speculation].
I would like to suggest that a remailer could eliminate nearly all it's problems by only sending out encrypted mails - that is, if after removing the encryption that was applied using it's own private key, it finds that the result is plaintext, it simply drops the message. <...> The only bad point:
* All recipients need to have key pairs. Thus, a crypto-only remailer can't be a terminal remailer to mailing lists, newsgroups, or individuals without keypairs.
Simple fix is to add a "Decrypt using this key" header (or prepend to the body, which is "wrong" in that a MTA shouldn't screw much with the body). It should stop spammers since their targets usually won't be expecting encrypted messages etc. and would be much less likely to bother decrypting them. It could still be used as a terminal to a mailing list or newsgroup, just with a bit of extra hassle. Additionally, remailers could advertise selective use of this--i.e. they have certain addresses (mail to news gateways, mailing lists that don't mind anonymous traffic etc.) that they don't encrypt to. -- A quote from Petro's Archives: ********************************************** Sometimes it is said that man can not be trusted with the government of himself. Can he, then, be trusted with the government of others? Or have we found angels in the forms of kings to govern him? Let history answer this question. -- Thomas Jefferson, 1st Inaugural