On Wed, 14 Aug 2002, Keith Moore wrote:
There must be a secure method that would allow a receiver to verify whether
or not the sender actually exists as a user on the mail server for the
domain the e-mail is coming from.
this is already possible. it is not sufficient.
It's possible but it's useless as one can't depend on it: too many MTA's
are configured to refuse EXPN/VRFY requests if they were implemented in
the first place.
--
Pekka Savola "Tell me of difficulties surmounted,
Netcore Oy not those you stumble over and fall"
Systems. Networks. Security. -- Robert Jordan: A Crown of Swords