IETF SMTP Working Group Proposal at

SMTP AUTH is certainly part of the solution but I think this is largely
for user->server communication and not as much for server<->server.

If spam is security problem or not maybe a point of view, what spammers
are trying to do certainly often involves security measures.

But in reality I'm just looking for increased security in email
communication alowing for users and servers to decided the kind of trust
relationship they want to have for that particular communication with
choices between several methods and ability to negotiate what would be
used (like during PPP, it is negotiated what type of transmission it
would be, although analogy is really very remote). In my option, currently
use of email is reducing due to amount of unwanted email and due to the
way protocol is setup that may not allow user to fully rely on it and to
be absolutly certain it was not intercepted, it was delivered to correct
recepient, etc. I think we can work to make protocol and the tools needed
for user to be certain email is received, that extra unwanted email is
likely be thrown out (or at least marked as less secure) and this will
lead to wider use of email and to allow for email to replace some of the
things conventional mail is still used for.