SSL SMTP Relay in DMZ

[Curtis Vaughan <curtis@npc-usa.com>]

I don't know how to correctly title this letter, but hopefully people 
have an idea of what I'm trying to do.  I'm posting this to the Debian 
list, as it has to do with computing in general more than just mail 
servers.

What I want to know is if the following is possible, and, if so, what 
possible options there are.

I would like to set up a mail server in a DMZ that would accept mail 
only from those clients who have authenticated using SSL.  Given that 
they have successfully passed that criteria, then this DMZ mail server 
would pass the mail off to an internal mail server for further 
delivery.

Thanks for any input!

Curtis