SMTP Authentication against database on separate POP/IMAP host

[Paul R. Ganci]

I have been googling for several days now and still have not come up 
with a solution for this problem. I inherited two machines one of which 
runs the POP/IMAP servers and contains a virtual user PAM database. The 
other machine runs an SMTP server which is used for relaying the email 
for the internal subscribers of our small rural wireless ISP. The SMTP 
relay is closed off from the outside world, but I have never liked this 
solution because any of our subscriber machines could be hacked and used 
to turn the SMTP server into a open relay or worse. Additionally many of 
subscribers travel and want access to the SMTP server which I can not 
give them.

I want to setup SSL and authenticate our subscribers using the SMTP 
server against the PAM database kept on the host running the POP/IMAP 
servers. Has anyone done anything like this before? I am open to 
suggestions. I was hoping to avoid duplicating the PAM database on the 
SMTP server if I can. I would appreciate references to any 
documentation, references etc. Thanks.

-- 
Paul (ganci at nurdog.com)