[Exim] exim external transport

Sorry for a possible duplicate post.... I'll try to explain it...
Basically, what I want to happen is that Exim is to handle mails sent to
bbs.psinergy.com, which is the FQDN of my Citadel BBS installation(I wonder
if I'm doing this incorrectly, my Citadel BBS software is running on the
same machine psinergybbs.com). Citadel users don't exist as Linux users,
and it uses citmail as mail transport. Now how do I tell Exim that when it
receives mail for someone@??? to let citmail handle it? I
can send email from my Citadel BBS to the outside world, it's the receiving
that's encountering problems. I hope this helps on the way to solving my
problem... Thanks to those who replied to my previous posts..