[Exim] Mail redirection

Hey, before you flame me, I've looked all over,
and can't seem to find out how to do this anywhere.
I read all the FAQ too.

Basically, i want to set exim up so that when a user connects
to my server and sends an e-mail that has recipient name
without a domain (i.e. anyname) exim will add a specified
domain to the recipient address before it sends the mail out..
(i.e. anyname@???)

I can't seem to find this anywhere....
I would really appreciate it, if someone could help me out.

~Aaron Vose