[Exim] Exim Config Problems(cc: and aliases)

I have recently installed exim 3.16-1 on my Linux(Redhat 6.1) server, and I
have found an odd problem.
First of all, I'm using exim as a relay, to send messages to my Exchange
Server based on .forward files
in each user's account. Let me lay out my problem.
Someone remotely sends an email to my domain('mydomain.com'). It doesn't
matter who the primary recipient
is, but the message has to be carbon copied(cc:'d) to
'someuser@???'. If 'someuser' actually
has an account on my Linux server, as well as on my Exchange Server,
everything works fine. However,
if 'someuser' is actually an alias(would look like "someuser: anotheruser"
in /etc/aliases), the message
disappears - no bounce-back, no log entries, or anything. If I look in
/var/log/exim/mainlog, it doesn't
mention anything about the message in question.
I'm stumped, so any help with this is greatly appreciated.