[Exim] exim 4.24 not obeying /etc/aliases

I have Exim 4.24 installed on a linux box (built from source). Exim is
configured to hand off mail to a smarthost. That is all working fine.
My problem is that exim isn't obeying my /etc/aliases file. I have a
really simple aliases file:

root: zxcvbnm@???
postmaster: root
bin: root
daemon: root
ftp: root
nobody: root
operator: root
uucp: root
mailer-daemon: root

But when my system sends mail to root, Exim doesn't send it to
zxcvbnm@???, it still tries to send it to root.

Any ideas what might be happening here?

Thanks,
Bryan Walton