OK, we seem to be making progress here. I tried reconfiguring the mail.cf file and now I can receive mail via Squirrelmail,which I couldn't do before.
I tried running service --status-all | grep postfix like you said, and nothing got returned. (Dovecot is working fine).
The changes I made to mail.cf didn't seem to help. Any idea why postfix might not be listening on port 25?