/var/qmail/control/smtproutes contains information for routing mail based on domain (we use it to define an alternative route for internal mail, to the rest). Our lines look something like:
<domain name>:<internal ip address>
:<external smtp server address>
the first lines states that mail for <domain name> goes to <ip address>. all other mail goes to <external smtp server address>.
As for receiving mail, I always get confused, the site http://www.lifewithqmail.org/
is a good source of references for the options available. I think that more than one file under /var/qmail/control/ may need modification.