Message Processing

I have a virtual domain name. I use Procmail on a Linux system to sort, forward
and otherwise filter incoming mail. I've defined certain e-mail aliases;
addresses that aren't defined are returned using ERRORCODE=67.  If someone sends
an e-mail to more than one of the predefined addresses @mydomain.com, only the
first address in the TO: field is forwarded.

How do I make it so each @mydomain.com is handled and subject to the filtering
of subsequent recipies in my .procmailrc
file?