[GTALUG] Postfix question

I am running a mailserver (Postfix, Dovecot, Spamassassin), and I have some virtual alias maps that send some email to gmail addresses. My question is, is there a way to see if postfix is forwarding the email to the alias list *before* it runs the spam checking? Because I think it might be, which means that I am trying to send spam to gmail, which they take a dim view of (refusing all connections an gumming up my queue). If this is happening, can I get postfix to weed out the spam before running the virtual aliases? Thanks!