Any suggestions on spam-caused backup?

We’re running a single Exchange Server on a Windows Server 2003 machine. We’ve also got GFI MailEssentials. Overall, we’re pretty happy with the product — we get a ton of spam, and GFI blocks or reroutes most of it. Sometimes we’re pretty heavily hit, though, and it causes the Exchange queue to back up — sometimes messages only get through an hour or so after they’ve hit the server. Short of going in and manually deleting spam, or turning off the GFI services (which clears the backup, but sends all that spam directly to inboxes), does anyone have any suggestions?

Thanks!