I can’t access OWA from outside SBS 2003 Site

SBS serves up OWA from inside the building just fine… but OWA is not accessible and we get no error from outside the firewall. I have the ports open, and OWA with SBS 2000 (Exchange 2000) worked just fine. What is the difference between the SBS 2000 and 2003 setup that is making this broken? Any guidance would be greatly appreciated.