OWA/Exchange 2003

I just installed email security appliance (email/spam filter) recently, and
when I do OWA I get logon prompt for the email security box but not for
outlook web access. The email security box forwards everything to the
exchange server through port 25. Both the email security box and the only
exchange server 2003 is behind the firewall. I get email back and forth with
out any problem, the problem is with OWA. what do I need to do? open a port
or forward a port? I am confused, please help.