Firewall blocking WAF-Port - why?

Hi out there!
Now my Active-Sync and OWA are working properly.
But only, if I use DNAT (12433 to 433).
If I try to use WAF (after disable the mentioned NAT-Rule), the firewall is blocking the traffic from the smartphones to Port 12433 on my ASG-WAN-
interface.
A new firewallrule doesn't stop this behavior.
Do I have forgotten something to configure? Any hints?

Thanks for your help!! J.Kontny