Yes, you are not the only one to have this problem. When you have Cisco router as your basic edge firewall, and perform the NAT on that router, you’ll face a strange set of errors if you try to connect any client (except normal browser) to the Exchange server.

No matter what you do, no matter what you change, no matter which IOS of Cisco, and Exchange version/SP you are using, the RPCoHTTPs and ActiveSync client won’t connect or work.

No, I have no solution for you except having VMware ESXi host with two NIC’s, have one more AD DC, and ForeFront TMG (or any other software firewall you’d like to use) and set the public IP’s on that VM and enjoy the smooth running Exchange server.