Proxy 2 & Exchange 5.5 behind router

[Gersen]

I'm battling a configuration change in a client's network and I seem to be stumped. They switched from an ISDN line to a DSL line. Formerly, they were connecting with an NT 4 Server running MS Proxy Server 2, and the external interface of the Proxy was on a public IP address, and the internal was on a private address.

Now that there's a Cisco router in the loop, and they haven't purchased any static IPs (their provider keeps their name pointed to their dynamic IP address with dynamic DNS, I presume), the only public address is the outside of the Cisco. Between the Cisco and the Proxy, I have a non-public subnet, then a different non-public subnet for the rest of the network.

DSL ==> CISCO RTR ==========> PROXY SVR============>network
/ / / /
DHCP 192.168.1.1 192.168.1.2 10.0.0.2

Exchange Server 5.5 runs on the same machine as Proxy 2.0.
I can no longer get incoming mail through the Internet Mail Connector. I can send it outbound, no problem.

Yes, the DNS has been update to point to their new public address.

What am I missing to make Exchange receive incoming messages?

Thanks,

Gersen