Could not receive mails, but send perfectly

[dvit77]

Some days ago our server "die", with all of our Exchange and Active Directory structure. Then we have decided to switch to a double SERVER (windows server 2003) structure, one the Main Domain controller which is:
- DNS Server (works fine)
- DHCP Server (works fine)
- File Server
- Print Server
- Have two different network adapter one the LAN, and the other one the Internet router, where the router is redirected, we have configured the NAT for this connections and works fine, offering to the users the possibility to connect to internet

The second server depends from the first one and have:
- Exchange 2003 with sp 1 installed.
- Antivirus software (Panda)
- Also have 2 network adapters one points to the LAN, and the other one to the router (as in the main server). No NAT here.

We have the router well configured as well as the MX and other parameters to arrive at it, because it was working since last week in the previous server.

The problem is that we can send mails to everywhere but we do not receive any e-mail. Also the OWA works perfectly internally but do not work from outside (before it works also...)

Could the problem be that we have the "router" configured in both servers and when something arrives do not know where to reach?

How can we solve this problem?

Any help or idea will be highly appreciated!!

Thank you.