So, to make sure have your issue right (assuming your internal IP range is 192.168.1.0/24 and your external IP is 126.96.36.199):
You have a router with an external IP of 188.8.131.52. You have a server with an IP of 192.168.1.4. You have a client (desktop) with an IP of 192.168.1.10. The router is configured to forward all connections on port 80 to 192.168.1.4. You have a entry in your name server "www.example.com. IN A 184.108.40.206".
This is due to your usage of NAT with port forwarding. The internal clients will not be able to hit the external IP and get the same port forwarding. This is a limitation of almost every router I have seen. Your best bet is to set up split brain DNS, such that www.example.com. is 192.168.1.4 for your local clients but 220.127.116.11 for the rest of the world.