ENDIAN Firewall - access between servers on orange network

I am new to EFW and have successfully installed my red, green and oragnge networks. I have serevral servers on the orange network which I can access from the green and externally without any problems.

On the orange network I have server1 which is a web server and server2 which is a mail server. Each have their own external IPs. When I try to browse to server1 (server1.domain.ltd) from server2 the system resolves to the external address but fails to reach server1.

If I add server1's internal address to my hosts table on server2 (192.168.1.5 server1.domain.ltd) then I have no problem accessing the pages on server1.

How can I setup EFW to make server2 see server1 using server1's external address?