The network setup is:
Technicolor router (public IP)
Draytek Router (WAN2-DZM)
Windows 2008 R2 (single domain, GC, DNS, DHCP, Exchange 2010)
The draytek was the original router and everything was working fine inside and outside the network.
By mistake the ADSL connection on Draytek was terminated and we have to use the technicolor box instead. The Draytek is connected to Technicolor LAN3 port and setup as DZM.
Since the public IP has changed, I have amended the mx records with the new IP public IP of technicolor.
I've used MX Tools website to test the MX record above and it seems to be fine.
I have also amended the A records to new IP address:
webmail.domain.com public IP
autodiscover.domain.com public IP
From inside and outside the network I can reach the OWA page, but after entering the correct credentials I receive the following error:
HTTP 500 internal server error
Is there a problem with the certificate or am I missing some ports to open/forward between routers?