tcp 0 0 *:81 *:* LISTEN 4802/ispconfig_http
The ISPC server is listening oke.
When I attempted to login to https:www.mydomain.com:81 (after repointing the router) there was no website IE could find.
Are you sure your router forwards port 81 to you server (behind the NAT)? It should be
but I assume this is a typo in the posting on the forum.
What should work is
There's no need to obfuscate 192.168 addresses, as these addresses are not reachable from the Internet anyway. The image you attached when you go directly to the machine IP is the regular webserver for your websites and is complete independent from the ISPConfig webserver.