Ok, not 100% sure what i've done wrong here but on my previous vigor router, I could access outlook web access, i've now changed routers and when I type my https://mydomain/exchange/ it displays the routers login box, what have I not setup?

Have you forwarded port 443?

It's probably conflicting with the SSL VPN port, depending on what firmware you've got on the router, you can fix that by either changing the HTTPS management port under System Mainenance and Management OR under SSL VPN and General Setup, which also defaults to 443.

You were correct it was conflicting with the SSL VPN, thanks.