When users outside the WAN type in dns adress and attempt to log in to the OWA server, the server does nothing and displays the login page again. If a user uses the public IP address, they can then log in.
Users within the WAN can specify the server name and login, they don't need to use an IP address.
The OWA accessed by the DNS name works in both Chrome and Safari. It seems not to work in Internet Explorer.