I have been able to connect to the RT-N66U UI after checking the port of access from WAN under the firewall settings which is port 8080 so I put that and the end of my http:/hostname.dyndns-mail.com:8080, if I change the port of access from WAN and put whatever I changed to on the end of my hostname it will only connect to the router UI.
In the router UI under WAN-Port forwarding I have entered two port forwarding to the same LAN IP one being http and the other https, I have tried adding these ports to the end of the hostname and it times out. I am using windows 7 but I want to connect direct to the Nas through the router without windows running a I did pay someone to do this a couple of years ago with a D-Link router which is now with the gods which cost me $$$$
I am not sure if this matters but I have been using 3G on my I phone to test the connection using my hostname to avoid loop back