An office moved their production server to a new location. After configuring their new router to allow external Remote Desktop connections against TCP/UDP 3389, the connection was refused.
It was discovered that the server's listening port for RDP had been changed. Once the network address translation was configured correctly on the router, the server allowed remote connections.
To check your listening port for Microsoft Remote Desktop on Windows 10 Pro, open Settings > System > Remote Desktop (Enable Remote Desktop) > Advanced Settings.
Alternative ports are used to support multiple Remote Desktop Connections.
Read more on Microsoft Remote Desktop for Windows 10 Pro here: www.salespartner.co.nz/news/how-to-setup-remote-desktop-in-windows-10-pro
To check your public IP address use checkip.dyndns.org/
To test your router configuration and Network Address Translation / port forwarding rules use portchecker.co/canyouseeme