With the new Windows Server´s the Telnet Client is no longer automatically installed. Of course you can install it from the features list but today I saw another way to check if a port is reachable on another server.

It’s a PowerShell command:
Test-NetConnection -ComputerName remoteserver -Port nnnn

So for example you want to check of the Domino Port is reachable on another host just replace the “remoteserver” with the DNS name and “nnnn” with 1352.