Applies to: Office Communications Server, Communicator

Similar to the Exchange Connectivity Test Tool (https://testexchangeconnectivity.com/), Microsoft has an online tool to test external connectivity for Communicator and OCS.

Here it is: https://www.testocsconnectivity.com/

Please note, the site is still in beta. It’s recommended not to use your normal account, but create a test account that you’ll delete when you’re done with testing on that site.