Please check if your (Hosted) Microsoft Exchange Service is correctly configured before trying to use the Synchronizer.
For successful operation, the Synchronizer uses the AutoDiscovery functionality. Please use this Microsoft page to verify your setup:
If both Autodiscover tests fail, then please consult your (local) IT party on how to resolve this situation. Show them this test information for clarification, as it will help you in resolving the issue.
Also, all other tests should finish successfully. If other errors during these tests are found, they should be solved first before continuing.