This is a great tool to test your server and services like Exchange Activesync and also Autodiscover to check out what could be wrong on your server settings and is making your devices connection to the server fail:
“The Exchange Server Remote Connectivity Analyzer is a web site for IT Administrators to validate and diagnose end-to-end Exchange scenarios. The site simulates multiple Exchange client access and inbound service related scenarios from outside the customer’s infrastructure and reports whether the test was successful. If the test fails, we tell the IT Admin exactly where in the process it failed as well as provide troubleshooting tips on resolving the issue.”~
To test your server just visit https://testexchangeconnectivity.com/ and select the service you wish to diagnose.