You are the Office 365 administrator for your company.
Users report that they cannot sign in to Lync from their mobile devices, but they are able to send and receive
Lync messages by using their laptop computers.
You need to troubleshoot the issue.
What should you do? web site. The MCA tool provides administrators and end users with the ability to run connectivity diagnostics for five common connectivity symptoms directly from their local computer. certificate, web service for Mobility is correctly set up.

A.
From the Office 365 message center, confirm Lync settings.

B.
Use the Microsoft Connectivity Analyzer tool to confirm settings.

C.
Confirm Lync user licenses for the affected users.

D.
From the Lync admin center, verify the external access settings.

Explanation:

The Microsoft Connectivity Analyzer (MCA) tool is a companion to the Microsoft Remote Connectivity Analyzer
One of the five symptoms that can be tested using MCA is:
“I can’t log on to Lync on my mobile device or the Lync Windows Store App” – This test checks for the Domain
Name Server (DNS) records for your on-premise domain to ensure they are configured correctly for supporting
Mobile Lync clients. Also it connects to the Autodiscover web service and makes sure that the authentication,