Troubleshooting Outlook connectivity issues with Office 365 is tricky. Administrators can use two valuable tools provided by Microsoft to identify and even fix client related connectivity issues.
Start with the Outlook account problems test page in the Office 365 portal. You need to log on as the Office 365 user having issues.
The site tests for the following:
If no issues are identified after you've logged on to Office 365, move to the next step.
The Microsoft Support and Recovery Assistant (SARA) for Office 365 is click to run tool that is installed and executed locally.
These two tools fix most of the Outlook connectivity issues you are facing as an Office 365 administrator.
Enjoy Office 365