Microsoft 365 stopped working.

Check Microsoft 365 admin center → Health → Service health first, because simultaneous connection failures across all Microsoft 365 services may be an active tenant-impacting incident rather than a problem with your internet connection.^1^

Check for an active incident

1. Sign in to the Microsoft 365 admin center with an administrator account.
2. Open Health → Service health.
3. Under Active issues Microsoft is working on, look for incidents affecting Exchange Online, Teams, SharePoint Online, OneDrive, or Microsoft 365 generally.
4. Open any matching incident and review:
   • User impact
   • Affected services
   • Status
   • Latest update
   • Any published workaround

Service Support and Helpdesk administrators can also view this page. If an incident is listed, no local repair should be performed unless its instructions require one; monitor the incident there until Microsoft reports Service restored.^1^

If the admin center itself cannot be reached, use the public Microsoft service-status page. It is a backup view and is less tenant-specific than the admin-center dashboard.^2^

If no incident appears

Determine whether this is tenant-wide or limited to the device:

1. Ask another user to open Outlook or another Microsoft 365 service.
2. Try the corresponding web apps in a browser. This is not another general internet test—it distinguishes a desktop-client problem from a Microsoft 365 account or service problem.
3. If the web apps work but installed applications do not, run the appropriate Windows diagnostic:
   • Open Get Help.
   • Search for Microsoft 365 network connectivity test.
   • Complete the prompts and review its findings.
   • If applications cannot sign in, also search for sign in to Microsoft Office and run that troubleshooter.

These troubleshooters require Windows 10 or later and must run on the affected PC.^3^

If the diagnostic reports blocked Microsoft endpoints, give its results to the network administrator. Microsoft documents that HTTPS failures, proxy filtering, or TLS inspection of critical Microsoft 365 domains can prevent some or all services from connecting even though ordinary websites remain accessible.^4^

Report or escalate the issue

If multiple users are affected but nothing appears in Service health:

1. In Health → Service health, select Report an issue.
2. Include the exact text “Connectivity to your server”, the approximate start time, affected services, number of affected users, and whether browser access works.
3. If diagnostics pass but the failure continues, open a Microsoft support request from the admin center and attach the diagnostic results. Microsoft recommends checking service health before connectivity testing and escalating when tests pass but the issue persists.^5^

Avoid reinstalling Microsoft 365 or changing Outlook server settings at this stage: those actions target individual-client or email-only failures, while the reported symptom affects all Microsoft 365 services.

References

1. How to check Microsoft 365 service health
2. Microsoft 365, Dynamics 365 & Power Platform incident readiness for Microsoft Engage Center
3. Microsoft 365 troubleshooters | Microsoft Support
4. Microsoft 365 Network Insights
5. Microsoft Remote Connectivity Analyzer