Microsoft blames massive Microsoft 365 outage on maintenance bug

A $60B Vote of Confidence

Microsoft's massive Microsoft 365 outage on July 23, 2026, has left many wondering about the reliability of the company's cloud services. The outage, which affected various services including Teams, SharePoint, and OneDrive, was caused by a maintenance bug in Microsoft's automated network maintenance request system. The bug mistakenly removed IP routes from more devices than intended, disrupting network traffic and causing connectivity failures, increased latency, and problems accessing numerous cloud services.

The incident highlights the importance of robust safety checks and automated processes in maintenance requests to prevent similar outages in the future. Microsoft's engineers began investigating the issues immediately after the outage began and later traced the route removals to a datacenter in the West US region and linked them with the recent maintenance activity. Microsoft initiated a rollback of the maintenance change at 1:45 PM ET, which was completed at 2:26 PM ET. The rollback restored the affected network infrastructure and allowed Microsoft 365 services to recover.

The company is now conducting a full internal review focused on the safety checks and automated processes used to execute maintenance requests. Microsoft said it will publish a final Post Incident Review after completing its investigation, which is usually within 14 days. The review will focus on the safety checks, automated maintenance request change process, and more as the company progresses through its post-mitigation internal retrospective.

Why Cursor?

The Microsoft 365 outage has raised questions about the reliability of Microsoft's cloud services. The company's automated network maintenance request system, which is designed to ensure the smooth operation of its cloud services, failed to prevent the outage. The incident highlights the importance of robust safety checks and automated processes in maintenance requests to prevent similar outages in the future.

The Road Ahead

Microsoft's full internal review will focus on the safety checks and automated processes used to execute maintenance requests. The company will publish a final Post Incident Review after completing its investigation, which is usually within 14 days. The review will focus on the safety checks, automated maintenance request change process, and more as the company progresses through its post-mitigation internal retrospective.