Microsoft Outlook outage cause seemingly revealed
Microsoft is investigating failed server checks as a possible cause of the Nov. 12 Outlook outage and is testing a fix on some affected servers.
On Thursday, Microsoft experienced an outage affecting its Outlook service, as well as other Microsoft 365 services such as Teams, Exchange Online, and Copilot. The company has revealed that a specific component responsible for checking server health may have been the cause of the failures. This component, which runs automated health checks, was found to be malfunctioning on some affected servers.
Microsoft's service health update stated that these failed health checks led to servers going offline in multiple regions, contributing to connection issues. In response, Microsoft is deploying a targeted change to bypass the problematic component on a subset of servers, hoping to restore their functionality. The company is also taking steps to prevent more servers from going offline.
As of now, Microsoft has not identified a recent change that coincided with the start of the outage. The issue initially impacted Exchange Online mailboxes in the Americas, with parts of the infrastructure under heavier load during the event. Users reported trouble accessing their inboxes and sending or receiving emails, with over 130,000 problem reports logged on Downdetector by around 1 p.m. ET.
Microsoft's automated recovery systems have since been working to reduce the disruption. For the latest updates, users can check the Microsoft 365 admin center or the public service status page.
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