Microsoft 365 Outage Hits Exchange Online and Other Services Worldwide
by Bill Giannopoulos · Greek City TimesMicrosoft is investigating a major service disruption that began on Thursday, November 12, 2026, leaving users unable to access Exchange Online mailboxes through Outlook and other connection methods.
The issue, tracked as EX1550543, started in the Americas before Microsoft confirmed it could affect users in any region. A related incident, MO1550821, covers broader connectivity problems potentially impacting Microsoft Teams, SharePoint Online, Copilot, and Microsoft Defender XDR.
Microsoft attributed the outage to a portion of infrastructure experiencing elevated load after a number of servers became unexpectedly unavailable. Failed automated health checks—linked to a specific component that processes server health—caused the servers to drop offline, straining the remaining infrastructure. The company has not identified any recent change correlated with the start of the impact.
In response, Microsoft paused deployments, redistributed traffic across its worldwide infrastructure, began restarting affected servers, and is testing a configuration change while taking steps to prevent additional servers from being removed from service.
Administrators can track updates in the Microsoft 365 admin center under EX1550543 and MO1550821, or at status.cloud.microsoft if the admin center is unavailable.
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