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Microsoft gives initial explanation for outage; says ‘servers were unexpectedly unavailable’
Microsoft says unexpected server failures caused widespread disruption across its services.
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Microsoft has shared an initial explanation for the widespread outage that disrupted Outlook, Microsoft 365, Teams, Copilot and several other services across multiple regions on Thursday, November 12.
The company said the problem was not caused by a sudden increase in user traffic. Instead, several servers had unexpectedly become unavailable, putting extra pressure on the remaining infrastructure and leading to connection problems.
The outage affected users in several countries, with reports spreading to 74 countries and territories within about an hour, according to Downdetector.
Outlook saw the biggest spike, with nearly 130,000 reports at its peak in the US. Microsoft 365 recorded more than 47,000 reports, while Teams and Copilot also faced disruptions. OneDrive and SharePoint were among the other affected services.
Microsoft explains what caused the outage
Microsoft initially said it was investigating reports of users having trouble accessing Exchange Online mailboxes through different connection methods in the Americas. It later confirmed that the problem could affect Microsoft 365 users in any region.
Also Read: Microsoft outage: Users report issues with Outlook, Microsoft 365, Store and other apps
In an update on its official Microsoft 365 Status account on X, the company said:
"While we're working to mitigate impact, we've confirmed the issue may affect Microsoft 365 service connectivity for users in any region, more information will be provided in the Microsoft 365 admin center under EX1550543."
Microsoft later explained that several servers had unexpectedly become unavailable, putting additional pressure on the rest of its infrastructure. It said:
"We determined the elevated load isn't driven by an increase in traffic, but by a number of servers being unexpectedly unavailable, straining the remaining infrastructure. We're working to safely return them to service. More info under EX1550543 and MO1550821 in the Microsoft 365 admin center, as well as status.cloud.microsoft if the admin center is not available to you."
Microsoft shifts traffic and restarts servers
To reduce the impact, Microsoft began redirecting connection traffic across its worldwide infrastructure. It also paused deployments and started restarting affected servers.
The company said:
"We're aggressively pursuing all pathways to reduce impact. We've paused all deployments, we're moving additional traffic off the affected infrastructure, and we're restarting affected servers to return them to service."
Microsoft also investigated why the servers were failing automated health checks. It said the problem could be linked to a component responsible for checking server health and that it had taken steps to prevent more servers from being affected.
Some affected servers return to service
In its latest update, Microsoft said it had tested an alternative method of checking server health, allowing some affected servers to return to service. The company was also preparing automated systems to identify and restart unresponsive servers.
It said:
"We've validated an alternative service health check method, which allowed a subset of affected servers to successfully return to service. We're now applying this change more broadly. We're also preparing automated recovery systems to continually detect and restart unresponsive servers, to maintain service stability while this change progresses."
Microsoft has not yet identified the exact reason behind the server health-check failures. It said it was continuing to work on restoring services and monitoring the affected systems.
Users can follow updates through the Microsoft 365 admin center under incident numbers EX1550543 and MO1550821, or at status.cloud.microsoft.
