Microsoft 365 Massive Outage – Fixes Fail as Restored Servers Keep Going Unresponsive

Microsoft has yet to find a fix that holds for the global Microsoft 365 outage, which has now run for more than 10 hours. Servers that engineers bring back online are falling over again as soon as user traffic reaches them.

The outage began on November 12, 2026, and continued through November 13. As we reported earlier, it started with Exchange Online mailbox access failures in the Americas. It then spread to Outlook, Teams, SharePoint, Copilot, and Microsoft Defender XDR users in any region.

Microsoft’s latest status updates show the recovery has stalled. The company says it is running several workstreams in parallel to “address our current blocker” and return parts of its infrastructure to a healthy state. It has given no estimated time for full restoration.

The incidents are tracked as EX1550543 and MO1550821 in the Microsoft 365 admin center.

Restored Servers Fail Again Under Load

The core problem is that restarting servers does not keep them healthy. In an update on its Microsoft 365 Status account, Microsoft said restored servers “can become unresponsive again once they receive traffic.”

Engineers are still analyzing diagnostic data to learn what triggers the behavior. Microsoft has not announced a root cause.

With restarts failing to hold, the company has moved to three fallback measures:

• Traffic limiting. Microsoft is temporarily restricting which types of traffic can reach the affected infrastructure in some locations.
• Server rebuilds. A subset of affected servers is being rebuilt on a previous configuration, to test whether that stops them from going unresponsive.
• Traffic rerouting. Engineers are adjusting traffic protocols, redistributing load, and applying what Microsoft calls strategic traffic blocking.

Microsoft says it sees partial recovery in regions where these traffic measures are in place. Partial recovery is not stable service, and users in those regions may still see intermittent failures.

The rebuild on a previous configuration is the notable step. It suggests Microsoft suspects a recent change, though it has not confirmed one as the cause.

Microsoft says it is seeing positive results from efforts to restart affected infrastructure and restore server availability amid the ongoing Microsoft 365 service disruption. The company is recovering impacted infrastructure in an isolated manner and closely monitoring performance to confirm stability before expanding restoration efforts more broadly.

Following these initial recovery efforts, Microsoft expects service availability to improve gradually as the restoration process expands across the affected infrastructure. Administrators can track further updates under incident IDs EX1550543 and MO1550821 in the Microsoft 365 admin center or through Microsoft’s alternative status update link.

How the Outage Unfolded

Microsoft first blamed elevated load across multiple regions. It later corrected that view: traffic had not increased, but a number of servers had unexpectedly dropped out, straining the rest.

The servers were failing automated health checks, which decide whether a machine can take requests. Engineers paused all deployments, moved traffic to other parts of the worldwide infrastructure, and restarted the affected servers.

Those steps did not work. Microsoft admitted its actions had “not provided the anticipated relief” and found that a core process on the servers was being overwhelmed.

An alternative health check method brought some servers back, and they appeared stable at first. The latest updates confirm that stability did not last once traffic returned.

Scale of the Impact

Downdetector logged more than 120,000 Outlook problem reports at the peak, and reports came from 74 countries. Report volumes have since fallen as partial recovery took effect.

Microsoft’s service health page lists Exchange Online, Teams, SharePoint Online, Microsoft 365 Copilot, Defender, Planner, To Do, Intune, Purview, and Power BI among the affected services. Features that do not depend on Exchange Online reportedly kept working.

The disruption also reached third parties. OpenAI and Anthropic both reported problems with their Microsoft 365 connectors. Electric truck maker Workhorse Group postponed its third-quarter results to November 16.

Microsoft says the outage is not the result of a cyberattack. Executive Vice President Charles Lamanna confirmed it was not caused by a security breach, Business Standard reported.

What Administrators Should Do

The fault sits in Microsoft’s infrastructure, so local troubleshooting will not restore service. Administrators should:

• Track MO1550821 and EX1550543 in the Microsoft 365 admin center, or use status.cloud.microsoft if the admin center will not load.
• Avoid resetting passwords, rebuilding Outlook profiles, or changing tenant settings in response to the errors.
• Expect intermittent access even in regions showing recovery, since Microsoft is deliberately blocking some traffic types.
• Warn users about phishing emails and fake support calls that exploit the outage.
• Plan for delayed mail delivery once service returns and queued messages are processed.

We will update this story as Microsoft shares more on the root cause and recovery.

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