REDMOND, United States – A widespread Microsoft 365 outage disrupted access to Outlook, Microsoft Teams, Copilot and other cloud-based services on Thursday, November 12, affecting users across multiple regions and interrupting business communications and workplace operations.
The disruption continued into Friday, November 13, as Microsoft worked to restore affected infrastructure. Users reported problems accessing email accounts, loading inboxes, sending and receiving messages, scheduling meetings and connecting to Microsoft applications.
Other affected services included SharePoint Online, OneDrive, Microsoft Defender XDR, Planner, To Do, Intune and several Microsoft Purview services. Some Power BI users also experienced difficulties exporting reports containing sensitivity labels.
Downdetector recorded nearly 130,000 reports of Outlook-related problems at the height of the disruption. These figures represent user-submitted reports rather than a confirmed count of affected customers.
Microsoft identifies server availability problems
Microsoft initially reported connectivity problems involving Exchange Online, the cloud infrastructure supporting Outlook and other Microsoft 365 applications.
The company subsequently identified elevated infrastructure loads across multiple regions as a contributing factor. Its investigation found that numerous servers had unexpectedly become unavailable, shifting additional demand onto the remaining infrastructure.
Microsoft said the elevated load was not caused by an overall increase in customer traffic but by the loss of server capacity.
The company began redistributing connections across its global infrastructure, moving traffic away from affected systems and restarting servers to restore capacity.
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Microsoft also paused deployments while engineers investigated the underlying problem and tested alternative methods of returning affected servers to service.
Recovery efforts produce limited improvements
In updates published on Friday, Microsoft said it had returned a portion of the affected servers to service and observed limited recovery.
However, the company warned that some restored servers became unresponsive again when they began receiving customer traffic. Engineers were examining diagnostic information to identify what triggered the behaviour.
Microsoft also temporarily restricted certain types of traffic reaching affected infrastructure in selected locations to help stabilise the recovery process.
The company said it was rebuilding some affected servers using an earlier software configuration to determine whether this would prevent further failures. It planned to expand the approach if the tests produced stable results.
Microsoft cautioned that users could experience gradual service recovery as applications and devices reconnected to restored infrastructure.
Business and AI services also affected
The disruption extended beyond Microsoft’s traditional productivity applications.
Microsoft 365 Copilot users reported difficulties loading the AI assistant and receiving responses. Some Copilot functions that rely on access to workplace information, including email, calendars and files, were also affected.
The outage also affected connectors used by OpenAI and Anthropic to access Microsoft 365 services. OpenAI said it was investigating problems involving Microsoft connectors, while Anthropic identified an issue with an upstream provider affecting its Microsoft 365 connector.
The disruption demonstrated how failures in shared cloud infrastructure can affect organizations and services that depend on Microsoft’s systems, including third-party applications.
Microsoft says no indication of cyberattack
Microsoft said it had no indication that the outage resulted from a cyberattack. Its investigation focused on server availability, infrastructure capacity and the technical processes involved in restoring affected systems.
The company had not provided a definitive explanation for why the servers became unavailable in the updates reviewed for this report.
The incident was tracked under Microsoft’s service-health advisories, including EX1550543 for Exchange Online connectivity problems and MO1550821 for the wider Microsoft 365 disruption.
The company continued working to restore services as users and organizations awaited a stable return to normal operations.
Primary Sources: Microsoft 365 Service Health, incident MO1550821, November 12–13, 2026: identifies the affected Microsoft 365 services, describes elevated infrastructure load, unexpected server unavailability, traffic redistribution, server restarts and incremental recovery measures; Microsoft Exchange Online service advisory EX1550543, November 12–13, 2026: documents mailbox connectivity problems affecting Outlook access through web, desktop and other connection methods; Microsoft 365 Status, public service updates, November 13, 2026: reports the company’s investigation and recovery efforts, including the return of some servers to service, traffic restrictions and testing of alternative server configurations. Microsoft’s statement that it had no indication of a cyberattack was documented in its response to contemporaneous reporting. The complete internal technical investigation and final root-cause report were not publicly available in the material reviewed.
