The primary technical cause, according to Microsoft’s investigation, was a process responsible for establishing secure connections on affected servers. This process became overwhelmed, causing servers to stop processing requests. Microsoft clarified that the issue was not driven by an overall increase in traffic, but rather by a reduction in the number of servers available to manage existing demand. To address the failure, the company is implementing a configuration change, testing it on a subset of servers before a wider rollout. Additionally, Microsoft is reversing a recent network configuration change that coincided with the start of the outage to determine if it contributed to the disruption.
Peak outage reports on Downdetector reached 138,058 at approximately 1:30 am on Friday, before falling to around 34,490 by 4:30 am. Times of India cited nearly 130,000 global user reports, aligning with the peak figures recorded by Downdetector. During the outage, Exchange Online users faced difficulties accessing mailboxes via web, desktop, and mobile applications, with significant delays in email delivery. Microsoft 365 users were unable to access recently used files, and some pages in the Microsoft 365 admin centre failed to load.
The disruption affected a broad range of Microsoft services. Microsoft Copilot users reported difficulties loading the chat interface or receiving responses, with its ability to access work-related data, including emails and calendars, interrupted. While Microsoft Teams maintained core messaging and online meeting capabilities, features dependent on Exchange Online, such as calendar management and meeting scheduling, were impaired. Other impacted services included Microsoft Planner, To Do, Defender, Purview, Graph, Fabric, Power BI, SharePoint Online, Universal Print, and Windows 365. Education features such as Assignments and Reading Progress were also disrupted.
The outage had tangible effects on businesses relying on Microsoft infrastructure. Workhorse Group, an electric truck maker, rescheduled its third-quarter results announcement from November 12 to November 16, citing business disruptions caused by the global Microsoft outage. Third-party AI providers were also affected; OpenAI stated it was investigating issues with Microsoft connectors that prevented new connections, while Anthropic identified an upstream provider issue affecting its Microsoft 365 connector.
Microsoft introduced temporary traffic restrictions in certain locations to stabilize the system. The company is currently monitoring affected servers to ensure they remain stable while handling fewer connections before gradually restoring additional traffic. Services that did not depend on Exchange Online continued to function throughout the incident. Microsoft has indicated that the configuration change is being tested and will be rolled out more widely as part of the remediation process.
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