Microsoft confirmed Thursday that a large number of servers unexpectedly became unavailable, causing widespread disruptions to Outlook, Microsoft 365, and Teams for users across the Americas and potentially other regions. The issue, which began around noon Eastern Time, prompted over 130,000 user reports on outage tracker Downdetector and affected services including Exchange Online, SharePoint Online, Copilot 365, and Defender XDR.
Microsoft’s response and technical details
Microsoft stated in updates on X that the elevated load across its infrastructure was not due to increased traffic but rather the unavailability of a significant portion of servers. The company paused all deployments, moved additional traffic off the affected infrastructure, and initiated restarts of impacted servers to restore service. By late afternoon, Microsoft reported it was testing a configuration change to address servers failing automated health checks.
The company first acknowledged the issue at 12:50 p.m. ET, noting reports of users experiencing problems accessing Exchange Online mailboxes through multiple connection methods in the Americas. A follow-up update at 1:35 p.m. ET confirmed that a portion of infrastructure was experiencing elevated load across multiple regions, contributing to connectivity errors. Microsoft later clarified that the elevated load stemmed from servers becoming unexpectedly unavailable, straining remaining infrastructure.
Scope and impact on users
Downdetector recorded more than 130,000 reports of Outlook issues by 1:15 p.m. ET, with additional reports of problems accessing Microsoft 365 and Teams. Users reported difficulties sending and receiving emails, loading inboxes, and accessing other Microsoft services. The disruption also affected Microsoft’s own service status page, which failed to load for some users attempting to check for updates.
The outage extended beyond email services, impacting Microsoft Copilot, OneDrive, and Teams. OpenAI and Anthropic reported issues with Microsoft connectors, with OpenAI stating it was investigating broken new connections and tools not working as expected. Anthropic identified an issue with an upstream provider affecting its Microsoft 365 connector.
Regional and service-specific breakdown
Microsoft initially confirmed the issue was limited to the Americas but later stated the problem may affect Microsoft 365 service connectivity for users in any region. The company’s updates referenced incident EX1550543 in the Microsoft 365 admin center for further details. By early evening, reports indicated the outage had largely stabilized, though some users continued to experience intermittent issues.
Expert analysis on root cause
Tech expert Mark Gregory, an associate professor at RMIT, suggested the outage may have resulted from a misconfiguration during recent updates, possibly involving BGP or another network configuration problem. He noted that in cloud services like Outlook, which serves millions of users, a large number of servers are spread across the world. Gregory theorized that a significant portion of these servers may have "fallen off the network," leaving the remaining infrastructure unable to handle the load.
Microsoft did not immediately respond to requests for additional technical details on the root cause beyond its public updates. The company continued to provide periodic updates on X as it worked to safely return affected servers to service.