Microsoft experienced a widespread service disruption on Thursday, affecting several of its platforms, including Outlook, Teams, Copilot and Microsoft 365, with tens of thousands of users reporting difficulties accessing their accounts and using the company's applications.
Outlook was among the worst-affected services, with outage-tracking website Downdetector recording a peak of more than 130,000 reports shortly after 1pm ET. The number of complaints subsequently declined, but thousands of users continued to report difficulties loading their inboxes and sending or receiving emails.
The disruption, which lasted for several hours and continued for around 10 hours, affected businesses and government agencies across multiple countries. Users in India, Australia and Japan also reported problems. Thousands of complaints were registered against Microsoft Teams, the company's workplace messaging platform, and Copilot, its artificial intelligence assistant. Other Microsoft 365 services were also affected.
Microsoft identifies server failures behind disruption
Microsoft acknowledged the disruption and said it was investigating issues affecting its email and Teams applications.
In updates shared on social media, the Redmond, Washington-based technology company said it was aware of users experiencing difficulties accessing Exchange Online mailboxes through multiple connection methods in the Americas. It subsequently warned that the disruption could affect Microsoft 365 connectivity in any region.
The company initially attributed the connectivity problems to elevated load across a portion of its infrastructure. However, further investigation indicated that the increased load was not caused by a surge in user traffic but by several servers becoming unexpectedly unavailable.
Microsoft said the affected servers had failed automated health checks, placing additional pressure on the remaining operational infrastructure. The company did not immediately establish what had triggered the failures.
To address the problem, Microsoft began redistributing connection traffic across its worldwide infrastructure and restarting affected servers. It also paused deployments and configuration changes as a precaution while examining whether any recent changes were linked to the incident.
"We're aggressively pursuing all pathways to reduce impact," the Microsoft 365 Status account said in a post on X.
The company later said it had validated an alternative method for conducting server health checks, allowing some affected servers to return to service. However, recovery was slower than expected, with Microsoft reporting capacity and traffic-management imbalances.
It also warned that some servers could become unresponsive again when they received traffic. The company therefore restricted certain types of traffic reaching affected infrastructure in some locations while continuing restoration efforts.
Teams partially restored, users continue reporting problems
Earlier on Thursday, Microsoft said it had successfully restored the issues affecting Microsoft Teams in North America. However, some users continued to report connectivity problems despite the announcement.
The company subsequently reported limited recovery as affected servers were brought back online and users gradually reconnected to its services. Downdetector recorded around 34,490 reports of Outlook problems by approximately 6pm ET, down from the peak of more than 138,000 reports.
The disruption also affected connectors used by artificial intelligence services operated by OpenAI and Anthropic. Government operations in Australia and the United States were among those affected, with the US House of Representatives also reporting disruption. Australia's cyber security minister said Microsoft believed the incident was not the result of a cyberattack.
The outage highlighted the dependence of businesses and government organisations on Microsoft's cloud-based email and workplace productivity services. The company did not initially provide a definitive timeline for the complete restoration of all affected platforms.