Microsoft 365 Outage Knocks Out Outlook and Teams Worldwide
Microsoft 365 went down worldwide on Thursday, leaving workers unable to open their email, join meetings or reach shared files as one of the world’s most widely used office suites suffered a major failure.
Reports of trouble began at about 12.30pm Eastern Time on Thursday, and complaints on the tracking site Downdetector climbed rapidly. Reports about Outlook peaked at 138,058 at around 1pm Eastern, with roughly 97,000 of those coming from the United States, according to figures cited by Reuters. Downdetector also logged more than 38,000 reports for Microsoft 365 itself and about 4,500 for Teams.
The disruption hit at the start of the working day for millions of people and lasted for hours. By Thursday evening, Microsoft said it was still working to return affected servers to service, with only limited recovery visible as users gradually reconnected.
What went wrong
Microsoft said the main problem lay with Exchange Online, the cloud service behind Outlook email, calendars and contacts. In updates posted on X, the company said a large number of its servers had become unavailable after failing automated health checks, pushing extra load onto the servers that were still running.
The company stressed that the failure was not caused by a surge in traffic. It also said there was no indication of a cyberattack, a point a Microsoft spokesperson confirmed to ABC News.
Microsoft has not yet published a final root cause. It said it was reviewing diagnostic data, limiting traffic and rebuilding affected servers using a previous software configuration. The company has also paused deployments and configuration changes while it checks whether a recent update played a part.
Which services were affected
Email was hit hardest, but the outage spread well beyond Outlook. Microsoft’s service health page listed Exchange Online, Microsoft Teams, SharePoint Online, Microsoft 365 Copilot, Microsoft Defender XDR, Planner, To Do, Intune, Purview and Power BI as potentially affected.
The knock-on effects reached beyond Microsoft’s own products. OpenAI said it was investigating an issue with its Microsoft connectors, in which new connections could break and tools stop working as expected. Anthropic said it had identified an issue with an upstream provider affecting its Microsoft 365 connector.
Administrators can follow the incident in the Microsoft 365 admin centre under the references EX1550543 for Exchange Online and MO1550821 for the wider Microsoft 365 impact.
A slow recovery
Recovery has been gradual and uneven. Microsoft warned that servers returned to service could become unresponsive again once they received traffic, and that mailboxes might fail to open again before recovering on their own.
By Thursday evening, reports of Outlook problems had fallen to around 34,490, and Microsoft 365 reports had dropped to nearly 13,000, according to Downdetector. Teams had been restored in North America, according to the Associated Press, although some users were still reporting connection problems.
Mail sent to an affected organisation is normally queued and retried by the sender’s server, so delayed messages should arrive late rather than disappear entirely.
A reminder of how much runs on the cloud
The outage is the latest reminder of how much of everyday office work now depends on a small number of cloud platforms. When Exchange Online falters, email stops, calendars fail and the tools built on top of them — from Copilot to Teams meetings — go with it.
For businesses, the practical advice from Microsoft is simple: wait for capacity to return, and do not repeatedly retry connections, which only adds load to servers still recovering. IT teams should watch the two incident references above for the official all-clear.
Microsoft said it would continue restoring capacity region by region. Until it confirms full recovery, some users should expect errors, slow connections and delayed email.
