Microsoft 365 Outage Hits Outlook and Teams Worldwide as Recovery Stalls

A worldwide Microsoft 365 outage that began on Thursday knocked out Outlook email, Teams and Copilot for users in dozens of countries, and Microsoft said on Friday that recovery was still uneven more than 12 hours after the disruption started.

The company first acknowledged the problem at about 12:54 p.m. Eastern time on Thursday, when its Microsoft 365 Status account said it was investigating reports of users unable to reach Exchange Online mailboxes “through multiple connection methods in the Americas”. Within the hour, Microsoft opened a wider advisory covering the whole Microsoft 365 suite.

What went down

Exchange Online, the cloud email service behind Outlook, was hit hardest. Microsoft also listed Teams, SharePoint Online, Microsoft 365 Copilot, Intune, Planner and To Do among the affected services, along with security and compliance tools including Defender XDR and Purview.

Outage tracker Downdetector recorded about 138,000 reports of Outlook problems in the United States at the peak, at around 1 p.m. Eastern on Thursday, according to Reuters. The Associated Press reported nearly 130,000 reports shortly after 1 p.m. Downdetector logged reports from users in 74 countries and territories within about an hour of the outage starting. The figures count user-submitted reports, not the total number of people affected.

The disruption reached well beyond office workers. Australia’s domestic spy agency, ASIO, and the Australian Federal Police were both affected, their chiefs confirmed at a news conference, according to Reuters. OpenAI and Anthropic also reported problems with their Microsoft 365 connectors, which let their AI tools interact with Microsoft services.

What Microsoft says caused it

Microsoft first blamed unusually high load on its infrastructure, then corrected itself. The company said the elevated load was not driven by more traffic, but by “a number of servers being unexpectedly unavailable”, which strained the systems still running. It later said a core process on the affected servers was becoming overwhelmed, causing capacity to fall away.

The company said the failing servers had dropped out after failing automated health checks, and that the failures “may originate from a specific component that’s responsible for processing server health”. It added that it had not identified any recent change linked to the start of the outage.

Microsoft said there was no indication of a cyberattack. Australia’s Home Affairs and Cyber Security Minister, Tony Burke, told a press conference that Microsoft believed it was not facing a cyberattack. A full root cause had not been published by Friday morning, and Microsoft said a preliminary post-incident review was expected within two business days.

Recovery stalls into a second day

Recovery proved harder than expected. Microsoft reported limited recovery by about 7 p.m. Eastern on Thursday, but in an update just after midnight UTC on Friday it said servers it had returned to service “can become unresponsive again once they receive traffic”. The company said it was temporarily limiting some types of traffic to the affected infrastructure and rebuilding a subset of servers using a previous configuration to test whether that stopped them failing.

By Friday morning, Microsoft had reported positive results from a patch applied to part of its infrastructure, according to The Guardian, but Reuters reported that the recovery remained partial and had not yet been sustained in all affected regions. At 2:30 a.m. GMT on Friday, Downdetector still showed more than 25,000 Outlook problem reports in the United States, according to Reuters.

The outage came hours after a separate, smaller Teams incident on Thursday morning. That incident, tracked as TM1550488, ran from 9:45 to 10:53 a.m. Eastern and affected users in North and South America. Microsoft attributed it to resource contention and said it was fully resolved; it has not said whether the two incidents are linked.

A familiar vulnerability

The disruption is the latest reminder of how much of daily work now runs through a handful of cloud platforms. When Exchange Online faltered, it took email, calendars, meetings and AI assistants with it — and because Defender XDR, the console many security teams use to detect and respond to threats, was also degraded, the outage doubled as a security event for some organisations.

For users, Microsoft’s advice during the outage was to watch its service health page and the Microsoft 365 Status account for updates, and to expect a gradual recovery as capacity returned. The company has given no time for full restoration, and the incident remains listed under references EX1550543 for Exchange Online and MO1550821 for the wider Microsoft 365 disruption.

Frequently asked questions

What caused the Microsoft 365 outage? Microsoft said servers became unexpectedly unavailable after failing automated health checks, overloading the remaining infrastructure. It was not caused by a traffic surge, and no full root cause had been published by Friday morning.

Which services were affected? Exchange Online and Outlook were hit hardest, along with Teams, SharePoint Online, Microsoft 365 Copilot, Intune, Planner, To Do, Defender XDR and Purview.

Is the outage over? Not fully. Microsoft reported progress on Friday after more than 12 hours of disruption, but said recovery remained partial and had not been sustained in all affected regions.