Downdetector, which tracks user-submitted problem reports, logged around 110,449 complaints about Outlook by 12:02 a.m.
Impact Spreads Beyond Email
The disruption spread well beyond email. Microsoft’s admin-center advisory (MO1550821) warned that customers might be unable to connect to Exchange Online, Teams, SharePoint Online, Microsoft 365 Copilot and Defender XDR. Microsoft later said the problem could affect Microsoft 365 connectivity in any region, and its own status page struggled to load at times.
What Microsoft Says Went Wrong
Microsoft’s explanation was that part of its infrastructure was under unusually heavy load across multiple regions, which it linked to a number of servers becoming unexpectedly unavailable. It said it paused all deployments, moved traffic off the affected systems and began restarting servers. A separate Teams problem that hit North and South America earlier in the day was fixed, Microsoft said, though it has not said whether the two incidents are connected.
Recovery Comes in Fits and Starts
Around 4 p.m. ET, Microsoft said it had validated an alternative way of running service health checks that brought some servers back, and it began applying the change more widely. By about 6 p.m., it reported that a portion of servers had returned and were stable, but warned they could become unresponsive again once traffic hit them. Shortly after 10 p.m., it said recent changes were “not taking as expected” and that engineers were looking for other ways to add capacity.
As of the latest reports available, Microsoft had not publicly named a root cause or suggested a cyberattack. The company also had not given a time for full restoration, saying users should expect a gradual recovery as their apps reconnect.
Public Services and Markets Feel the Effects
The impact reached public services. New York City’s emergency management department warned residents of possible delays in email delivery and responses from city agencies and advised calling 311 for non-emergency matters and 911 for emergencies. Amazon Web Services told CNBC it was operating normally despite some inaccurate outage reports. Microsoft shares closed Thursday roughly flat, at around $523, according to Deadline.
It is not the first rough stretch for the service this year. In January, there was a nine-hour outage of Microsoft 365 service which, according to The Register, resulted from one part of the North American infrastructure not routing its traffic correctly.
Note: This is a developing story. Microsoft’s service health updates will carry the latest status.
