Microsoft 365 outage disrupts Outlook and Teams worldwide; company rules out cyberattack
Users struggled to send email and join meetings for many hours from Thursday into Friday after a large number of Microsoft servers became unavailable and failed automated health checks.
A prolonged outage of Microsoft's cloud services disrupted Outlook, Teams and other Microsoft 365 apps for users around the world from Thursday, 12 November, into Friday, 13 November, before the company said email delivery was approaching normal levels.
The problems began at around 12:30 pm to 1 pm US Eastern Time on Thursday, which was late night in India, TechRadar reported. Outage tracker Downdetector logged about 120,000 simultaneous reports in the US at the start, with Outlook complaints peaking above 131,000, and users in at least 74 countries were affected, according to TechRadar.
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What went wrong
Microsoft said a large number of servers had unexpectedly become unavailable, shifting the load to the remaining infrastructure even though overall traffic had not increased, SecurityWeek reported. A process that sets up secure connections became overwhelmed, and the affected servers began failing automated health checks and stopped handling requests.
The disruption started with Exchange Online mailboxes in the Americas but spread to Teams, SharePoint Online, Microsoft 365 Copilot and the Defender XDR security service. On Friday, Microsoft said the problem stemmed from an issue during an earlier network capacity upgrade that surfaced after a recent network change, TechRadar reported.
The company said there was no sign of malicious activity. It described the event as a technical issue not related to cyber activity or AI agents, and apologised to customers and partners.
Recovery
Engineers restarted affected servers, rolled back a network configuration change and moved to an alternative method of running health checks, according to SecurityWeek and TechRadar. Microsoft also extended Outlook's email timeout window to 48 hours so delayed messages would not be lost. By late Friday morning US time, it said email queues were approaching normal and most users were close to full service.
Microsoft has said it will publish a full post-incident report with the root cause once its review is complete.
Why it matters
Microsoft 365 is widely used by Indian companies, government offices, universities and IT services firms that work with overseas clients, so an outage that runs through the Indian night and into the working day can delay email and meetings. An industry analyst quoted by TechRadar said such incidents highlight how hard it is for businesses to switch quickly to a backup service when one cloud provider fails.
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