Microsoft 365 outage explained: cause, who was hit and what next

Microsoft said on Saturday (14 November) that all services were fully restored after a global Microsoft 365 outage that began on Thursday and lasted more than 24 hours. Here is what happened, what Microsoft says caused it and who was affected.

What happened? Reports of problems with Outlook, Teams and Copilot began climbing around 1725 GMT on Thursday (12 November), which is about 10.55 pm in India, according to Ookla, the parent company of Downdetector. Microsoft said the outage hit features tied to Exchange Online, its cloud email and scheduling service, while applications not connected to it kept working. Downdetector logged more than 7.4 million reports worldwide, peaking at nearly 20,000 a minute, over 1,500 times the normal level. Outage reports came from more than 70 countries. Reuters called it one of the longest in Microsoft's history.

What was actually down? Users could not send or receive email or manage calendars, and some Teams features tied to calendars were affected, while joining meetings and chats largely kept working, Gadgets Now reported. Copilot struggled to fetch information from work emails, calendars and files. Organisations that run Microsoft's software on their own servers, instead of the cloud, were somewhat spared.

Why did it happen? Microsoft said the problem came from an issue introduced during an earlier network capacity upgrade, which surfaced after a recent network change. In its timeline, reported by the BBC, a number of servers failed automated health checks and became unavailable, which put strain on the rest of the infrastructure. When engineers returned servers to service, they could stop responding again once traffic came back. Microsoft said it restored service gradually because of the scale of demand.

Was it a cyberattack? No, according to Microsoft. It called the problem a "technical issue not related to cyber or AI/agents" and said it was "deeply sorry". It also said there was no sign of malicious activity.

Who was affected? Government agencies in Singapore, Australia, Japan, the United States and the UK, including the NHS and London's Metropolitan Police, reported disruption, according to Reuters and the BBC. Indian airlines IndiGo, Akasa Air and Air India said their email support services were affected. Euronext reported email disruption, Aviva activated backups for its earnings calls and Maersk warned customers of delayed updates. One Taiwanese financial firm used fax to confirm trades, Reuters reported a source as saying.

What does it cost, and what next? Morningstar DBRS estimated global insured losses at between US$300 million and US$500 million, below the US$400 million to US$1.5 billion it cited for the 2024 CrowdStrike outage. Microsoft has promised a full post-incident report after its review. Reuters noted that this was not the first Microsoft 365 outage of 2026, after one in January and an Azure outage last month, and that analysts said repeated failures give IT departments a reason to think twice about relying on a single provider.