A global outage of Microsoft 365 services disrupted communications across finance, aviation, healthcare and government sectors this week. The disruption began around midday Eastern Time on November 12 and persisted for roughly 12 to 18 hours, affecting users in at least 74 countries and territories.
What Failed and Why
Exchange Online, the backend powering Outlook email, took the hardest hit, with mailboxes delayed or inaccessible. The outage also affected Teams, Copilot, SharePoint, OneDrive and Defender XDR, which experienced connectivity problems or degraded performance. Downdetector logged peak issue reports exceeding 130,000 for Outlook alone. Microsoft 365 has an estimated user base of over 430 million globally.
Microsoft traced the problem to a technical issue in which servers failed automated health checks while under elevated loads. The company stated the outage was not caused by a cyberattack or by problems with AI.
Finance Returns to Older Methods
Financial institutions adapted quickly using analog communication methods. Euronext, the European exchange operator, directed listed companies to contact it by phone while verifying callers' identities. Trading desks in Taiwan and Japan turned to faxes to confirm trades. Telephones, faxes and even Bluetooth file transfers filled communication gaps across the sector.
Most institutions reported that their core trading and operational systems continued functioning. The outage affected the communication layer surrounding those systems rather than the systems themselves.
Broader Impact
Airlines, health services and police forces experienced disruptions. Some companies postponed earnings releases or customer updates because they could not reliably distribute communications during the outage.
The Consolidation Risk
Many organisations rely on a single provider for email, messaging, document storage, security tools and AI assistants. This arrangement reduces management costs and complexity but creates a single point of failure that can cascade across industries. Organisations with backup communication protocols—such as Euronext's phone verification process—weathered the disruption more effectively than those without fallback systems in place.
