What Exactly Broke?
Starting around 4 PM GMT on Thursday, November 12, users across the globe began reporting issues with key Microsoft 365 services. The outage primarily crippled Exchange Online, the cloud-based engine that powers Outlook email and calendars. This had a domino
effect, impacting other integrated tools like Microsoft Teams, where features such as calendar access and meeting scheduling failed. The disruption also hit Microsoft Copilot, the company's AI assistant, along with other services like OneDrive and Microsoft To Do. The outage was widespread, affecting users in at least 74 countries, from government agencies and airlines to small businesses and individual users.
The Technical Cause, Explained
In short, this wasn't a cyberattack. Microsoft has been clear that it has found no evidence of malicious activity. Instead, the problem stemmed from an internal issue with its own infrastructure. According to Microsoft's statements, the outage was triggered by a recent network configuration change that went wrong. This change caused a core process responsible for establishing secure connections to become overwhelmed on some servers. As a result, a number of servers became unexpectedly unavailable, which in turn strained the remaining infrastructure and caused them to stop handling requests. This cascading failure is what led to the widespread and lengthy disruption, which the company struggled to resolve as initial fixes did not hold under the returning traffic load.
The Global Impact
The consequences of the outage were felt immediately and globally. Government agencies in Australia, Japan, the United States, and Singapore reported disruptions. The UK's National Health Service (NHS) reported a 'serious impact,' with emergency call handlers unable to refer patient details through normal channels. Businesses were forced to find workarounds, with some organisations reportedly resorting to fax machines. European stock market operator Euronext advised companies to use the telephone to communicate corporate information. Airlines like Air India and Maersk warned customers of communication delays, and even AI companies like OpenAI and Anthropic faced issues with their Microsoft connectors. The event highlighted just how deeply intertwined modern business, government, and even healthcare operations are with a handful of major cloud providers.
Microsoft's Response and Recovery
Microsoft acknowledged the issue quickly and began providing updates via its service health status pages and social media. Engineers worked through the night to roll back the problematic configuration change and stabilize the system. The company described its efforts as a 'measured approach to identify and repair affected infrastructure'. By Friday, November 13, Microsoft reported 'encouraging recovery progress' across North America and Europe, with services slowly returning to normal. However, it cautioned that some users might still experience intermittent issues or email backlogs as the system capacity was gradually restored. The company has promised a full post-incident report that will provide more details on the root cause and steps to prevent a recurrence.
