How one network change disrupted Microsoft Outlook, Teams & AI tools that rely on them

A financial firm in Taiwan reverted to using faxes to confirm trades, while Europe’s Euronext exchange experienced email disruptions. Shipping company Maersk informed customers that updates might take longer. These were just a few of the thousands of businesses affected by a Microsoft outage that began on November 12 and persisted for over a day.

The technology giant had altered something within its network, which led to a trading desk resorting to using a fax instead. Microsoft traced the incident to a problem that emerged after an earlier network expansion. They dismissed the notion of a cyberattack and ruled out AI as a contributing factor. The public updates from Microsoft described servers dropping out of service, the reasons behind a few failures re-emerging after restarts, and how the email system's issues cascaded to applications beyond Outlook.

Microsoft announced that the Microsoft 365 outage, which incapacitated Outlook, Teams, and Copilot for over 24 hours, had been resolved. During the incident's final status update, the company affirmed, "We have completed our efforts to address the underlying issue of the incident and restored service." The disruption impacted users in at least 74 countries, forcing businesses, governments, hospitals, and airlines to fall back on phone lines, paper records, and, in some offices, even fax machines.