A Microsoft 365 outage disrupted Outlook and some Microsoft Teams features on Thursday, 12 November, leaving businesses and public agencies struggling to access email and calendars. Microsoft reported limited recovery as it worked to bring affected servers back online. The company had yet to confirm full restoration in the updates reviewed on Friday morning.
What stopped working
The disruption centred on Exchange Online, the cloud service that handles email and calendars for many organisations. Some users could not open their mailboxes through Outlook on the web or desktop, while others experienced delays sending or receiving messages. In Teams, features that rely on Exchange Online, such as calendar access and meeting invitations, could fail even when core chat and calls remained available.
Microsoft also listed some SharePoint and Microsoft 365 Copilot features among those affected. Reuters reported that Downdetector logged more than 130,000 US Outlook problem reports at the peak, at around 6pm GMT on Thursday. That is a count of submitted reports rather than a tally of unique users affected. Problems were also reported in Australia, India and Japan.
Why recovery took time
Microsoft said some servers had unexpectedly become unavailable, putting more strain on the rest of its infrastructure even without an increase in overall traffic. The company found that a process responsible for establishing secure connections was becoming overwhelmed. Some servers that appeared healthy after a restart stopped responding again when connections returned.
Microsoft rerouted traffic, restarted affected infrastructure and began reversing a recent network configuration change that coincided with the start of the disruption. It was still assessing whether that reversal would help. Microsoft said there was no indication of malicious activity.
Businesses and public services felt the impact
The US House of Representatives and Australian government agencies were among the organisations affected, Reuters reported. Electric truck maker Workhorse Group postponed its quarterly results announcement, citing disruption from the outage. OpenAI and Anthropic also reported errors in their Microsoft 365 connections, showing how a problem with work email and calendars can spill into tools operated by other companies.
What this means for users
A working Teams chat or SharePoint file library does not necessarily mean Outlook or calendar access has recovered. Organisations can check Microsoft 365 Service Health for incident MO1550821 and the Exchange Online incident EX1550543. The wider lesson is practical: keep an agreed backup channel for urgent messages if email, calendars and collaboration tools depend on the same provider.
Sources
Microsoft 365 service health dashboard
Microsoft incident notices reproduced by the University of Pennsylvania
Reuters reporting on the outage and affected organisations
The Guardian reporting on recovery and the configuration rollback
OpenAI status update on Microsoft 365 connector errors
Anthropic service status and connector updates
