Microsoft says the Microsoft 365 outage that disrupted Outlook, Teams and Copilot for more than 24 hours is now fixed. In its final status update on the incident, the company said, “We have completed our efforts to address the underlying issue of the incident and restored service.” The disruption hit users in at least 74 countries and left businesses, governments, hospitals and airlines falling back on phone lines, paper records and, in some offices, fax machines.The trouble began on November 12, when users in the Americas reported they could not open their Exchange Online mailboxes. Microsoft first acknowledged the issue at 5:54 pm GMT (11:24 pm IST). Just 13 minutes later, it warned that users in any region could be affected. The company has since said it is “deeply sorry” for the disruption and maintains the incident was not caused by a cyberattack or AI.
Microsoft blames an earlier network upgrade for the Outlook outage
According to a Microsoft spokesperson, the incident “was introduced by an issue during an earlier network capacity upgrade that surfaced following a recent network change.” The company called it “a technical issue not related to cyber or AI/agents.”That explanation came after a long night of trial and error. Microsoft’s first updates on X blamed “elevated load” across several regions. Hours later, it said traffic had not gone up at all. A number of servers had become unexpectedly unavailable after failing automated health checks, and their workload landed on the servers still running, straining those too.Engineers eventually traced part of the problem to a core process on the affected servers that handles secure connections. It was getting overwhelmed, and the servers stopped processing requests. At one stage, Microsoft admitted its actions “have not provided the anticipated relief.”
Why Outlook and Teams took almost a full day to recover
The hardest part was keeping servers up once they were back. Microsoft said servers it returned to service could stop responding again once they started receiving traffic. Its engineers worked on several fronts at once. They limited the types of traffic hitting affected infrastructure, rolled some servers back to an earlier configuration, patched an authentication and routing component and added virtual machines for extra capacity.Email made the job slower. Mail servers outside Microsoft keep retrying messages they could not deliver, so restored servers faced a backlog of queued mail the moment they came online. To make sure messages sent during the outage were not lost, Microsoft extended its email timeout window to 48 hours.“Given the scale of demand, we restored services gradually, validating stability at each stage. While this took longer, it helped ensure a stable restoration,” the company said.Asia Pacific was among the first regions to stabilise on November 13, followed by Europe and North America. By the afternoon of November 13 (GMT), Microsoft said email queues were “significantly reduced and approaching normal levels.” Teams chats and meetings had largely come back earlier, though calendar features that rely on Exchange Online stayed patchy for longer. Outlook.com, OneDrive, OneNote and Microsoft To Do, used on personal accounts, were hit as well.
Airlines, hospitals and courts in at least 74 countries felt the Microsoft outage
Microsoft said in January it had more than 450 million paid commercial subscriptions to its 365 services. That reach showed in who got hit.In India, the outage hit email support at IndiGo and Akasa Air. Air India rerouted its emails to keep receiving customer messages, and its flights ran as usual. At one large Indian brokerage, a backup covered for Outlook, but client calls on Teams were harder to manage.In the UK, NHS staff switched to paper records, pharmacies warned of prescription delays and a judge in Manchester sent jurors home. In Colorado, a sheriff’s office had to ask people to post bond in person, since online payments relied on Outlook email notifications. Some companies in Japan went back to fax. Even OpenAI and Anthropic ran into problems with their Microsoft 365 connectors, while electric truck maker Workhorse Group pushed its quarterly results to November 16.Investors were far calmer. Microsoft shares traded largely flat on November 13, even as the outage stretched into a second day.For users, a few loose ends may remain. Emails held in queues carry the time they were delivered rather than sent, so a message stamped November 13 may well have been written on the night of November 12.Microsoft has promised a full post-incident report once its review is complete. That report should spell out how a capacity upgrade knocked servers offline across regions for more than a day, and what the company is changing so the next network update does not do the same.