Microsoft said Friday afternoon that a global outage affecting its suite of workplace products, most notably its Outlook email service, was caused by a bug introduced during a network capacity upgrade.
“We have addressed the underlying issue and continue to restore service to remaining customers and regions,” Microsoft said in a statement. “Given the scale of demand, we restored services gradually, validating stability at each stage. While this took longer, it helped ensure a stable restoration.”
Earlier Friday, the company had already ruled out a hack, but in its latest statement, it definitively said the disruption in service was not caused by cyberattacks or meddling from AI agents.
Microsoft said it would provide a full report on the root cause once it completes an internal investigation.
“We are deeply sorry for the disruption this incident has caused our customers and partners. We know the trust they place in our services and take that responsibility extremely seriously. We are seeing broad recovery and stability across our services,” Microsoft said.
The ability to send and receive emails with Outlook began returning for some users as early as Friday morning.
The disruption began Thursday afternoon and crippled Exchange Online, the underlying engine that powers Microsoft’s email infrastructure. This hampered everyday operations for major businesses and millions of users worldwide.
In morning service updates at 6 a.m. and 7 a.m. ET, Microsoft said it was seeing recovery progress across Europe and the Asia Pacific region, noting that Japan remained “comparatively more stable.”
Services in North America were also improving by 7 a.m., though the company cautioned at the time that “some users may still experience intermittent issues as recovery actions continue.”
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Microsoft said it extended its email timeout window to 48 hours to protect delayed messages while services recover. Normally, if an email cannot be delivered within a standard window, mail servers give up and bounce the message back to the sender.
That gives emails caught in the backlog since the outage began Thursday afternoon until at least Saturday afternoon to reach recipients once systems recover.
Outlook, of course, is used for far more than email. Users had reported disruptions to key scheduling and productivity tools. This included viewing calendars, sending meeting invites or editing existing events.
Beyond Outlook, the disruption is affecting Microsoft’s broader workplace suite, preventing some users from viewing recently used files in apps like Word, Excel and PowerPoint, while blocking external file sharing in SharePoint Online.
Copilot, Microsoft’s AI assistant integrated across Microsoft 365, was also heavily disrupted — leaving users unable to load chats, generate responses or pull data from their emails, calendars and files.
The outage didn’t just sideline individual users; it also hamstrung major corporations. Indian airlines IndiGo and Akasa Air both reported problems with their customer-support email systems, while Air India has temporarily rerouted its email services.
Leading artificial intelligence firms OpenAI and Anthropic were also swept up in the worldwide failure, with both companies reporting issues with their Microsoft 365 integration tools Friday morning. Anthropic and OpenAI said Friday afternoon those issues were beginning to subside.
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