Microsoft Explains What Caused the Massive Outage That Knocked Down Outlook, Exchange & Other 365 Services for Hours

Microsoft has finally explained what exactly knocked down its services during the massive outage that lasted over twelve hours. The company says a network capacity upgrade introduced the underlying issue, which surfaced after a more recent network change. Microsoft has also ruled out cyberattacks and AI-related activity, confirming that services are now seeing broad recovery.

Microsoft traces outage to an earlier network capacity upgrade

In an official statement posted on X last night, Microsoft apologized to customers and partners for the disruption. The company said it takes the trust placed in its services extremely seriously.

According to the company, the problem originated during an earlier network capacity upgrade. It surfaced following a subsequent network change, eventually disrupting services across Microsoft’s ecosystem.

Microsoft says it has addressed the underlying issue. It is now working to restore access for customers and regions that are still experiencing problems.

Why Microsoft’s recovery took so long

Microsoft also explained why restoring services took longer than expected. Given the scale of demand, the company chose to restore services gradually instead of bringing everything back simultaneously.

Each recovery stage involved checking service stability before moving forward. Microsoft acknowledged that this approach extended the restoration process. However, it believes the slower recovery helped prevent further instability.

The disruption affected Microsoft’s broader service ecosystem, including Exchange Online, Outlook, Teams, and other Microsoft 365 services. Users had reported login failures, delayed emails, and problems accessing essential workplace tools.

The company says it is now seeing broad recovery and stability across its services. That said, some customers and regions still require restoration work.

Microsoft promises a full post-incident report

Interestingly, this statement also addresses concerns about whether the outage involved malicious activity. Microsoft explicitly ruled out cyberattacks and AI-related causes. This comes as AI-powered services and agents become increasingly integrated into its products.

The company has promised to publish a full post-incident report once its internal review is complete. That report should provide more details about the network change, the capacity upgrade, and why the issue affected so many services.

For now, Microsoft says the underlying problem has been addressed. But the extended disruption raises questions about how network changes are tested before reaching critical services. Microsoft’s upcoming incident report will likely explain why this issue took so long to contain. If you were affected by the massive outage, you might be able to get some amount as compensation. You can read our separate report on how to claim it.