Microsoft Tests Fix for Multi-Hour Outlook and Exchange Online Outage

1 September 2026 · Source balance: Centre

On August 31, 2026, Microsoft experienced a widespread outage affecting Outlook and Exchange Online that lasted several hours. The disruption began around 11:30 AM ET, with thousands of users reporting email delays, failed message delivery, and authentication errors. By 2 PM ET, Downdetector recorded over five thousand user complaints. Microsoft identified the root cause as an issue with an authentication component within Exchange Online services. The company developed a remediation strategy and began testing it on a portion of its infrastructure to verify the fix would work before deploying it more broadly. The company also confirmed the authentication issue affected other Microsoft 365 services beyond email. While Microsoft worked to restore service through its cautious staged approach, the outage highlighted the critical role email plays in business operations and the vulnerability of cloud-based services when centralized infrastructure fails.