Microsoft's second day of service disruption continues to affect search and other functions across Microsoft 365, even as much of Exchange Online mail flow has recovered. The incident, which began with an investigation into Exchange Online problems at 11:55 a.m. UTC on August 31, has grown into a broader outage touching multiple services.
Timeline of the unfolding incident
At 12:33 p.m. UTC, Microsoft isolated a common failure pattern in Exchange Online requests related to authentication and protocol connectivity. About an hour later, the company identified a potential corrective action and was evaluating deployment. Another hour later, the problem extended beyond Exchange Online to other Microsoft 365 services, though not as a complete or total outage.
The official start time of the broader incident was recorded at 3:08 p.m. UTC. Microsoft attributed the root cause to "an issue within a core authentication configuration used by multiple Microsoft 365 services." At 4:36 p.m. UTC, Microsoft was re-examining recent changes and exploring ways to restore components, including potentially reverting an update.
Mitigation testing produced positive results at 5:55 p.m. UTC. By 6:40 p.m. UTC, Microsoft began implementing targeted mitigation to reapply core authentication components across a sample of affected infrastructure. Some users began to see recovery in certain impacted scenarios.
Services and functions affected
The outage has degraded a wide range of functions. Exchange Online connectivity and search were hit, as were SharePoint Online and OneDrive for Business search, file access, synchronization, and content loading. Teams search, calendars, and presence also suffered. Microsoft 365 Copilot prompts requiring Microsoft 365 data were degraded as well.
These services form the backbone of daily work for countless organizations. Enterprises rely on them for routine workflows and access to critical information. The disruption could delay routine business workflows and leave employees without access to critical information and tools until services are fully restored.
Recovery progress and persistent issues
Stay ahead of the AI curve
The most important updates, news, and content — delivered weekly.
No spam. Unsubscribe anytime.
By late Monday, Microsoft reported widespread recovery of Exchange Online mail connectivity. The company warned that some organizations could take longer to drain backlogged mail queues. After validating persistent recovery of mail flow across the environment, Microsoft shifted focus to restoring search functionality.
As of Tuesday, Microsoft continued working on search-related issues. The company has been restarting affected infrastructure and reapplying the authentication-component fix. The latest update at 2:39 a.m. UTC reported "yielded progress" with incremental improvement in service-health telemetry for search functionality across a sample of affected environment.
The recovery has not been uniform for all affected enterprise customers immediately. Partial recovery did not bring the broader incident to an end. The duration of the disruption remains uncertain as the incident enters its second day.
No estimated time for full resolution
Microsoft has not provided an estimated time for full resolution. The company said it would provide an estimated recovery timeline when one becomes available. This leaves many organizations in a holding pattern, unsure when full functionality will return.
The University of Pennsylvania's IT department published a report based on data from Microsoft's admin console detailing the incident timeline. That report helps clarify the sequence of events for those tracking the outage.
Microsoft expanded mitigation and began restarting targeted sections of infrastructure. The company continues to reapply the fix across affected systems. The authentication configuration issue at the heart of the problem is critical because multiple Microsoft 365 services depend on it for normal operation.
For now, the incident grinds on. Search functionality remains the primary unresolved issue, even as mail flow has largely stabilized. Organizations using Microsoft 365 will need to monitor the situation closely as Microsoft works toward a complete restoration.