Microsoft is investigating a Microsoft 365 outage affecting Exchange Online, OneDrive for Business, SharePoint Online, Microsoft Teams, Microsoft Purview and Microsoft Defender XDR.
The incident was acknowledged on August 31 after users began reporting Exchange Online problems on social media and administrator forums. Microsoft has since traced the disruption to issues involving a core authentication configuration used by multiple internal services within the Exchange Online infrastructure.
Engineers began manually testing individual servers and resetting configurations to determine whether the changes would resolve the issue. Microsoft is tracking the wider Microsoft 365 incident under MO1465074.
As of early September 1, Microsoft said mailbox connectivity had been restored, roughly 12 hours after the outage was first acknowledged. Search functionality across affected services was still recovering, with Microsoft reporting improvement in its service telemetry as recovery work continued.
Why It Matters: Exchange Online supports business email for Microsoft 365 customers, but the expanded scope of the incident means organizations may also have experienced problems across collaboration, file storage, security and compliance services. While mailbox connectivity has been restored, the continued recovery of search functionality means some users may still encounter service limitations.
- Microsoft Identified an Authentication Configuration Issue: The company traced the outage to problems with a core authentication configuration used by multiple internal services within Exchange Online. Engineers performed manual server-level tests and configuration resets as part of the recovery effort.
- The Outage Extended Beyond Exchange Online: Microsoft later confirmed that OneDrive for Business, SharePoint Online, Microsoft Teams, Microsoft Purview and Microsoft Defender XDR were also affected. The incident is being tracked under MO1465074.
- Mailbox Connectivity Has Been Restored: Approximately 12 hours after first acknowledging the outage, Microsoft said mailbox connectivity had recovered. Users should once again be able to connect to their mailboxes following the earlier Exchange Online disruption.
- Search Functionality Is Still Recovering: Microsoft reported improvement in telemetry associated with search functionality early September 1 but said recovery actions were continuing as it monitored the services for widespread remediation.
- Reports Indicated Significant Customer Impact: Downdetector recorded tens of thousands of Outlook problem reports. Receiving messages was the largest category in the supplied snapshot, accounting for 37% of reports, while users also reported trouble with the Outlook app and website.
- This Follows Other Exchange Online Problems in 2026: Microsoft addressed a mail-flow outage in June that affected customers across several regions. Separate incidents in April caused mailbox access problems across Outlook clients and Exchange connection methods.
Go Deeper -> Microsoft Exchange Online outage causes email failures, auth issues – Bleeping Computer
