Microsoft’s Exchange Online service suffered a significant outage on August 31 that disrupted email delivery and sign-in for users across the globe. The company acknowledged the incident — tracked internally as EX1464935 and later MO1465074 — after tens of thousands of users reported via Downdetector and social media that they could not send or receive email, search their mailboxes, or sign in to Microsoft 365 services. Symptoms included delayed and failed email messages, broken search results, authentication errors when accessing Exchange Online, and difficulties using the Exchange administration console.
The outage quickly spread beyond email alone. Microsoft confirmed that OneDrive for Business, SharePoint Online, Microsoft Teams, Microsoft Purview, and Microsoft Defender XDR were all affected. Engineers traced the problem to a core authentication configuration used by multiple internal services within the Exchange Online infrastructure and began manually resetting individual servers to restore service. The company said it was still assessing the full scope of impact as of its last published update. Microsoft has dealt with several Exchange Online outages in recent months, including a widespread mail-flow disruption in June affecting North America, Asia-Pacific, and Europe, and intermittent mailbox access problems in April.
How to check if you’re affected
Affected versions include all Microsoft 365 plans that include Exchange Online — consumer Outlook.com accounts are separate and were not reported as part of this incident. If you use a work or school email account hosted on Microsoft 365, check your organization’s Microsoft 365 admin center (look under Service Health) or the public Microsoft 365 Status page for the current state of the EX1464935/MO1465074 incident. If email is flowing normally, the outage has been resolved for your tenant.