Microsoft 365 services, including Outlook and Teams, are down for thousands of users in the United States as the company investigates problems with Exchange Online. ^[1] Microsoft 365 services, including Outlook, SharePoint, Copilot, Teams, Purview, Defender XDR, the Microsoft 365 Admin Center, and Universal Print, were affected by an outage starting on Sunday, September 1, 2026. ^[2] As of 3:15 p.m. EDT, the services continued to experience problems, with thousands of users still reporting outages across the United States. ^[3] Microsoft stated on X that it identified an issue with an authentication component which is contributing to the impact and is applying a remediation strategy to a portion of infrastructure to test its efficacy. ^[4] Reports of issues with Microsoft Outlook began coming in around 12:15 p.m. EDT on Monday, with thousands of users unable to send or receive emails or log in to Outlook. ^[5] Microsoft stated on September 1, 2026, that mitigation actions were continuing to progress and that indications from telemetry remained positive. ^[6] The outage was caused by a misconfiguration issue with a core authentication configuration used by multiple Microsoft 365 services, which prevented authentication components from deploying as expected to a portion of the infrastructure. ^[7] By 10 p.m. ET on Monday, September 1, 2026, Microsoft reported that mail flow was improving but search functionality remained degraded. ^[8]