Microsoft 365 Outage Enters Second Day As Outlook Mail Recovers, Teams And Copilot Issues Persist

Microsoft is continuing to restore Microsoft 365 services after an authentication-related outage disrupted Exchange Online and Outlook, while also affecting Microsoft Teams, Microsoft 365 Copilot, OneDrive, SharePoint, and other enterprise services.

The disruption began on August 31 and carried into September 1, with Microsoft reporting improving service availability but continuing to monitor affected infrastructure and residual problems.

TL;DR

 

• Microsoft linked the outage to a core authentication configuration used across multiple Microsoft 365 services.
• Outlook and Exchange Online users faced email delivery, login, connectivity, and search problems.
• Teams, Copilot, OneDrive, SharePoint, Purview, Defender XDR, and other services were also affected.
• Microsoft says much of its remediation has been deployed, but the incident remains under monitoring.

Microsoft Outlook And Exchange Online Users Face Second Day Of Problems

What initially appeared to be a Microsoft Outlook outage turned out to be a wider Microsoft 365 service disruption affecting several enterprise applications.

Source

CNET reported that more than 6,000 Outlook problem reports were recorded on Downdetector at around 8:17 a.m. PT on August 31. At that snapshot, 37% of reports concerned receiving messages, while users also reported problems with the Outlook app and website.

By September 1, Sunday Guardian Live reported another rise in complaints from US users. Its Downdetector snapshot showed receiving-message problems accounting for 39% of reports, login problems at 24%, and app-related problems at 22%. These percentages represent categories among reports submitted to Downdetector, not the percentage of Microsoft's overall customer base affected.

Microsoft tracks the Exchange Online disruption under incident EX1464935.

According to Microsoft's service-health information reproduced through the University of Pennsylvania's PennO365 incident feed, affected users could experience delays or failures when sending and receiving emails, incomplete search results, authentication errors, administration problems, and intermittent mailbox failures.

What Caused The Microsoft 365 Outage?

Microsoft attributed the problem to an issue involving a core authentication configuration used by multiple Microsoft 365 services.

The company subsequently expanded the incident under reference MO1465074 after confirming that the authentication problem extended beyond Exchange Online. Microsoft began reapplying authentication components and restarting affected sections of its infrastructure as part of the remediation.

Bleeping Computer independently reported that Microsoft first focused on Exchange Online before confirming the wider impact across its Microsoft 365 portfolio, including Teams, OneDrive, SharePoint, Purview, and Defender XDR.

Computerworld also reported that Microsoft had restored much of Exchange Online's mail flow while continuing to work on search and other affected functionality as the incident entered its second day.

Microsoft Teams, Copilot, OneDrive And Other Services Were Affected

Microsoft's incident data shows that the problem extended across a much wider group of productivity and enterprise services.

Microsoft 365 Copilot prompts that required Microsoft 365 data, such as information from emails, could fail. OneDrive for Business and SharePoint Online users could encounter problems loading content, searching for files, opening documents, synchronizing OneDrive, or viewing recent and shared content.

Microsoft Teams users could experience problems with calendars and search, while presence information could become outdated. Some Teams Rooms devices and desktop phones could also appear offline in the Teams Admin Center.

Microsoft also listed intermittent authorization failures affecting Purview and Defender XDR, authentication problems in the Microsoft 365 Admin Center, and failures involving Universal Print among the possible effects of the broader incident.

What Did Microsoft Say About The Outage?

Microsoft said service telemetry was showing increasing availability as its fix progressed.

In its latest detailed update available during our review, the company said, “A substantial portion of the remediation deployment has been completed,” adding that remaining organizations should recover as the fix reaches their infrastructure.

Microsoft also acknowledged the impact on customers and said that “resolving it remains our highest priority.”

A Microsoft spokesperson separately told Tom's Guide, “We know this is disruptive for customers,” while directing users to Microsoft's service health page and its Microsoft 365 Status account for updates.

Is Microsoft 365 Still Down?

Microsoft's latest incident records available during our September 1 review continued to classify both the broader Microsoft 365 incident and the Exchange Online incident as service degradations rather than fully resolved events.

 

However, Microsoft reported that a substantial amount of the remediation had already been deployed and that service telemetry was showing continued recovery. Exchange Online mail flow had recovered significantly, while Microsoft continued validating authentication, connectivity, search, and other affected workflows for residual problems.

This means users may see services return at different times depending on the Microsoft infrastructure serving their organization, rather than experiencing one simultaneous restoration across every Microsoft 365 product.