Microsoft 365 Outage Disrupts Outlook and Teams Calendar Access Globally

A Microsoft 365 service disruption that began Thursday continued into Friday, with users reporting problems accessing Outlook email and some Microsoft Teams functions. Microsoft said in an update posted at 7:25 a.m. UTC that a patch improved stability on some servers and that the company was working to roll out the fix more broadly, but it did not provide a clear timeline for full restoration.

The incident primarily affected Exchange Online, the cloud service behind Microsoft’s business email and calendars. According to Microsoft, a component that manages secure connections became overloaded, leading affected servers to stop processing certain requests. The company also said it saw no signs of a security breach.

Key takeaways

• Exchange Online—used for Microsoft 365 email and calendar access—was disrupted after a secure-connection handling process became overloaded.
• Microsoft reported partial improvements after a patch, but did not state when service would return to full normal.
• Microsoft 365-linked productivity features were impacted, including elements of Copilot, Defender for Office 365, and some Teams scheduling workflows.
• Third-party systems that rely on Microsoft 365 connectors saw errors, including ChatGPT and Claude email/calendar operations.
• Government and institutional email operations were also affected in multiple countries, underscoring Microsoft 365’s broad dependency footprint.

What Microsoft says caused the disruption

Microsoft’s explanation centered on a bottleneck in how secure connections are handled for affected services. The process that manages these connections was overwhelmed during the incident, causing the servers involved to stop handling requests for some users. The practical result was restricted access to Exchange Online mailboxes, which in turn affected email delivery and retrieval.

In an attempt to mitigate the outage, Microsoft said it restarted parts of its infrastructure, redirected network traffic, and expanded server capacity. By Friday morning, Microsoft indicated that a patch had already improved stability on some servers, but it remained in the process of deploying the update more widely. The University of Pennsylvania’s repost of Microsoft’s incident update did not include any specific restoration timetable.

Ripple effects across Teams, Copilot, and security tools

The outage was not limited to email. Microsoft reported that certain functions tied to Microsoft 365 were also affected, including features in Microsoft Copilot and Defender for Office 365. In Teams, users faced trouble scheduling meetings and sending invitations, though Microsoft stated that most Teams calls and chats continued to work.

For organizations, this distinction matters operationally: calendar and scheduling workflows often depend on timely access to mailbox data and related services. When Exchange Online is degraded, Teams meeting logistics can stall even if real-time communication remains functional.

Why the incident also affected AI and third-party connectors

Because many applications connect to Microsoft 365 using the same underlying account and data access pathways, the disruption also surfaced in AI and productivity integrations. OpenAI reported errors in ChatGPT’s Microsoft 365 connector during the outage. Similarly, Anthropic said the disruption caused most email, calendar, and search requests through the Claude Microsoft 365 connector to fail.

These connector failures highlight a key dependency pattern: even when the core AI service itself is online, application-level features that require accessing Microsoft 365 data can break when Exchange Online or authentication-related components are impaired. For users who rely on these integrations for work—such as summarizing emails or searching calendar information—the outage can immediately reduce those workflows to partial or unusable states.

Real-world impact on courts and government email systems

Multiple institutions reported email connectivity issues. The U.S. Court of Appeals for the Tenth Circuit said its clerk’s office could not send or receive email for much of Thursday. Japan’s Finance Ministry reported it was unable to receive email on Friday, and Singapore’s Government Technology Agency told CNA that government email systems were among those affected.

These reports reflect how Microsoft 365 has become embedded in official communications and administrative operations. When the same underlying cloud email service is disrupted, it can create delays across agencies that depend on timely inbound and outbound messaging.

As Microsoft continues rolling out the fix, the next thing readers should watch is whether Microsoft 365 restores consistency across all affected components—particularly Exchange Online mailbox access—and whether the downstream connectors and Teams scheduling features return to normal. Until Microsoft provides clearer restoration benchmarks, some disruptions may linger even after partial improvements are reported.