NewsPublished 12 Nov 2026

Microsoft 365 Outage Disrupts Outlook, Exchange Online and Teams

Source SecurityWeek

Description

Microsoft 365 experienced a widespread outage affecting Outlook, Exchange Online, Teams, and other services due to failed server health checks. Microsoft has not found any evidence of a cyberattack and is still investigating the root cause. The outage caused service degradation but was not linked to recent patched vulnerabilities. The company is testing workarounds to restore service.

Impact

The outage disrupted access to key Microsoft 365 services including business email and collaboration tools across multiple regions, causing service degradation. Users experienced connectivity issues with Exchange Online mailboxes and other services. The incident did not involve confirmed exploitation or compromise, and no evidence of cyberattack was found. The disruption affected productivity but did not result in data breaches or security incidents as per current information.

Defensive guidance

Microsoft is actively investigating the root cause and testing a workaround to bypass the failing health check component. There is no indication that customer action is required at this time. Administrators should monitor the Microsoft 365 admin center for updates under incident IDs EX1550543 and MO1550821. No specific security mitigations are necessary since no malicious activity has been detected.

References

securityweek.com/microsoft-365-outage-disrupts-outlook-exchange-online-and-teams/ (opens in a new tab)

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AI analysisMachine-generated, updated 12 Nov 2026, 21:03 UTC

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