Microsoft 365 Outage Disrupts Outlook, Exchange Online and Teams - SecurityWeek

Microsoft initially reported issues with Exchange Online mailboxes in the Americas before identifying potential disruption to Teams, SharePoint Online, Microsoft 365 Copilot and Defender XDR. Some Google Workspace users also reported trouble accessing their Google-hosted email through Outlook clients.

The company traced the problems to a large number of servers becoming unavailable, with remaining systems handling the increased load. Microsoft stated that overall traffic had not increased, and affected servers were failing automated health checks.

Investigation continues

Microsoft is investigating what triggered the failures and has found no evidence of a cyberattack. The company has not explained why health checks failed or why processor usage rose on affected servers. The disruption occurred two days after Microsoft released November Patch Tuesday updates addressing 1,094 vulnerabilities, including an Outlook spoofing flaw (CVE-2026-124194) that attackers have exploited.

Microsoft's service advisories have not linked the vulnerability to the Exchange Online outage.

Status update

Microsoft is tracking the Exchange Online disruption under EX1550543 and the broader Microsoft 365 incident under MO1550821. As of just before 3 p.m. ET, both incidents were listed as service degradations. The company is testing a workaround that bypasses the component responsible for processing health checks while continuing to investigate the root cause.