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Impacted by October 2026 Windows Server Updates Causing Exchange OWA Failure.
If the October 2026 Windows Server updates are causing Exchange Outlook on the web (OWA) failures, the safest approach is to confirm the affected update and Exchange version before uninstalling anything.
Check Microsoft’s Exchange Server Health Checker and release notes for known issues.
Review IIS, Exchange, and Windows event logs to identify the failure.
If production email access is affected, follow Microsoft’s documented mitigation or recovery guidance for your specific Exchange version.
Avoid rolling back security updates without assessing the risk.
Microsoft has confirmed this issue as of October 15, 2026. The October Windows Server updates may cause Exchange OWA failures and growing email queues.
Affected updates include:
Windows Server 2025: KB5126646
Windows Server 2022: KB5126655
Windows Server 2019: KB5126651
Windows Server 2016: KB5126868
Recommended action: Check Microsoft's
official Exchange update advisory . Microsoft is investigating and has not yet confirmed a workaround. Avoid uninstalling security updates without a recovery plan.
Is it expected Microsoft widows team publish a hot-fix update soon in resolving this issue?
As the impacted deployment version is Windows server 2016, and Exchange server 2016 with 2 nodes DAG and hybrid cloud 365 deployment.
The issue indicates after we installing the CU update for windows server 2016.
Since, We are rebooting the Exchange server one time per day to solve the stuck OWA, Active sync mobile access, mail flow as well.