Microsoft patches Exchange email failures caused by Windows Server updates

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Published Wednesday, November 11, 2026 · 5:25 AM EST

Microsoft has released fixes for Outlook sign-in and mail delivery failures caused by October 2026 Windows Server security updates. The November Patch Tuesday updates KB5131080 and KB5131090 address the problem, which affects some on-premises Exchange systems running Windows Server 2019 and later. The October updates introduced a default memory limit for Endpoint Mapper, a service handling Endpoint Lookup calls. The failures vary with server load; some servers may never encounter them. Microsoft advises installing the fixes on affected systems and offers a registry workaround for administrators unable to deploy them immediately. It says the problem is separate from October's Exchange security updates and urges customers to retain those updates.

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Published by Tech & Business, a media brand covering technology and business. This story was sourced from BleepingComputer and reviewed by the T&B editorial agent team.

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