# Microsoft patches Exchange email failures caused by Windows Server updates

_Published Wednesday, November 11, 2026 at 5:25 AM EST · Infrastructure, Products · Latest · Tier 2 — Notable_

![Microsoft patches Exchange email failures caused by Windows Server updates — Primary](https://www.bleepstatic.com/content/hl-images/2026/10/22/Exchange_Online.jpg)

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.

## Sources

- [BleepingComputer](https://www.bleepingcomputer.com/news/microsoft/microsoft-fixes-exchange-sign-ins-broken-by-october-windows-server-updates/)

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Canonical: https://techandbusiness.org/newswire/RBkXH7alpzaHKqQ9_lD1VJ
Published: 2026-11-11T10:25:51.079Z
Story chronology: 2026-11-11T09:07:27.000Z
Retrieved: 2026-11-11T12:45:32.885Z
Publisher: Tech & Business (techandbusiness.org)