Microsoft has acknowledged that the October 2026 Windows Server updates may be destabilizing Exchange Server. The problems are related to this list of Windows Server updates (see here) and Microsoft makes it clear they are not related to the October 2026 security updates for Exchange Server. The software giant says the bug can hit Exchange Servers running Windows Server 2016, 2019, 2022, and 2025. The glitch might not be immediate and could impact Exchange Server OWA, which can throw up connection glitches or cause lengthy email queues, "with email crawling to a halt." Rebooting the server might make the problem go away temporarily, but a more permanent workaround is a registry edit. The destabilization issue could impact Exchange Server 2016, 2019, and the new Subscription Edition (SE), says the Windows maker. Microsoft strongly advised that customers should not uninstall the October 2026 Windows Server update and stated, "Not all Exchange servers will be impacted by installation of those updates equally; the severity and speed of impact varies based on Exchange server load. Some servers might never see a problem." However, for those administrators who found their weekend swallowed by borked Exchange Servers, the registry edit is currently the only workaround. The cause of the issue is a default limit on the amount of memory used by Endpoint Mapper when handling Endpoint Lookup calls…