Admin: 'I spent all weekend on my servers' after Microsoft breaks Exchange Server with October updates
OWA borked and lengthy email queues reported on busy servers after Microsoft tweaks a Server default
Microsoft has acknowledged that October 2026 Windows Server updates may be destabilizing Exchange Server. The issues are related to specific Windows Server updates, but not the security updates for Exchange Server. The bug can affect Exchange Servers running Windows Server 2016, 2019, 2022, and 2025. Symptoms include connection glitches, lengthy email queues, and a crawling email system.
Rebooting the server might provide a temporary fix, but a more permanent solution involves a registry edit. Microsoft advises against uninstalling the updates, as the severity and speed of impact vary based on server load. Some servers might not experience any problems. The root cause is a default limit on memory used by Endpoint Mapper during Endpoint Lookup calls.
Microsoft is investigating the issue and has provided a registry workaround in the meantime. Some customers have expressed frustration, arguing that the updates should have been tested properly before release.
Written by urgent.news from The Register Science's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
