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 certain Windows Server updates released in October 2026 may be destabilizing Exchange Server. The problems are related to default memory limits on Endpoint Mapper, affecting Exchange Servers running Windows Server 2016, 2019, 2022, and 2025. The issue may not be immediate and could cause problems with OWA (Outlook Web Access) leading to connection glitches or email queues queuing up for lengthy periods.
Rebooting the server might provide a temporary fix, but a more permanent solution is a registry edit to increase the maximum memory limit. Microsoft strongly advised customers not to uninstall the updates, as the severity and speed of impact vary based on the Exchange server load. Some servers might not experience any issues at all.
While Microsoft is investigating the issue, they have not yet committed to issuing an out-of-band update to resolve the problem.
Written by urgent.news from The Register Software's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
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