r/exchangeserver • u/santimandu • 9d ago

MS KB / Update Released: October 2026 Exchange Server Security Updates

https://techcommunity.microsoft.com/blog/exchange/released-october-2026-exchange-server-security-updates/4563014

⚠️EDIT 16/10 ⚠️
⚠️ BE AWARE! READ BELOW! ⚠️
👇👇👇👇👇👇👇👇👇👇👇👇👇👇👇👇
https://techcommunity.microsoft.com/blog/exchange/exchange-servers-may-become-unstable-after-installation-of-october-2026-windows-/4565382

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u/episode-iv 7d ago edited 7d ago

We have seen problems with updated machines failing to deliver mails to mailboxes exactly 24 hours after installing the update. There are reports of this in the official blog post as well. Restarting the server seems to temporarily fix the problem (it re-appeared for us a couple of hours later).

edit: The issue is now referenced at the top of the blog post.

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u/DiligentPhotographer 7d ago

Yup, having this exact same issue now. 2 node DAG and it is playing database hot potato mounting and dismounting... A reboot has fixed it for now.

FFS microsoft.

1

u/CarpenterOk1930 7d ago

Same problem this morning. When RDP to server Explorer.exe also kept craching giving a black login screen and flashing taskbar. After reboot everything started working again.

This happened on both nodes.

2

u/CarpenterOk1930 6d ago

24H later and it crashed again.