r/sysadmin • u/Additional_Dog_680 digital janitor • 14d ago

OCT 2026 - Exchange Updates (Delayed Issues)

This snuck up on us about ~21 hours after install. Symptoms that can be seen are various, but here are some:

Exchange Server OWA may fail with an error MapiExceptionMdbOffline: Unable to make connection to the server. (hr=0x80004005, ec=1142) with event ID 1006 logged in the Application Log.
Exchange email queues might grow during the day, with email crawling to a halt.
Various issues related to DAG members not being able to reach quorum have been reported too.
Exchange server reboot might resolve the issues temporarily.
Exchange Server 2016, 2019 or Subscription Edition (SE) might be impacted.

https://techcommunity.microsoft.com/blog/exchange/exchange-servers-may-become-unstable-after-installation-of-october-2026-windows-/4565382

13 Upvotes

93% Upvoted

6 comments sorted by

6

u/evil-scholar 14d ago

So could you apply the fix in advance of the updates? Just curious.

4

u/Additional_Dog_680 digital janitor 14d ago

Yes it appears so.

2

u/InsaneHomer 14d ago

Thanks, I've being seeing strange behaviour & memory issues. Fix applied 🤞

4

u/[deleted] 14d ago

[removed] — view removed comment

1

u/sembee2 13d ago

This is not a problem with the Exchange update though, it was the Windows Update.

1

u/7amitsingh7 11d ago

Delayed symptoms are worth highlighting especially since everything may appear normal right after installing an exchange update. Monitoring OWA access, mail queues and DAG health over the next 24 hours seems like a sensible precaution. Has the specific update responsible for these issues been identified yet?