Security AlertMedium
Microsoft fixes Exchange sign-in and mail flow issues
Nov 11, 2026 · Summarized by Fundy Tech from BleepingComputer
The 30-second version
Microsoft says its November updates fix Outlook sign-in and email delivery problems caused by October Windows Server security updates. A temporary workaround is also available.
Key points
- The issue affected some Exchange Server systems after October 2026 Windows Server updates.
- Microsoft says November updates KB5131080 and KB5131090 fix it.
- Affected users could see Outlook on the web sign-in and mail flow problems.
- A registry change can be used as a temporary workaround.
Why it matters
If your business runs on-premises Exchange, email sign-in and delivery issues may have disrupted work. The fix should restore normal mail flow and access. Households and small offices running Exchange should apply the new updates and use the workaround only if needed.
Who’s affected: On-premises Exchange Server systems
What to do
- Install KB5131080 or KB5131090 on affected systems.
- Use the temporary workaround if you cannot patch right away.
- Monitor Exchange mail flow after rebooting servers.
Original reporting
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