how to get KB5078127 fix

Question

My Outlook is freezing shortly after opening. I'm using Classic Outlook with PST file on OneDrive. After I get a "Not responding" msg, I select close program. But can't restart Outlook, just a momentary pop-up banner then nothing. I do see an icon on Hidden icons (Task Bar that just says "Outlook is closing") and Outlook.exe still present on Task Manger under Background Processors. If I kill this process or restart Windows, this problem clears until I open Outlook again. I can access my email via Remote Email fine.

I see KB5078127 fix exists but is not listed on my Update History. How do I get this update, and will this fix my problem?

Thank you.

Answer 1

Yes, KB5074109 was installed and the problems started to happen with Outlook (Classic). I then un-installed KB5074109 and the problems appeared to go away. Now KB5078127 is not offered anywhere for me to install.

Answer 2

Hi,

Thank you for sharing your question. I understand how disruptive it is when Outlook becomes unresponsive shortly after opening, especially when you rely on a PST file stored on OneDrive, which makes restarting the app difficult due to the lingering Outlook process.

The KB5078127 update is an out‑of‑band emergency fix released by Microsoft to address exactly the issue you’re encountering, where classic Outlook becomes unresponsive when PST files are stored in cloud‑synced locations such as OneDrive. Microsoft confirmed that Outlook may hang on launch and fail to reopen unless the process is terminated or Windows is restarted.

To get this update, you can go to Settings > Windows Update > Check for updates, where it should appear automatically if your device received the January 2026 Patch Tuesday updates. If it does not appear, you can download it manually from the Microsoft Update Catalog as Microsoft also distributes the fix through direct download.

This update is specifically designed to fix unresponsive behavior in Outlook Classic involving PST files on OneDrive, so installing it should address your freezing issue.

May I also ask are you using Windows 11 version 24H2 or 25H2, and have you recently installed the January 2026 Patch Tuesday update (KB5074109)? Knowing this will help me confirm whether KB5078127 should already be offered to your device.

Feel free to share your Windows version or results after checking for updates, and I’ll be happy to help you verify installation or explore additional steps if the issue continues.

 

I hope this helps.

 

Best Regards,

Noel

Answer 3

The Microsoft Catalog shows two .msu files and appear different sizes. So not sure if one uses one or both.

Answer 4

I am running Windows 11 25H2 (26200.7623) and I see 2026-01 Security Update (KB5074109) (26200.7623) installed on 1/14/2026. Even after Check for Updates, I see only a Preview Update (KB5074105). Which should i do? Uninstall KB5074109 or locate and install KB5078127. If later I may need more help.

Answer 5

The update is not shown under History, automatic update is on and Download & Install shows only another Preview Update for KB5074105. How can a "Preview" fix my problem?