why are we not warned not to save .pst files in One Drive?

Question

why are we not warned not to save .pst files in One Drive? It has totally messed up Outlook.

Answer 1

@Susan P. McNeill said

why are we not warned not to save .pst files in One Drive?

Because it worked OK until the Jan 2026 KB5074109 Windows Update. Microsoft did not intend KB5074109 to break Outlook and they are working to modify the update so it no longer causes this problem.

https://support.microsoft.com/en-us/office/classic-outlook-pop-account-profiles-hang-and-freeze-after-windows-11-update-to-kb5074109-590fe356-ecc2-49f4-b9e3-bd39fafa58f6

There are two temporary fixes. Doing either one should fix the issue:

1 -- Move any PST files out of your OneDrive folder and use ScanPST to check for errors.

To see the locations of your PST files:
From the Outlook menu do File > Account Settings > Account Settings. Select the "Data Files" tab.
If your Outlook is not useable - Open the Windows Control Panel. Click on the "Mail" link. On the "Mail Setup" dialog click "Data Files ..."

How to remove an Outlook .pst data file from OneDrive

https://support.microsoft.com/en-us/office/how-to-remove-an-outlook-pst-data-file-from-onedrive-b6b9e522-59bd-40f7-949f-168d0aa9b38e

ScanPST

https://learn.microsoft.com/en-us/troubleshoot/outlook/data-files/how-to-repair-personal-folder-file

2 -- Uninstall the Jan 2026 Update KB5074109 and Pause Windows Updates.

How to uninstall a Windows Update

https://support.microsoft.com/en-us/windows/how-to-uninstall-a-windows-update-c77b8f9b-e4dc-4e9f-a803-fdec12e59fb0

If you can not uninstall KB5074109 thru normal means, see this Microsoft Learn Q&A thread for alternatives.

https://learn.microsoft.com/answers/questions/5707915/outlook-classic-not-opening-properly-or-recording

Or contact Microsoft Support and ask "How to uninstall KB5074109?"

https://support.microsoft.com

Pause Windows Updates

https://support.microsoft.com/en-us/windows/pause-updates-in-windows-643e9ea7-3cf6-7da6-a25c-95d4f7f099fe

Answer 2

2026-01-25 - A fix for the KB5074109 Outlook/OneDrive bug has been released as KB5078127.

https://support.microsoft.com/en-us/topic/january-24-2026-kb5078127-os-builds-26200-7628-and-26100-7628-out-of-band-cf5777f6-bb4e-4adb-b9cd-2b64df577491

Answer 3

Thank you both again. My version of Outlook (W10) is finally working as it should and I have finally been able to open it and delete emails from it. I am still looking into placing the .pst files outside of the reach of OneDrive, however.

I was able to get the appropriate version of patch for Windows 10 - KB5078129 from here: (2026-01 Cumulative Update for Windows 10 Version 22H2 for x64-based Systems (KB5078129).

Answer 4

The fix hasn't shown up on my update dashboard yet, so I tried but the version for W11. It did not even open/work. Information I found indicated that the patch should be compatible with Windows 10 and I as have the security extension for a year, I thought it would work. I will wait a day or so to see if the W10 version shows in updates and do the other things suggested if it doesn't. Thanks again so much. SM

I found the download for the patch here: https://www.catalog.update.microsoft.com/DownloadDialog.aspx

Answer 5

Hello Susan P. McNeill,

Thank you for raising your concern in the Microsoft Q&A forum. I understand your frustration that saving an Outlook Data File (.pst) in OneDrive has caused issues with Outlook. 

The incompatibility arises from a fundamental conflict: Outlook requires continuous, exclusive access to its data files, while OneDrive actively synchronizes files in its folder. When both processes interact with the same .pst file simultaneously, it frequently results in corruption and performance incidents.  

To resolve the current impact on your Outlook, you need to relocate the .pst file to a local directory on your computer that is not synchronized by any cloud service. Please follow these steps in sequence. 

Disclaimer: Before proceeding, please ensure you have backed up your important data to an external drive or another secure location. The following steps involve modifying critical Outlook data files. 

1, Close Outlook and Pause OneDrive. 

• Exit Outlook completely. 
• Right-click the OneDrive icon in your system notification area and select Pause syncing > 2 hours or choose Quit OneDrive. 

2, Locate and Copy the .pst File. 

• Press the Windows key + R, type %localappdata%\Microsoft\Outlook, and press Enter. 
• Identify your Outlook Data File (files with the .pst extension). 
• Copy this file (Ctrl+C). Do not move or delete the original at this stage. 
• Create a new folder on your local hard drive, for example, C:\OutlookData. 
• Paste the copied .pst file into this new local folder. 

3, Reconfigure Outlook to Use the New File Location. 

• Launch Outlook. If an error appears stating the data file cannot be found, select OK. 
• Navigate to File > Account Settings > Account Settings. 
• Select the Data Files tab. 
• Choose the data file entry that references the old OneDrive path and click Remove. (This action removes the file from Outlook's profile but does not delete it from your disk.) 
• Click Add..., browse to and select the .pst file from its new local location (e.g., C:\OutlookData), then click OK. 
• Close the Account Settings windows. 

4, Verify and Clean Up. 

• Restart Outlook. Your email folders and data should now be accessible from the new location. 
• After confirming Outlook is functioning correctly, you may safely delete the original .pst file from your OneDrive folder to prevent future synchronization conflicts. 

5, Repair the Data File. 

If Outlook continues to experience instability, the data file may require repair. 

• Close Outlook. 
• Press Windows key + R, type scanpst.exe, and press Enter to open the Inbox Repair Tool. 
• Click Browse, navigate to and select your .pst file from its new local location, then click Start. 

If the issue persists, to assist with further investigation, could you please describe the specific symptoms you are encountering? For instance, is Outlook failing to start, displaying error messages, or are emails missing? 

Please attempt the provided steps and inform me of the outcome. I look forward to your update for further analysis. 

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