OneDrive: Sync Delay - You may be experiencing a temporary sync delay due to high service activity

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OneDrive: Sync Delay - You may be experiencing a temporary sync delay due to high service activity

Clint Dias 20

I received this sync error: OneDrive: Sync Delay - You may be experiencing a temporary sync delay due to high service activity; On my outlook pst file, it is 526,521kb. I have reset One drive and it uploaded the file but the next time there was a change to the file size I receive the same error. Is there a way to overcome this?

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Answer 1

Chloe-L 8,540 Microsoft External Staff Moderator

Dear Clint Dias,

Thank you for posting to the Microsoft Q&A and describing these symptoms so clearly.

I understand how disruptive it is when Outlook stops responding and your inbox becomes cluttered with previously deleted emails. The behavior you described—where Outlook "forgets" what you have read or deleted—is likely related to a known issue in the recent Windows Update (KB5074109).

User's image

This update can cause Outlook to get stuck running in the background even after you close it, which corrupts the local database (OST) and causes it to lose track of your email history. You can track the official status of the fix in this support article: Classic Outlook POP account profiles hang and freeze after Windows 11 update to KB5074109

In the meantime, the best way to restore your workflow is to temporarily remove this specific update. Here are the steps to do that:

Open Windows Settings
Go to Windows Update > Update History.
Scroll down to the "Related settings" section and click Uninstall updates.
Locate Security Update for Microsoft Windows (KB5074109) in the list.
Click Uninstall next to it.
Restart your computer.

Tip: To prevent Windows from automatically reinstalling this update tonight, go to Settings > Windows Update and click "Pause updates for 1 week." This will keep your system stable until the official permanent fix is released.

I hope rolling back this specific update restores your Outlook stability while the engineering team prepares the permanent patch. I will follow up with you here as soon as the permanent fix is released so you can safely update again.

Thank you for your patience and understanding while Microsoft is working on the solution.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

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Clint Dias 20 Reputation points

2026-01-19T07:38:34.1633333+00:00

Hi Chloe, thank you for your detailed response it is appreciated. I uninstalled the security update, restarted my machine and the same error came up. I then quit one drive and started it again and the same error came up. I then reset one drive and the error disappeared and the file uploaded. I restarted my machine and the error came up again. could it be something else?
Chloe-L 8,540 Reputation points Microsoft External Staff Moderator

2026-01-21T15:52:45.19+00:00
Dear Clint Dias,

Thank you so much for the update and for your patience in trying those initial steps.

Please follow these steps to safely move your Outlook data file out of the OneDrive syncing folder.

Close Outlook and wait for OneDrive sync to complete.

Open File Explorer and browse to C:\Users\[username]\OneDrive\Documents\Outlook Files.

Copy the .pst file from the OneDrive folder to a new or existing location on your PC which is not in your OneDrive (e.g. C:\My Outlook Files).

Give the copied file a new name (e.g. ******@domain-copy.pst).

Restart Outlook.

Select File then Account Settings:

In the Email tab, choose the account name and then select Change Folder:

Choose the account and select New Outlook Data file:

Browse to the location of your newly renamed copy .pst file, select it, and choose OK to return to the Email Accounts list.

On the Data Files tab, choose the data file location which includes OneDrive and select Remove and Yes to disconnect the file.

Note:

Default File: If the "Remove" button is greyed out, it means that file is set as the "Default." You must select your new file and click Set as Default first. Then you can remove the old one.

Cleanup: Once you are sure everything is working perfectly with the new file, you can manually delete the old .pst file from your OneDrive folder to stop the sync errors permanently (make sure Outlook is closed when you do this).

I know this involves a few extra steps but moving that database file to a quiet local folder is the best way to ensure stability. Please let me know if you run into any roadblocks during the move.
Clint Dias 20 Reputation points

2026-01-22T06:32:39.34+00:00

Hi Chloe, thank you for your assistance it is valued and appreciated. Perhaps I need to elaborate a bit. The PST files Outlook looks at is in my user folder and not linked to one Drive at all. I have three pst files with different addresses for three different email accounts. I have installed a program called free file sync and then set up a task in windows task scheduler that when I log in Free file sync runs a batch file and syncs my Outlook pst files from my user folder to my desktop folder. One drive then syncs the files in the desktop folder. The other two smaller pst files sync without a problem, its just the larger file that gives the error. The reason I set it up this way was that when one drive synced the pst files outlook was using Outlook failed to operate correctly, it only operates correctly when the files are separate from one drive.
Chloe-L 8,540 Reputation points Microsoft External Staff Moderator

2026-01-24T23:09:48.5866667+00:00
Dear Clint Dias,

Thank you very much for providing that clarification. Understanding that you are using FreeFileSync and Task Scheduler to create a bridge between your active folder and the OneDrive-synced Desktop folder helps me a lot.

The technical behavior you are experiencing is due to the fundamental difference between how OneDrive handles standard files versus complex database structures like a .pst file.

In contrast to a standard Word document—where OneDrive can efficiently sync only the specific sentences you changed—a .pst is a complex database. When even a single email is received or moved, the internal structure of that entire ~526MB file is altered.

Because the file is large and changing frequently (triggered every time your task scheduler runs the sync), OneDrive’s sync engine perceives this as a sustained, high-bandwidth demand. To protect your system resources and prevent the upload tunnel from being overwhelmed, the engine essentially "throttles" the sync and triggers the "High service activity" error.

Recommended Solutions:

To ensure your backup remains stable without triggering these service errors, I suggest the following adjustments to your workflow:

Zip & Sync: OneDrive handles compressed archives much more efficiently than raw database files. You could modify your FreeFileSync batch script or use a simple PowerShell command to compress the .pst into a .zip file within your OneDrive folder. This reduces the file size and presents a "static" archive to OneDrive, which is much easier for the service to process.

Increase the Sync Interval: If your Task Scheduler is currently set to sync "On Logon" or at frequent hourly intervals, the frequency itself may be the trigger for the throttle. I recommend changing the schedule to once a day (perhaps at the end of your workday) to allow OneDrive to complete the large upload without constant interruptions.

Utilize an Alternative Backup Method: Technically, Microsoft does not recommend using active sync engines for live-synced .pst files. If you require OneDrive for backup purposes, it is best to upload a "closed" copy of the file. Alternatively, you might consider syncing that specific file to an external drive or using a dedicated backup service (like Azure Backup) that is designed for large database transfers rather than real-time synchronization.

I hope my explanation and the recommendations provided work effectively for your workflow. If you have any other questions or encounter further technical snags, please don't hesitate to reach out.
Clint Dias 20 Reputation points

2026-01-26T05:46:11.6866667+00:00

Hi Chloe,

Thank you for your explanation and assistance it is very helpful and appreciated. I will certainly try ZIP the file, failing which I will backup manually.
Gabe Bratton 601 Reputation points Microsoft Employee Moderator

2026-01-26T17:16:38.7433333+00:00

The Windows fix is now available as update KB5078127. See this article for more information, https://support.microsoft.com/en-us/office/classic-outlook-profiles-with-pop-accounts-and-psts-hang-after-windows-updates-on-january-13-2026-590fe356-ecc2-49f4-b9e3-bd39fafa58f6.
Chloe-L 8,540 Reputation points Microsoft External Staff Moderator

2026-01-28T00:31:04.4766667+00:00

Dear Clint Dias,

You are very welcome! That sounds like a solid plan.

Please let me know how you get on or if you encounter any other hurdles. I’m happy to help further.

If you find that the method successfully stabilizes your backup routine, please feel free to mark the response as the "Answer." This is very helpful for other community members who might be managing similar PST setups, as it allows them to find this verified workflow quickly.

Best regards,

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OneDrive: Sync Delay - You may be experiencing a temporary sync delay due to high service activity

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