OneDrive File Issues

How to Fix OneDrive Sync Problems with Outlook PST Files

Elise Williams Sep 28, 2026 868 views

Question details

Users experience recurring sync failures and file conflicts when attempting to synchronize an Outlook PST file using the OneDrive client.

Fixing OneDrive Synchronization Problems with Outlook PST Files

Product: Microsoft Outlook and OneDrive
Device & OS: not provided
Scenario: Synchronizing or backing up local email data files to cloud storage.
Observed behavior: OneDrive displays sync errors or creates duplicate conflict files because the active PST file is locked by the Outlook application.

Before you start

Verify that Microsoft Outlook is completely shut down and no background Outlook processes are running in the Task Manager, as active PST files cannot be accessed or moved by external applications.

Solution 1Recommended

Exclude the Active PST File and Manually Backup to OneDrive

Move your active PST file outside the OneDrive sync folder to stop continuous errors, and manually copy it to OneDrive only when Outlook is closed.

Microsoft actively discourages syncing connected PST files through the OneDrive sync client. Because Outlook requires exclusive read/write access to the database file, it locks the file while the program is open. This constant locking prevents OneDrive from uploading the file, resulting in sync failures.

Close Outlook and locate your PST file

Exit Microsoft Outlook completely. Open File Explorer and navigate to your current PST location (commonly C:\Users\[Username]\Documents\Outlook Files).

Move the PST file out of OneDrive

If your Documents folder is automatically synced by OneDrive, move the PST file to a local folder that is not synced, such as C:\LocalOutlookData.

Reconnect the PST file in Outlook

Open Outlook. It will prompt you that the data file is missing. Browse to the new location (C:\LocalOutlookData) and select your PST file to reconnect it.

Manually copy the file for backup

Whenever you need to back up your email data, close Outlook completely, copy the PST file, and paste it into your OneDrive for Business folder to upload it safely.

Exclude the Active PST File and Manually Backup to OneDrive

Best Practice: Manually copying the file ensures that you have a point-in-time backup without causing file locks or database corruption in your daily email workflow.

Solution 2

Use a Dedicated Backup Solution

Utilize professional backup software that is designed to handle locked database files and can back up to external drives or cloud targets.

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Frequently Asked Questions

Why does Outlook lock the PST file?

Outlook requires exclusive read and write access to the PST file to manage incoming and outgoing emails efficiently. This strict locking mechanism prevents other programs from modifying the file simultaneously, which could lead to severe database corruption and data loss.

Can I use OneDrive to synchronize Outlook OST files?

No. OST files are offline cache files linked to Exchange or IMAP accounts. Microsoft explicitly states that OST files should not be synced via OneDrive. If an OST file is lost, Outlook simply rebuilds it by downloading the emails from the server again.

Where are my Outlook PST files typically located on Windows?

By default, Outlook 2013 and later versions save PST files in the 'Documents\Outlook Files' folder. In older versions, they may be hidden in 'C:\Users\[YourUsername]\AppData\Local\Microsoft\Outlook'.

How do I stop OneDrive from automatically syncing my Documents folder?

Click the OneDrive cloud icon in your system tray, select Settings (gear icon), go to the 'Sync and backup' tab, click 'Manage backup', and toggle off the Documents folder. Note that this will stop syncing all files within that folder, so moving the PST file to a non-synced directory is usually preferred.

Document & File Issues