Unable to Upload PST Files to OneDrive: 8 Ways to Fix It

PST files often get stuck on the Preparing to upload screen in OneDrive, stall partway through, or fail outright with a sync error. It rarely means the file is broken. Outlook usually still has the file open, a background process is holding a lock on it, or OneDrive is struggling with the fact that a PST is one large database file instead of many small ones. Here is how to identify which of these is happening and fix it.

Why You Can’t Upload PST Files to OneDrive

A PST file is a single database file, so any small change to it means the whole file has to sync again, not just the new part.

• Outlook or a background process (such as Windows Search Indexing) still has the PST file open and locked
• The PST file is too large or exceeds OneDrive’s individual file size limit
• OneDrive sync client is stuck, corrupted, or running an outdated version
• The PST is stored on a mapped network drive or an already-synced cloud location, which OneDrive does not support for live Outlook data files

Fix 1: Close Outlook and Any Background Processes Using the PST

Outlook keeps the PST file locked the entire time it is running, and OneDrive cannot read a locked file to upload it.

• Close Outlook completely, then open Task Manager and check the Details tab for OUTLOOK.EXE still running in the background, and end it if present
• Also check for SearchIndexer.exe, since Windows Search can hold an open handle to the PST while indexing mail content, and pause indexing from Indexing Options if it keeps re-locking the file
• Once nothing else has the file open, check the OneDrive activity center to see if the upload resumes on its own
• If the upload still does not move, the file’s location or the sync client itself is likely the problem rather than a lock, so continue to the next fix

Fix 2: Move the PST Outside the OneDrive Folder

If the PST lives inside a folder OneDrive is actively syncing, or on a mapped network drive, Outlook and OneDrive end up fighting over the same file, and OneDrive cannot reliably sync a file another app keeps modifying.

• Right-click the PST file in File Explorer and check its location under Properties
• If the path is inside the OneDrive folder, or points to a mapped network drive (a lettered drive backed by a server), copy the PST to a local, non-synced folder such as C:\Users\<name>\Documents
• In Outlook, go to File > Account Settings > Account Settings, open the Data Files tab, click Add, and select the relocated PST file
• Remove the old OneDrive-based PST entry once Outlook is confirmed to be using the new one, then upload the relocated copy as a standalone file rather than a live data source

Fix 3: Update or Reset the OneDrive Sync Client

A stuck or outdated sync client can mishandle large single files like PST and stall without showing a clear error.

• Click the OneDrive cloud icon in the taskbar, open Help and Settings, and select About OneDrive to check the version against the latest OneDrive sync client release, and update if it is outdated
• If the client is up to date but still stuck, press Win + R, paste %localappdata%\Microsoft\OneDrive\OneDrive.exe /reset, and press Enter to rebuild the sync database without deleting any files
• Wait a few minutes for OneDrive to restart automatically, sign in again if prompted, and let it finish its initial sync before retrying the PST upload

Fix 4: Compact or Archive the PST Before Uploading

A PST accumulates unused space from deleted items, which inflates the file and slows down or stalls the upload of the entire file on every change. Freezing it into a static copy also stops Outlook from modifying it mid-upload.

• In Outlook, go to File > Account Settings > Account Settings, open the Data Files tab, select the PST file, click Settings, then Compact Now, and let it finish before closing Outlook
• For an extra layer of protection against the file changing mid-upload, right-click the compacted PST, select Send to, then Compressed (zipped) folder, and upload that ZIP copy instead of the raw PST
• Try the upload again once the file size has reduced or the ZIP copy is ready

Fix 5: Pause and Resume OneDrive Sync

Restarting the sync session can clear a stalled upload task without needing a full reset.

• Click the OneDrive cloud icon in the taskbar, then the Help and Settings gear icon
• Select Pause syncing and choose 2 hours, then wait 10 to 15 seconds
• Open the same menu again and select Resume syncing
• Check whether the PST upload progresses past Preparing to upload

Fix 6: Upload the PST Through the OneDrive Website Instead

If the desktop sync client keeps failing regardless of the fixes above, uploading directly through the browser bypasses the sync client and its stuck sessions entirely.

• Close Outlook completely so the file is not in use
• Sign in to the OneDrive website, open the destination folder, and click Upload > Files
• Browse to the PST (or the ZIP copy from Fix 4), select it, and click Open
• Wait for the upload to finish in the browser before reopening Outlook or restarting the OneDrive desktop app

Fix 7: Exclude the PST Folder Instead of Syncing It Live

If none of the fixes above get the upload moving, or it succeeds once but keeps failing on later changes, the real issue is usually that OneDrive is built for files that change in small pieces, not a single large database file that Outlook rewrites constantly, so syncing it live is rarely reliable.

• Right-click the OneDrive icon, open Settings, and go to the Backup tab
• Under Manage backup, remove the folder that contains the PST from backup if it was added automatically
• Instead, treat the PST as a periodic, one-time file copy rather than a live-synced data file, using Fix 6 to upload a fresh copy when you need a backup

Fix 8: Check File Size Against OneDrive’s Limit

Individual files above OneDrive’s per-file size limit will fail to upload regardless of lock status.

• Right-click the PST file and check its size under Properties
• Compare it against the file size limit for your OneDrive plan
• If the PST exceeds the limit, split the mailbox data into smaller PST files in Outlook using Archive before uploading

Frequently Asked Questions

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