Email Sync Problems

How to Repair an Outlook OST File That Cannot Be Opened

Camila Milosovich Oct 1, 2026 869 views

Question details

The user needs to fix an inaccessible Outlook OST data file that is preventing the desktop email client from opening or synchronizing.

How to Repair an Outlook OST File That Cannot Be Opened

Product: Microsoft Outlook
Device & OS: Windows
Scenario: Attempting to launch the Microsoft Outlook desktop application to access local mailbox data.
Observed behavior: Outlook fails to launch and displays an error message stating that the OST data file cannot be opened, even though webmail access continues to work.

Before you start

Before proceeding, log in to Outlook on the web to confirm that your emails are still safely stored on the Exchange server. Ensure the Outlook desktop application is completely closed.

Solution 1Recommended

Recreate the Local OST File

Because an OST file is simply a local cached copy of your server mailbox, the safest and most reliable fix is to delete it and let Outlook build a fresh copy.

This method is highly recommended for Exchange, IMAP, and Outlook.com accounts. When the old file is removed, Outlook automatically downloads your data directly from the server the next time it starts, eliminating local corruption issues.

Close Outlook completely

Ensure that Microsoft Outlook is fully closed. You may need to check the Task Manager (Ctrl + Shift + Esc) to verify that no 'OUTLOOK.EXE' processes are running in the background.

Navigate to the OST file location

Press the Windows key + R to open the Run dialog. Type '%localappdata%\Microsoft\Outlook' into the box and press Enter to open the folder containing your data files.

Rename or delete the corrupted file

Locate the file with the '.ost' extension that corresponds to your email address. Right-click the file and select 'Rename' (change it to something like 'old_profile.ost') or select 'Delete'.

Restart Outlook to synchronize

Open Microsoft Outlook. The application will automatically create a new OST file and begin synchronizing your emails and folders from the mail server.

Data Safety: Your emails, calendar events, and contacts are stored on the server. Deleting the OST file will not result in permanent data loss.

Solution 2

Start Outlook in Safe Mode to Test Add-ins

Sometimes a corrupted or conflicting third-party add-in prevents Outlook from properly accessing the OST file.

Solution 3

Run an Office Installation Repair

If recreating the OST file and disabling add-ins does not work, the Microsoft Office installation itself might be damaged.

Free Microsoft Office alternative

Tired of Persistent Microsoft Office Errors? Try WPS Office

If you are frustrated by recurring data file corruption, sync issues, or complex technical errors in Microsoft Office, consider switching to WPS Office. It provides a lightweight, highly compatible, and user-friendly alternative for all your document, spreadsheet, and presentation tasks—completely free of charge.

1. Download the Installer: Visit the official WPS Office website and download the free, lightweight installation package.
2. Install in Seconds: Run the installer and follow the quick setup wizard to get WPS Office running on your device.
3. Open Your Files Directly: Drag and drop your existing docx, xlsx, or pptx files into WPS Office to immediately start working with full formatting compatibility.

Free to use with a lightweight installation that won't bog down your systemFully compatible with Microsoft Word, Excel, and PowerPoint file formatsIntuitive tabbed interface that keeps all your documents in one clean windowReliable cloud synchronization without the hassle of easily corrupted local cache files

microsoft office alternative - wps office

Frequently Asked Questions

Should I use ScanPST.exe to repair my OST file?

While the Inbox Repair Tool (ScanPST.exe) can technically scan OST files, it is primarily designed for PST (Personal Storage Table) files. For OST files, the most effective and Microsoft-recommended solution is to simply rename or delete the file and let Outlook rebuild it from the server.

Why does my email work on the web but not in the Outlook desktop app?

Outlook on the web accesses your mailbox data directly from the live Exchange or cloud server. The desktop app relies on an offline cache file (the OST). If this local file becomes corrupted or out of sync, the desktop app will fail to open, even though your actual server data remains unharmed.

What happens to my local folders if I delete the OST file?

If you have data saved in local folders labeled 'This computer only' (common with some IMAP setups) that hasn't synced to the server, that specific data might be lost when the OST is deleted. It is always a good idea to back up or export those specific folders if you can access them before deleting the OST.

What should I do if recreating the OST file doesn't fix the issue?

If Outlook still refuses to open, the issue might lie with a corrupted Outlook profile rather than just the OST file. You can create a fresh profile by opening the Windows Control Panel, searching for 'Mail', clicking 'Show Profiles', and adding a new profile with your email credentials.

Outlook & Email Problems