Wondershare Repairit
Email Repair

Perfectly repair and recover corrupted Outlook PST & OST files.

  • Fix all Outlook Email issues on Windows and Mac in various scenarios.
  • One trick to fix corrupted PST & OST files in Outlook.
  • Restore Outlook Emails deleted for a long time and extract important Email messages, folders, calendars, etc.
  • Perfectly compatible with Windows & Mac devices.
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Outlook Cannot Open OST File: Causes, Fixes, and More

When encountering the frustrating issue of Outlook not being able to open an OST file, it's essential to understand the underlying reasons for this issue. Various factors can contribute to this problem. Fortunately, there are effective fixes available to address this issue and prevent future occurrences. Let's explore some common reasons for the problem of Outlook cannot open OST and practical solutions to resolve it.

Part 1: Why Outlook Cannot Open OST file?

There can be many common reasons why individuals often cannot open Outlook OST file. To fix the problem, it is vital to know about these reasons.

1. Corrupted OST File: If the OST file gets corrupted due to a sudden system shutdown or other issues, Outlook may not be able to open it.

2. Incompatible Outlook Version: Using an outdated version of Outlook that does not support the OST file format can prevent it from being opened.

3. Lack of Synchronization: If the OST file is not properly synchronized with the Exchange server, Outlook may have difficulty opening it.

4. Large OST File Size: A very large OST file can sometimes cause performance issues and prevent Outlook from opening it.

5. Antivirus Interference: Sometimes, antivirus programs can interfere with the OST file and prevent Outlook from accessing it.

6. Network Connectivity Issues: Poor network connectivity or server issues can prevent Outlook from opening the OST file stored on the Exchange server.

Part 2: Cannot Open Outlook OST File? Try These Fixes

There are many ways to fix the issue when the Outlook OST file cannot be opened. These methods have been proven effective to fix this problem. Those facing this issue should utilize these methods to resolve the problem.

Fix 1: Repair the OST File

  • Repair damaged PST & OST Files in Outlook in all Email corruption scenarios, such as hard disk crashes & bad sectors, virus attacks & tojan horse, outlook corruption & malfunctions, improper shutdown procedure, etc.

  • Restore Outlook Emails deleted for a long time and extract the Email messages, folders, calendars, etc. within seconds.

  • Repair corrupted Emails and restore deleted Emails with a 100% success rate.

  • Repair Emails in bathes without size limits and support to preview all of them before saving.

  • Compatible with Windows 7/8/8.1/10/11, Windows Server 2012/2016/2019, and MacOS X 10.11~ MacOS 12 (Monterey).

Wondershare Repairit is the most reliable OST repair tool available on the market today. It can effortlessly repair corrupt or damaged OST files, ensuring the seamless recovery of your valuable email data. Unlike other repair tools, Repairit employs advanced algorithms to thoroughly scan and extract data from severely corrupt OST files. These are the steps to repair the OST file using the tool:

Step 1: Download and install Repairit for Email software on your computer. Ensure that the software is compatible with your operating system and Outlook version.

selecting ost file to repair

Step 2: Launch Repairit for Email. Click the 'Find' option in the main menu and browse to the location of the corrupted OST file. Select the file and click 'Repair' to initiate the scanning process.

clicking on the find option

Step 3: The software will thoroughly scan the OST file to identify and resolve any errors. Monitor the progress of the scanning process to ensure its completion.

repairit scanning the ost file

Step 4: Once the scan and repair are complete, a preview of the fixed OST file will be displayed. Review the data to verify its integrity. Click the 'Save' button to save the repaired file to the desired location on your computer.

saving the repaired file

Fix Outlook Cannot Open OST Files Issue Now

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Fix 2: Force Close Outlook and Related Processes via Task Manager

If Outlook or its related processes are causing issues, force closing them via Task Manager can help resolve the problem. Here are the steps for this method:

Step 1: Press Ctrl + Shift + Esc to open Task Manager.

task manaer in windows

Step 2: In the Processes tab, locate any processes related to Outlook and select them.

Step 3: Click on the End Task button to force close these processes.

Step 4: Restart Outlook and try opening the OST file again.

Fix 3: Run Outlook in Safe Mode

Running Outlook in Safe Mode can help identify if any add-ins are causing the issue with opening the OST file. To use this method, follow these steps:

Step 1: Press Win + R to open the Run dialog box.

run dialog box in windows

Step 2: Type "outlook.exe /safe" (without quotes) and press ok.

typing the command in the run dialog box

Step 3: Outlook will open in Safe Mode without any add-ins loaded.

Step 4: Try opening the OST file in Safe Mode to troubleshoot the problem.

Fix 4: Disable Add-ins

Disabling add-ins in Outlook can help determine if any of them are causing the Outlook the file OST cannot be opened issue. To apply this method, proceed with the following steps:

Step 1: Open Outlook and go to the File menu, then select Options.

Step 2: Click on Add-ins and then Manage COM Add-ins.

manage add-ins option in outlook

Step 3: Uncheck the boxes next to any add-ins listed and click OK.

unchecking the boxes next to the add-ins

Step 4: Close and restart Outlook to check if the OST file opens without issues.

Fix 5: Run Outlook in Compatibility Mode

Running Outlook in Compatibility Mode can help if there are compatibility issues with the program. These are the steps to fix the problem using this method:

Step 1:Right-click on the Outlook shortcut or executable file.

Step 2: Select Properties from the context menu. Go to the Compatibility tab.

Step 3: Check the box next to "Run this program in compatibility mode for" and select a previous version of Windows from the dropdown menu.

clicking on the box next to run this program in compatibility mode for

Step 4: Click on "Apply" followed by "OK" to confirm the changes.

Step 5: Launch Outlook and try opening the OST file in Compatibility Mode.

Fix 6: Update Outlook

Updating Outlook to the latest version can help resolve any known issues and improve compatibility. To resolve the problem utilizing this method, follow the steps given here:

Step 1: Launch Outlook and navigate to the File menu.

outlook file menu

Step 2: Select Office Account and click on Update Options, then choose Update Now.

Step 3: Outlook will check for available updates and install them.

Step 4: Once the update process is complete, restart Outlook and try opening the OST file again.

Part 3: Tips to Avoid Common OST File Corruption Errors

To avoid common OST file corruption errors, some necessary precautions can be taken. Following these precautionary methods can reduce the chance of the OST file cannot being opened issue from occurring again.

1. Regularly Backup OST files: Create backups of your OST files to prevent data loss in case of corruption.

2. Avoid Abrupt System Shutdowns: Always close Outlook properly to prevent OST file corruption due to sudden shutdowns.

3. Use Reliable Antivirus Software: Ensure your antivirus software is up to date and does not interfere with OST files.

4. Monitor OST File Size: Keep an eye on the size of your OST files and consider archiving older emails to prevent corruption.

5. Maintain Stable Network Connection: A stable network connection is important to prevent synchronization errors that can lead to OST file corruption.

6. Update Outlook Regularly: Keeping Outlook updated with the latest patches and fixes can help prevent OST file corruption issues.


Encountering the file OST cannot be opened issue can be a frustrating experience, but with the right knowledge and solutions at hand, the problems become manageable. You can successfully overcome this issue by understanding the common reasons behind this problem and utilizing effective fixes.

  • 1. Can a large OST file size cause Outlook to be unable to open the file?

  • Yes, a large OST file size can con.ribute to performance issues and may cause the file OST cannot be opened issue. Users can mitigate this problem by archiving old or unnecessary items, compacting the OST file, or utilizing mailbox management policies to keep the OST file size within manageable limits.

  • 2. What role does the Outlook profile play in opening the OST file?

  • The Outlook profile contains settings and configurations that dictate how Outlook interacts with the Exchange server and OST files. If the Outlook profile is corrupted or misconfigured, it can lead to issues with opening the OST file. Users can create a new Outlook profile, delete and re-add the OST file, or repair the Outlook profile to address these issues.

  • 3. Can antivirus software interfere with Outlook's ability to open the OST file?

  • Yes, certain antivirus programs may interfere with Outlook's functionality, including the ability to open the OST file. Users should configure their antivirus software to exclude the Outlook data files from real-time scanning to prevent potential conflicts. It is also important to keep the antivirus software updated to avoid known compatibility issues with Outlook.