Fix Outlook OST File Cannot be Opened on Windows 10/11

Outlook is an advanced email client that offers a wide range of collaboration, messaging, and security features. Still, it can occasionally run into problems and throw errors, such as “Outlook OST file cannot be opened”. This error usually occurs after a specific event, such as Outlook update or reinstallation. In this post, we’ll discuss the reasons behind this error and share some effective solutions to resolve it.

Reasons for Outlook OST File Cannot be Opened Error on Windows 10/11

There are several reasons that can lead to the OST file cannot open error. These include:

• Damaged, inconsistent, or orphaned OST file.
• Problems with synchronizing the mail items to or from the OST file with the Exchange Server.
• Conflicts with other software, such as antivirus or malware programs and firewall.
• Corrupted or damaged Outlook profile.
• Outdated version of Outlook or Windows.

Solutions to Fix the “Outlook OST File Cannot be Opened” Issue

Here are some simple yet effective fixes to resolve the OST data file cannot be opened error.

Method 1: Disable Faulty or Conflicting Add-in

When you open Outlook in safe mode, it loads with minimal functionality and without add-ins and customizations. To start Outlook in safe mode, follow these steps:

1. Close all Outlook processes (if running) and press the Windows + R keys.
2. Type Outlook.exe /safe and press the Enter key or click OK.
3. Once in safe mode, check if you can access the emails and if Outlook is able to synchronize the mail items with the mailbox server.

If Outlook works properly, this means that a faulty add-in is preventing Outlook from opening the OST file. To disable the faulty add-in and fix the Outlook OST file that cannot be opened issue, follow these steps:

• Open the File tab and then go to Options > Add-ins. 
• In the Outlook Options window, find the Manage section at the bottom.

Make sure the COM Add-ins option is selected in the dropdown menu and then click Go.

Unselect all add-ins and click OK.

• Close Outlook and reopen it in normal mode.
• To identify the faulty add-in, enable one add-in at a time. Once you find the add-in that’s causing the problem, you can remove it from the application.

Method 2: Update Outlook and Windows

If you’ve installed an Office update or reinstalled Outlook recently, simply reboot the system. This may help you fix the error. If this is not the case, check for new Office updates and install the available updates. Here’s how:

• Open Outlook.

• Go to File > Office Account (or Account in some versions).

• Under Product Information, select Update Options and then click Update Now.

If the Update Now option is not available in your Outlook client, you can download and install Windows Updates to get the latest bug fixes and updates for MS Office, including Outlook.

Method 3: Reset Navigation Pane

In some cases, the Outlook data file cannot be opened error can occur due to customizations made in the navigation pane. To remove these customizations, open the Windows Run utility (press Windows + R keys) and type Outlook.exe /resetnavpane. Hit the Enter key or click OK.

This will reset the navigation pane and may resolve the OST file cannot be opened error.

Method 4: Repair Outlook

If there is a problem with your Outlook software, you may encounter the OST file cannot be opened error. In such a case, you can repair the Outlook application. Follow these steps:

• Close Outlook and navigate to Control Panel > Programs and Features.
• Select Microsoft Office (or Outlook) from the list and click Change.

• You will see repair options, such as Quick Repair and Online Repair.
• Choose the Quick Repair option and then click Repair.

If the error persists, choose the Online Repair option and then complete the repair wizard.

Method 5: Disable Outlook Compatibility Mode

You can disable or turn off the compatibility mode to check if it is causing the error. The steps are as follows:

1. Type Outlook.exe in Windows search bar and then right-click on it.
2. Choose Properties and then click on the Compatibility tab.
3. Here, uncheck the “Run this program in compatibility mode for” option.
4. Click Apply and then click OK.

If you have Outlook running on Windows 10 or 11, you can run the Compatibility Troubleshooter. For this, right-click on Outlook and choose Troubleshoot compatibility. Continue and complete the wizard to fix the issue.

Method 6: Create a New Profile

By creating a new profile, you can replace the corrupt profile that may be preventing Outlook from opening the OST file. The steps are as follows:

• Close Outlook and open Control Panel.
• Navigate to User Accounts > Mail and click on the Show Profiles button.
• Then, click Add.

• Type any name for this new profile and click OK.

• You will see a sign in the wizard. Enter your email account credentials, such as username (email) and password to log in.
• Once the sign-in is successful, restart Outlook.
• You will see a dropdown from where you need to choose your new profile. Choose the profile and click OK.

Method 7: Rebuild the OST File

The error OST file cannot be opened often occurs when the OST file is corrupt. You can repair the OST file with Outlook’s built-in utility, called ScanPST.exe, which is located in Outlook’s installation directory. However, ScanPST.exe may fail to repair large-sized and severely corrupt Outlook data files. In such a case, you can recreate the OST file. To do so, follow these steps:

• Close Outlook and then go to this location: %LOCALAPPDATA%\Microsoft\Outlook\ 
• You can enter this in the Windows Search bar or Run window (press the Windows +R keys) and press Enter. You will be taken to the folder where the OST is located.
• Once the OST is found, take its backup by copying or renaming it with the .bak extension.
• Then, delete the original OST file from the default location.
• After deleting the OST file, start Outlook. Outlook will automatically recreate the OST file at the default location on your system.

However, sometimes, recreating OST is not possible due to the following several reasons:

• Recreating OST is not possible if the live mailbox is inaccessible.
• If the OST file size is too large, downloading the entire file from the server is problematic or almost impossible.

In such cases, the only option is to recover data from the OST by using an advanced OST converter tool, such as Stellar Converter for OST. The software easily converts the inaccessible OST file to PST, which you can import into Outlook. It converts all the OST file items, including emails, attachments, calendars, contacts, notes, etc. with complete precision. It can also export the OST data to to Microsoft 365 (Office 365). The tool supports Outlook 2021, 2019, 2016, 2013, and earlier versions.

Conclusion

The Outlook OST file cannot be opened error may occur due to missing Outlook update, faulty add-ins, damaged/corrupt OST file, and various other reasons. However, you can easily resolve the error by following the solutions mentioned in this post. In case your OST file becomes inaccessible, you can use an advanced OST to PST converter software, such as Stellar Converter for OST to extract data from such OST file. The software converts OST files into Outlook PST format which can be easily imported into any Outlook account.

Also Read

• Error [Solved] OST is not an Outlook Data File
• Error Solved: “The file username.ost is in use and cannot be accessed” in Outlook

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About The Author

Abhinav Sethi

Abhinav Sethi is a Senior Writer at Stellar. He writes articles, blog posts, knowledge-bases, case studies, etc. for different technologies. He also has a keen interest in digital forensics and helps forward-thinking companies fight different threats with apt solutions.