Fix OST File Cannot be Opened Outlook Error in Windows 10/11

OST to PST Converter /March 02, 2025

Microsoft Outlook is a great tool for handling e-mails, appointments, and other contacts for both – private and business use. However, there are times when the users come across the “OST File, Cannot be Opened” error, which hinders access to data. It is a known problem that may affect Windows 10 and 11, making tasks and communication more challenging. This blog post will delve into the causes of this error and give the best ways to correct it.

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

There are numerous reasons why OST files cannot be opened outlook error in Windows 10/11, and here are the most common reasons:

  1. Corrupted OST File: Sometimes, an OST file becomes unusable for some reason, such as an abrupt shutdown of the system. In this case, Outlook cannot open the OST file.
  2. Incompatible Outlook Version: Some Outlook versions do not support the creation and opening of OST files, and using an older Outlook version is one way of making that impossible.
  3. Lack of Synchronization: Sometimes, Outlook may have a problem opening the OST file if the file is not in correct synchronization with the Exchange server.
  4. Large OST File Size: When an OST file is very large, it can, at times, result in slow performance and Outlook not opening it.
  5. Antivirus Interference: At other times, scanning tools such as the antivirus software can affect the OST file and thus hinder Outlook’s interaction with it.
  6. Network Connectivity Issues: Sometimes, Outlook cannot open OST files on the Exchange server due to network connectivity problems or server problems.

Best Solutions to Fix OST File Cannot be Opened Outlook Error in Windows 10/11

Having discussed possible causes, let us consider the best ways to address the “OST File Cannot be Opened” issue. All of the methods that are described in this article work on both Windows 10 and Windows 11.

Method 1: Disable Faulty or Conflicting Add-in

Third-party add-ins can also cause Outlook to perform poorly or have some unexplained glitches in its normal operation. These add-ins can be disabled with the intention of finding out the conflicts that are causing the OST file error. These are the steps one needs to follow in order to disable add-ins

  • Exit Outlook if it is open, and then simultaneously press the Windows key and R.
  • Type Outlook.exe/safe and hit the enter button or click on the OK button.
  • After getting into the safe mode, check whether you are able to open the emails and whether Outlook is capable of synchronizing the mail items with the server.

If Outlook functions correctly in the safe mode, then this suggests that an add-in is a problem for Outlook when opening the OST file. Remove the add-in that is causing the problem in Excel.

  • Navigate to the File tab, click on Options, and then select Add-ins.
  • On the left side of the Outlook Options window, you’ll see the Manage section at the very bottom.
  • Select the option COM Add-ins in the dropdown menu and then click the Go button.

    • Go

  • Select all add-ins and click the OK button.
  • Now, shut Outlook down completely and then launch it again just in the normal window.
  • To isolate the problematic add-in, enable one add-in at a time. When you get to the add-in that is causing the problem, you can then click on the Remove button to delete it from the application.

Method 2: Closing Outlook Processes on Your Computer

There may be Outlook processes that are still running, and these can interfere with the proper running of the application. These background processes might hold onto some resources or prevent new instances of Outlook from being launched correctly. Stopping these processes can assist in eradicating the OST file error since Outlook is left to create a new one.

  • Press Ctrl+Alt+Deleteor Ctrl+Shift+Esc to open the Task Manager.
  • Select Task Manager.
  • Right-click the processes under the Processes tab

    • Ctrl+Alt+Delete

  • Select End Task.
  • Start Outlook.

Method 3: Deleting and Re-Creating the OST File

If the OST file is damaged, one of the solutions is to remove it and let Outlook generate a new OST file. This method is very useful when working with Exchange accounts. The OST file is a local copy of your mailbox, and if it is recreated, then the synchronization problem or corruption problem in the OST file can be resolved.

  • Close Outlook.
  • Locate and remove the OST file.
  • To find the location, in Windows Search type, %LOCALAPPDATA%\Microsoft\Outlook\. Hit Enter. Once you get to the location of the OST file, you should remove it.
  • OST file will be created automatically.

Method 4: Run Outlook in Compatibility Mode

Outlook can be run in compatibility mode to help fix problems relating to the OST file not being able to open. This is particularly beneficial if you have just changed your operating system or if you are using Outlook on your PC is outdated. Compatibility mode enables the application to run in a reduced environment, emulating previous versions of Windows, thus avoiding new configuration problems.

  1. Click with the right mouse button on the Outlook shortcut or the Outlook executable file.
  2. Right-click on one or more properties and select Properties from the list. Click on the Compatibility tab.
  3. Select the “Run this program in compatibility mode for” checkbox and then select the appropriate Windows version from the list.

    4. compatibility mode

  4. After making the changes, click on “Apply” and then ‘OK’ to save the changes made.
  5. Open Outlook and attempt to open the OST file by right-clicking the file and selecting the Compatibility Mode option.

Method 5: Use Goldytools OST to PST Converter

If the above-said manual methods are not helpful in resolving the issue, then it is advisable to use a professional tool such as Goldytools OST to PST Converter. This powerful software is used to fix the OST files that are damaged or corrupted and convert them to PST format. It is particularly useful in conditions of acute corruption or when it is necessary to work with OST data without connecting to Exchange.

Key capabilities of Goldytools OST to PST Converter include

  • The conversion of individual mailbox items.
  • Splitting large PST files.
  • Working with encrypted OST files

This makes it an all-in-one tool for solving not only the “Cannot be Opened” error but also for working with your Outlook information effectively.

Conclusion

It is quite irritating to come across the “OST File Cannot be Opened” error, but this can be solved by following the right procedures. Though manual techniques provide different remedies, they can hardly suffice, especially if corruption is rather profound. However, in such circumstances, it is wise to use Goldytools OST to PST Converter, which could help convert the OST files without much fuss so that the crucial email data can be easily retrievable.

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