How to Fix “Outlook.OST Cannot Be Opened” Error In Microsoft Outlook

Last updated on January 5th, 2023 at 02:44 pm

Searching for a solution to resolve the “Outlook.ost cannot be opened” error in Microsoft Outlook? Your work is done! In this article, you are going to discuss the best solution to easily resolve this error to regain your OST file database in Outlook.

Microsoft Outlook is an email client, available as a part of the Microsoft Office suite. Outlook creates OST files, to store the user’s mailboxes on their local machine. Outlook requires a connection with Exchange or IMAP Server to preserve managing data in OST files.

Get the straight-forward solution to Reapir all corruption errors from Outlook OST, backup OST file & Convert OST to PST with eSoftTools OST to PST Converter Software.


But sometimes, while using Outlook users faces some errors. One of those Outlook errors is – “outlook OST file cannot be opened“. Before going into the process of fixing this error first let’s see “what are the reasons for this error in MS Outlook“.

Reasons for the “Outlook OST Cannot Be Opened” error:

Here are some reasons that cause this error and create problems in Outlook functioning: –

  • The first reason behind this “outlook cannot open OST file” error is improper MS Outlook application installation. Any problem with installation will not allow the files to open correctly.
  • Unexpectedly termination of MS Outlook when the OST file is in use.
  • Sometimes this problem comes due to issues in synchronization between OST file and the server.
  • When outlook is deleted from the computer and your OST file is left orphaned.
  • Virus or malware infection can cause corruption in Offline OST files.
  • The oversizing OST file is also a reason for the error “outlook OST cannot be opened“.

Have a look at each of the mentioned reasons, and see which one is causing an issue for you. Once getting all the reasons, now move to the part of the solution for these reasons.

Manual Methods to Fix “Outlook.ost cannot be opened” error:-

  • Close the MS Outlook program.
  • Launch the Task Manager on your computer.
  • Go to the Processes tab.
  • Now, in the Processes tab, look for the processes Communicator, Sync, Outlook, or MAPI. If any of these processes are found, select it and click on the End Process button.

Method 2: Disable Outlook Cached Exchange Mode

  • Close MS Outlook and go to the control panel.
  • Click on the Mail option and then select Email Accounts.
  • Under the Email Accounts, hit on the Email tab.
  • Now click on Exchange account and then hit on Change.
  • Uncheck the “Use Cached Exchange Mode” option under offline settings and hit Next to finish the process.

Method 3: Disable the Outlook Add-ins

To improve the functionality of Outlook most users use third-party add-ins. But faulty add-ins may sometimes create some trouble and may also cause Outlook errors. Thus, disabling the add-ins by launching Outlook in safe mode can be a solution to fix this error. Do this by just typing “outlook /safe” in the Run dialog box. Try “Save and Send” and if it works, a faulty add-in is the main reason behind the error. You can also start Outlook in safe mode by following the below-mentioned steps:

  • Go to the shortcut icon for Outlook.
  • Now, press and hold the CTRL key and double-click the application shortcut.
  • Click ‘Yes’ when a window prompt appears asking if you want to start the application in Safe Mode

Method 4: Repair OST file with ScanOST.exe

Microsoft Outlook offers an inbuilt ‘OST Integrity Checker’ tool also known as ScanOST.exe which helps to rectify minor corruption problems in OST files. For repairing Outlook OST files users can use ScanOST.exe and fix this “Outlook.ost cannot be open” error.

Follow the below steps to resolve OST error:-

  1. Exit from MS Outlook and navigate to the directory on your system where Outlook has been installed. Now, navigate to the ScanOST.exe location and double-click on it to launch this utility.
  2. The application will prompt you to select the OST file for repair. Click on the Browse button and select the OST file from its location.

    Note:- If you don’t know its exact location, you can find it by typing the following in the Run dialog:

  3. Click on the “Begin Scan” option to automatically check and remove the errors in the OST file.

Limitations of manual methods

  • The manual methods are time-consuming.
  • It is a hard task for non-technical users as it requires some technical knowledge.
  • It doesn’t ensure security for data as well.
  • Not a 100% guaranteed solution to repair Outlook corruption errors

Solution to Resolve Error “Outlook.OST Cannot Be Opened”

Users who don’t want to use any manual method or a long process to repair Outlook OST errors, then they must an automated tool. The best utility for users to resolve OST errors is eSoftTools OST Recovery Software. It is an effective method for users to repair OST by saving their time and effort. It ensures data protection while fixing the error of Outlook OST files. The best benefit of this tool is, it repairs OST files with complete safety as well as security.



In this article, we have shown all the possible ways to fix the error “Outlook.ost cannot be open”. Applying manual tricks users can resolve Outlook errors but with them, users may face data loss issues. So, users should go with the automated software to resolve outlook.OST errors.

eSoftTools OST Recovery tool is the best solution and it provides the best result to users. It saves your time & effort and performs the repair process with ease.

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