How To Fix Outlook OST File Cannot Be Opened?

Are you facing the Outlook data file that cannot be opened for the OST issue on your computer? This may cause a loss of access to essential data from your Outlook mailbox, including emails and contacts.

Quick Solution for OST File Cannot Be Opened

Download this Outlook repair app and follow the steps inside the tool to repair your cannot opened OST files.

Outlook OST files automatically synchronize a copy of your emails, contacts, calendar data, and other data for offline use when you cannot connect to your mail server, such as in case of a bad internet connection.

However, users have often encountered issues when their Outlook data file cannot be opened. OST files, like all other data files, are susceptible to corruption and other damages.

If you are facing a similar issue, head below to discover the reasons behind the issue and how to get rid of it easily using effective methods.

Part 1: Why Doesn't Outlook OST File Open?

Following are a few plausible reasons why your Outlook OST cannot be opened.

1. Synchronization Errors

If the network connections on your device are not working normally, or the OST file and the Exchange server are not properly synchronized, it can cause the Outlook OST files to become inaccessible.

2. Forceful Closure of MS Outlook

If you try to close your MS Outlook application or a data file abruptly or forcefully, it can cause severe damage to the file and render your Outlook OST inaccessible.

3. Orphaned OST Files

When your Exchange profile is inactive or disconnected from the Exchange server, it can halt the synchronization process. Because the data file is not permanently linked with the server, such files are referred to as orphaned files. If this is the case, your Outlook OST file will not open.

4. Virus or Malware

Like all data files, Outlook OST files are prone to virus and malware attacks. One of the most common reasons you cannot access your OST file is because of corruption or damage due to a likely virus attack.

5. Electrical Surges

When sudden and abrupt electrical surges or an unexpected power failure occurs, your Outlook OST file can corrupt and become inaccessible.

Part 2: Methods on How to Fix OST File That Cannot Be Opened

Despite why your Outlook OST cannot be opened, the issue remains unsolved. So, here are some simple yet effective methods to fix your Outlook OST files instantly and without much trouble.

Method 1: Outlook Process Terminations on Computer

You can try to fix your Outlook OST files issue by ending the ongoing Outlook processes on your computer. You can do this by following these steps:

Step 1: Open Task Manager on your computer. You can do this either by right-clicking on the taskbar and clicking on "Task Manager" or pressing “Ctrl+Alt+Delete” on your keyboard and selecting “Task Manager” from the list.

open task manager

Step 2: Now go to the “Processes” tab in the Task Manager popup window.

Step 3: In there, you can search for processes named "Communicator," "Lync," "ucmapi," or "Outlook." If you find any of these, tap and click on the "End Task" button.

end outlook tasks

Method 2: Unchecking Cache Exchanged Mode Option

If you cannot open the OST file on Outlook 365, you can disable your system's cache exchange mode option. Here are the steps indicating how to do that:

Step 1: To begin with, you need to close any opened Outlook window. Now, search for “Control Panel” on your Windows search bar and enter. Once inside the control panel, search for the “Mail” option.

open mail setup

Step 2: From the “Mail Setup” dialogue box, tap on the “Email Accounts” button at the top.

access email accounts

Step 3: An “Account Settings” dialogue box will appear on the screen. Locate the email account linked with your inaccessible OST file and hit the “Change” button.

tap on change account option

Step 4: Your system will open a “Change Account” window. Deselect the checkbox next to the “Use Cached Exchange Mode” option. Tap on “Next” and finish the process.

disable use cache exchange mode

Method 3: Disable Problematic Add-Ins

Sometimes, conflicting add-ins within the Outlook application can cause Outlook OST to become inaccessible. Here is how you can fix that:

Step 1: Hit the “Windows+R” keys on your keyboard to launch the “Run” utility. Type “outlook.exe/safe” in the window and click "OK." Your Outlook application will now launch in safe mode.

launch outlook in safe mode

Step 2: Go to the "File" tab in Outlook and navigate to "Options." From here, find and click on "Add-ins."

access add-ins

Step 3: In the Add-ins window, locate the "Manage" section and ensure that the dropdown list reads as "COM Add-ins." Then hit "Go."

tap on go button

Step 4: Deselect all the add-ins from here and then select "OK." You can now relaunch Outlook normally and see if the error is resolved. You can identify the problematic add-in by enabling them one by one and see which one was causing the issue.

disable outlook add-ins

Method 4: Ruling out Compatibility Mode

If your Outlook OST cannot be opened, you can turn off compatibility mode from your computer settings. Here is how to do that:

Step 1: Click on the Windows button to open the Start menu. Search for "outlook.exe" and right-click on it to select "Properties."

open outlook properties

Step 2: Go to the “Compatibility” tab and deselect the box next to the “Run this program in compatibility mode for” option. Now click on “OK” and reboot your system to get rid of the issue.

turn off compatibility mode

Bonus Tip: Wondershare Repairit for Email Ultimate Method to Repair PST Files

Similar to an OST file, a Personal Storage Table (PST) is an Outlook data file that saves your mailbox information on your computer. PST files can be used to back up, import, or export data such as emails, contacts, calendars, etc., from your email account.

Unfortunately, PST files are no stranger to corruption or data loss. Losing your PST file can lead to potential data loss from your email account. If you are dealing with a corrupted or damaged PST file, you can repair it using data repair software such as Wondershare Repairit for Email.

Repairit for Email is a data recovery program that can repair and retrieve data from various corrupted file formats. You can use it to recover your essential mailbox data, including email messages, attachments, tasks, and more, from an inaccessible PST file. The tool supports almost all versions of Outlook and guarantees a 100% precision rate with its comprehensive toolset.

Key Features of Repairit for Email:

  • 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 very high 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).

How to Repair PST Filer Using Repairit for Email.

Once you have installed Repairit for Email on your computer, you can follow the steps below to recover your PST files:

Step 1: Upload the corrupted Outlook file.

After launching Repairit for Email, you can select a scan option from the program's interface. The "List Profiles" option will automatically dictate the data files on your Outlook account. By clicking the "Choose Manually" option, you can browse your computer to look for lost data files or tap "Find" to let the tool find the file automatically.

upload file

Step 2: Initiate Repairing

Once you have selected your desired PST file, click on “Repair” to let the program scan and repair the selected Outlook data file.

start repair pst file

Step 3: Preview and save Files

After Repairit completes the repair process, you can preview all the recovered mailbox items, such as emails, on the screen, then click on “Save” to select a desirable location to save your fixed PST file.

preview recovered files


Outlook OST files serve significant advantages to users in unprecedented events. OST files allow users to access their mailbox data such as emails and tasks when offline. If an error occurs in the Outlook OST data file, there is a chance you can lose your important data.

Luckily, you can fix your Outlook OST cannot be opened issue easily with the practical and quick solutions mentioned above. If you are suffering from corrupted or inaccessible PST files, you can repair them easily using Repairit for Email.