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Resolve Microsoft Outlook OST File Cannot Be Opened Issue

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Published By Jamie Kaler
Rollins Duke
Approved By Rollins Duke
Published On May 9th, 2025
Reading Time 8 Minutes Reading

If you are facing Microsoft Outlook OST file cannot be an error , it can disrupt workflow, prevent access to crucial important, signal underlying issues ranging from file corruption to profile misconfigurations. Whether you’re using Outlook 2016, 2019, or Outlook from Microsoft 365 this issue can arise unexpectedly.

Microsoft Outlook is one of the most widely used email clients in both personal and professional communication. It contains mailbox data in OST and PST file. OST file allows to store emails, contacts, calendars when they’re offline. However, users sometimes encounter frustrating errors such as “Outlook OST file cannot be opened”.

In this tutorial, we will explore what causes this error, walk through proven methods to fix it, and after preventive tips to avoid facing these issues in the future – all with a focus on helping you get your Outlook back to working order.

Table of Contents Hide
  1. Difference between OST and PST files
  2. Common Causes of the “OST File Cannot Be Opened” Error
  3. Preparation Before Fixing
  4. Methods to Fix “OST File Cannot Be Opened” Error
  5. Alternative Method to Fix Microsoft Outlook OST File Cannot Be Opened Issue
  6. Preventive Measures to Avoid OST File Errors
  7. Mostly Asked Queries by Users
  8. Takeaway

Difference between OST and PST files

Feature OST(Offline Storage Table) PST(Personal Storage Table)
Usage Used with Exchange, IMAP, and Microsoft 365 accounts Used for POP3 accounts or exported backups
Location Stored locally and synced from the server stored locally, not synced automatically
Offline Access Provide access to mailbox data without connectivity Provide access to exported data offline
Synchronization Automatically sync changes with the server No synchronization with the mail server
Creation Created automatically by Outlook when you set up an Exchange or IMAP account. Created manually for backups or data export
Best use case For users who need offline access to server-based mailboxes For archiving or transferring Outlook data

Common Causes of the “OST File Cannot Be Opened” Error

  • Sometimes, OST files get corrupted due to unexpected closure, power failures, or bad factors in the hard drive. Once corrupted, Outlook may fail to open the file, displaying this common error.
  • If Outlook fails to connect an OST file with Exchange Server due to connectivity issues or it can make the OST file inaccessible.
  • Some add-ins not supported Outlook due to incompatible or updated versions cannot access the OST file correctly.
  • Using older versions of Outlook shows compatibility issues, bugs or unpatched errors that affect OST files and are not able to be opened.
  • A corrupt or misconfigured Outlook profile can interfere with Outlook loads data from an OST file. In this situation, the program fails to load or connect properly.
  • Sometimes, another program or background process(such as antivirus software)may lock the OST file preventing Outlook from accessing it. This often happens silently and can be resolved by closing conflicting applications or restarting the system.

Preparation Before Fixing

  • Sometimes, Outlook continues to run in the background even after being closed. A sync process may keep the OST file locked and inaccessible.
  • If multiple Outlook windows or background processes are open, they can prevent OST files from loading properly.
  • A reboot can release a system or application that locks the OST file and clears my temporary issues interfering with Outlook’s operation.
  • Real-time protection tools can sometimes lock or scan OST files, blocking Outlook access. Disabling the antivirus briefly can help identify that if it’s the cause.
  • For Exchange or IMAP accounts, Outlook requires a stable connectivity to the mail server. A poor or disconnected network can trigger OST file access errors.

Methods to Fix “OST File Cannot Be Opened” Error

If your preliminary checks didn’t resolve the issue, the following methods can help to fix Outlook OST File cannot be opened error. Try these solutions as we have shared below:

Method 1. Update Outlook and Windows

  1. Microsoft Outlook can cause compatibility issues with the OST file.
  2. Ensure Outlook and Windows are updated to the latest version.
  3. Updates often include bug fixes that resolve file access problems.

Method 2. Start Outlook in Safe Mode and Disable Add-ins

  1. Launch Outlook in safe mode by pressing Win+R and type Outlook.exe/safe and hit Enter.
  2. If Outlook opens successfully, Go to file and click on Options.
  3. Press on Add-ins and disable Non-Microsoft add-ins.

Method 3. Repair Outlook Profile

  1. Go to the Control Panel and click on Mail.Open Control Panel
  2. Press on Show Profiles and create a New Profile.Click on Show Profiles
  3. Set as default and open Outlook using the new Profile.Set as default

Method 4. Use Inbox Repair Tool

  1. Locate and run ScanPST.exe(usually found in Outlook installation directory).ScanPST Repair Tool
  2. Select the OST file and follow the prompts to scan and repair.Select OST file

Method 5. Recreate OST File

  1. Close Outlook and navigate to OST file location.Open OST location
  2. Delete or rename OST file.
  3. Restart Outlook – Outlook will automatically create a new OST file.Relaunch Outlook
Method 6. Disable Cached Exchange Mode
  1. Go to file and click on Account Settings and press on the Email tab.Click on Account Settings
  2. Double click on your account and uncheck Use Cached Exchange Mode.
  3. Relaunch Outlook and check if the issue is resolved.
Alternative Method to Fix Microsoft Outlook OST File Cannot Be Opened Issue

If your OST file gets orphaned then we recommend you to opt MailsWare OST Converter as this software allows to restore and convert corrupted, damaged and orphan OST files and offers a healthy OST file with maintained attributes. This software has been designed with a tried and tested solution to get accurate results without losing any information.

Steps to Fix Microsoft Outlook OST File Cannot Be Opened Issue
  1. First, Download and open automated software on your system.Resolve Microsoft Outlook OST File Cannot Be Opened
  2. After that, Click on configured Outlook mailbox data and select Recovery Mode.Click on configured Outlook mailbox data
  3. Now, Choose the OST mailbox folder or subfolder as you wish to convert.Select OST mailbox folder
  4. Here, Browse the PST file in the list of Saving options.Choose PST
  5. Thereafter, Choose PST file size and select your preferred language.Select PST size
  6. Select advanced filter and press Convert to fix Outlook OST file cannot be opened error.Start Resolve Microsoft Outlook OST File Cannot Be Opened
Why Opt for an Automated Solution instead of Manual Methods?
  • This software can convert OST to PDF, MBOX, HTML, EML and 25+ Saving features.
  • It offers a user-friendly interface to easily perform by any professional or individual users.
  • You can also restore and convert damaged, corrupted, inaccessible and oversize OST files.
  • With this wizard, you can also use advanced filters such as create PST year wise, date range, subject, sender, exclude folder, skip empty folder and many more as per required.
  • This solution can also import OST to Gmail, Thunderbird, Zimbra, Microsoft 365, and all IMAP supported servers.
Preventive Measures to Avoid OST File Errors
  • Keep software up to date for latest bug fixes, advanced security and away from compatibility issues to keep healthy OST file.
  • Unexpected closing Outlook or system shutdown without properly closing the app can damage the OST file. Always close Outlook properly before restarting or shutting down your computer.
  • Although OST file synced the server, if wise to regularly convert OST to PST for backup. This can be crucial if you need to restore emails during server issues or OST corruption.
  • Large mailboxes can increase risk of synchronization errors and OST corruption. Archive old emails, empty deleted items and use Outlook’s built-in tools to reduce OST file size.
Mostly Asked Queries by Users

Why is Outlook saying the file cannot be opened?

Outlook says the file cannot be opened due to the OST file being corrupted, locked by another process if there are issues with your Outlook profile, add-ins or synchronization with the mail server.

Why is my OST file not being recognized?

As an OST file not being recognized due to corruption, file system errors or profile mismatches. It can also happen if an OST file was created under Outlook profile or if its being accessed on a different system.

How do you fix an issue with Outlook not opening?

To fix Outlook not opening, start in Safe Mode, disable add-ins, update Outlook, repair your profile or recreate the OST file. If needed, use a repair Tool like ScanPST or professional OST Recovery utility.

Takeaway

In this article, we have shared the overview and reasons for Microsoft Outlook OST File Cannot Be Opened. After knowing reasons, it mostly happens due to Outlook updates, faulty add-ins, or OST files getting damaged or corrupted. If OST is active then you can go with a manual approach. If manuals don’t work then we recommend you to opt for automated software as it can restore and fix OSTs that cannot be opened without losing any single bit of information.

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