How to Repair OST File - A Complete Guide

Jan 12, 2024 | By Deepak Singh Bisht

Understanding and managing data is crucial in our digital world, and one common challenge faced by Microsoft Outlook users is dealing with OST files. Offline Storage Table (OST) allows you to work offline and then synchronize updates with the Exchange Server the next time you connect to the internet. However, like any file, OST can become damaged or corrupted, rendering them inaccessible. In such situations, you might find yourself asking, "How to repair OST file?" This blog post aims to guide you through this process in an easy-to-understand manner.

What is an OST File?

An OST file, or Offline Storage Table file, is a critical component in Microsoft Outlook, widely used by various individuals and organizations. These files are integral to the functionality of Outlook, particularly when operating in environments connected to Microsoft Exchange Server or IMAP email accounts. Let's explore what OST files are, their role in Outlook, and their significance.

The nature of OST files

OST files are unique data files created by Microsoft Outlook. They are essentially a local copy of a user's mailbox stored on the Exchange server. This file format is utilized by Outlook to enable users to work offline, or when the connection to the Exchange server is intermittent or unreliable.

How OST files function in Outlook?

The primary function of an OST file is to allow users to continue working with their emails, calendar entries, tasks, and other Outlook items even when not connected to the Exchange server. Users can compose emails, schedule appointments, and make changes to tasks. These changes are then synchronized with the Exchange server once the user is back online. This functionality is particularly valuable for users who travel frequently or have limited internet connectivity.

The importance of OST files

Offline accessibility: OST files enable access to email data even when offline. Users can read emails, draft responses, and organize their mailboxes without an active internet connection.

Synchronization: Once reconnected to the Exchange server, all changes made offline in the OST file are automatically synchronized, ensuring that the mailbox on the server is updated with the latest changes.

Backup and recovery: In some scenarios, OST files can be used as a backup. They contain all the data stored on the Exchange server, which can be useful in data recovery situations, such as server crashes.

Data security: OST files ensure that a user's mailbox data is stored locally, providing an additional layer of data security and accessibility.

Reduced server load: By allowing users to work offline, OST files reduce the load on the Exchange server, as data synchronization occurs only when the user reconnects to the network.

OST files are an essential aspect of data management in Microsoft Outlook, especially for users who require consistent access to their email and other Outlook items regardless of their connection status to the Exchange server. These files ensure seamless data synchronization while providing a reliable means of working offline, highlighting their indispensable role in the modern digital workflow.

Why OST files get corrupted?

As beneficial as OST files are, they are not impervious to problems. These files can be corrupted or damaged due to a variety of reasons, leading to accessibility issues. Here are some common causes of OST file corruption:

Virus or Malware Attacks: Viruses and malware can corrupt files, including OST files. Once infected, these files can become unreadable or inaccessible.

Abrupt Termination of Outlook: If Microsoft Outlook is closed abruptly while an OST file is being written to or updated, this could lead to the corruption of the file.

Power Outages: Sudden power outages when an OST file is open and in use can lead to corruption.

Hard Drive Failures: If the hard drive where your OST files are stored fails or suffers from bad sectors, this can lead to OST file corruption.

Network Connection Issues: Since OST files synchronize with the Microsoft Exchange Server, any interruption or issues with the network connection during this process could potentially damage the OST files.

Software or Hardware Conflicts: Issues with hardware or software can cause OST files to become corrupt. This could be due to problems with your computer's operating system, conflicts with other software, or faulty hardware components.

Oversized OST Files: In older versions of Outlook (2002 and earlier), OST files have a size limit of 2GB. If this limit is exceeded, it can cause the file to become unstable and eventually corrupt.

Understanding the causes of OST file corruption is crucial as it can help you take preventive measures to protect your valuable data. When an OST file becomes corrupted, it can lead to errors, and you may be unable to access your emails and other data. In the worst-case scenario, you may lose all your data.


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How to repair OST file?

When an OST file gets corrupted, there are a couple of standard methods available to repair and restore it. The two primary approaches include manual methods and the use of third-party OST repair tools.

The manual methods usually involve built-in features of the Outlook application, like the Inbox Repair Tool (ScanPST.exe), or recreating the OST file. While these methods can be effective, they can also be quite technical and might not always recover all your data.

On the other hand, third-party OST repair tools often provide a more user-friendly interface and offer more advanced recovery options, making them a popular choice for many users to repair OST files.

Here, we will delve into each of these methods in detail, providing step-by-step instructions to guide you through the process of repairing OST files.

Note: Before using any manual method or third-party Outlook OST Repair tool, create a backup.

Method 1: Repair OST file using Inbox Repair Tool

The Inbox Repair Tool (Scanpst.exe) provided by Microsoft is designed to repair errors in Outlook data files, including OST files. It scans the file for inconsistencies or errors and attempts to fix them to regain access to your data.

Note: Before starting the inbox repair tool, create a backup.

Steps to follow:

1. Close MS Outlook and navigate to one of the following file locations, then double-click on SCANPST.EXE to open it.

  • Outlook 2019: C:\Program Files (x86)\Microsoft Office\root\Office16
  • Outlook 2016: C:\Program Files (x86)\Microsoft Office\root\Office16
  • Outlook 2013: C:\Program Files (x86)\Microsoft Office\Office15
  • Outlook 2010: C:\Program Files (x86)\Microsoft Office\Office14
  • Outlook 2007: C:\Program Files (x86)\Microsoft Office\Office12
Displaying file location paths for SCANPST.EXE

2. Once the tool is open, click on the 'Browse' button.

Opening SCANPST.EXE tool in Outlook.

3. Select the damaged OST file you wish to repair and click on the 'Open' button.

Browsing for damaged OST file in SCANPST.EXE.

4. After selecting the file, click on the 'Start' button.

Initiating file repair with Start button in SCANPST.EXE.

5. SCANPST.EXE will then check the file for consistency and issues.

SCANPST.EXE checking file consistency.

6. If SCANPST.EXE detects errors, choose the 'Make backup of scanned file before repairing' option, select a backup location, and click 'Repair' to start the repair process.

Selecting backup option in SCANPST.EXE before repair.

7. Upon completion, a 'Repair Complete' popup will appear; click 'OK' to conclude the process.

Repair Complete notification in SCANPST.EXE.

After the process, you might see the Recovered Personal Folders or Lost and Found folder. These folders contain your missing folders and items. To place the items in the original folder structure, you can select items, and after that, drag the selected items and drop them into the original folders.

When to use:

  1. For minor errors and inconsistencies in your OST file.
  2. When Outlook is experiencing issues opening, or you're receiving error messages related to the OST file.
  3. As a first step in OST file troubleshooting, before trying more complex solutions.

Method 2: Repair Outlook OST file by deleting and recreating the OST file

This method involves deleting the corrupted OST file and allowing Outlook to recreate a fresh copy. This process can resolve issues caused by OST file corruption.

Steps to follow:

1. Open MS Outlook and navigate to the File menu.

Accessing File menu in MS Outlook

2. Choose 'Account Settings' and then select the 'Account Settings' option.

Selecting Account Settings in MS Outlook.

3. The Account Settings window will open, displaying your currently connected email accounts.

Display of connected email accounts in Outlook Account Settings.

4. Click on the 'Data Files' tab and select the OST file you wish to recreate.

Choosing OST file under Data Files tab in Outlook.

5. Choose the 'Open File Location' option to view the OST file's location.

Opening OST file location from MS Outlook.

6. After locating the OST file, close MS Outlook.

7. Identify the OST file you intend to recreate.

Identifying OST file for recreation in Outlook.

8. Right-click on the chosen OST file and select the 'Rename' option.

Renaming OST file in file explorer.

9. Append the .bak extension to the end of the OST file name and press the Enter key.

Adding .bak extension to OST file name.

10. Reopen MS Outlook.

Reopening MS Outlook for setup.

11. Outlook will automatically recreate the OST file.

Automatic recreation of OST file in Outlook.

When to use:

  1. When the Inbox Repair Tool is unable to fix the OST file.
  2. If the OST file is too damaged for standard repair methods.
  3. After ensuring that all your data is synchronized with the Exchange server to prevent data loss.
  4. Particularly useful when facing synchronization issues or severe file corruption.

Note: This method pulls data from the MS Exchange server. It cannot restore Outlook items that you created in Offline mode and was not synched with MS Exchange.

Method 3: Fix OST file by disabling and re-enabling Cached Exchange Mode

Cached Exchange Mode in Outlook allows you to work offline with a copy of your mailbox. Disabling and then re-enabling it can reset the synchronization with the Exchange server, potentially resolving issues.

Steps to follow:

  1. Close Outlook and go to Control Panel > Mail.
  2. Click on Email Accounts and select your Exchange account.
  3. Uncheck the option 'Use Cached Exchange Mode'.
  4. Apply the changes and reopen Outlook to let it synchronize.
  5. Repeat the steps and re-enable Cached Exchange Mode.

When to use:

  1. When experiencing synchronization problems between Outlook and the Exchange server.
  2. If new emails aren't appearing in Outlook or changes aren't syncing.
  3. After encountering errors suggesting problems with the OST file's integrity.

Method 4: Repair OST file using the OST Integrity Check Tool (Scanost.exe)

Scanost.exe was a tool available in older versions of Outlook (up to 2007) designed to check and repair issues within OST files. It's less powerful than Scanpst.exe but useful for minor integrity issues.

Note: This tool is not available in newer versions of Outlook.

Steps to follow:

  1. Close Outlook and locate Scanost.exe (usually in the same directory as Scanpst.exe).
  2. Run the tool and select the profile containing the OST file.
  3. Choose the option to repair errors and start the scan.

When to use:

  1. With older versions of Outlook (2007 or earlier).
  2. When experiencing minor issues with OST files, like minor synchronization errors.

Method 5: Repair Outlook OST File by Resetting Outlook Profile

Creating a new Outlook profile can resolve issues caused by a corrupt profile. It essentially resets Outlook's settings and files, potentially fixing problems related to the OST file.

Steps to follow:

  1. Close Outlook and go to Control Panel > Mail.
  2. Click on 'Show Profiles'.
  3. Add a new profile and configure it with your email account.
  4. Set the new profile as the default profile.
  5. Restart Outlook and check if the issues are resolved.

When to use:

  1. If problems persist even after repairing the OST file.
  2. When Outlook continuously crashes or fails to start.
  3. If OST-related errors continue after other repair attempts.

Method 6: Fix OST file utilizing Windows System Restore

Windows System Restore can revert your system to a previous state where Outlook and the OST file were functioning correctly. It's helpful if a recent system change caused the OST file issues.

Steps to follow:

  1. Go to Control Panel > System and Security > System.
  2. Click on System protection and then System Restore.
  3. Follow the prompts to choose a restore point before the issue started.

When to use:

  1. After a software installation or system update coincides with the start of OST file problems.
  2. If changes to system settings have affected Outlook's performance or file integrity.
  3. As a last resort when other methods haven't resolved the issue.

Method 7: Repair OST file using OST Repair Tool

If your OST file is still inaccessible after trying the above methods, you might consider using a third-party Outlook OST Repair tool like SysCurve OST to PST Converter to repair OST file. This software is designed to repair and recover damaged OST files and convert them into PST format, making your data accessible in Microsoft Outlook.

  1. Download and install the OST Repair tool
  2. Click on the Add file and select the OST file which you want to repair
  3. Click on the Scan button and click on the OK button
  4. After the process, the software will generate a preview mode inside the software
  5. Click on the Export and choose the Export All folders option
  6. Select PST (Outlook data file) as an Export option and provide a destination path
  7. Click on the Next button to start the conversion process

After the process, you can open the converted PST file with MS Outlook.

Other helpful features

  • Quickly repair OST files
  • Convert OST to PST, EML, MBOX, HTML, RTF, and other file formats
  • Migrate OST to Office 365 and Live Exchange server
  • Maintain original hierarchy folder structure
  • Perform selective conversion based on To, From, Subject, Cc, Date range, etc.
  • Free conversion or migration for the first 20 items per folder
  • Support Windows OS and all versions of MS Outlook

Frequently Asked Questions

What can cause OST file corruption?

OST files can be corrupted due to several reasons such as abrupt termination of the Outlook application, power outages, virus or malware attacks, faulty networking devices, synchronization issues, and hard drive failures.

Can I repair OST files from Outlook 2016 and 2019?

Yes, you can repair OST files from Outlook 2016 and 2019. The methods mentioned in this post, both manual and third-party software like the SysCurve Outlook OST Repair tool, apply to all versions of Outlook, including 2016 and 2019.

Is it possible to convert a repaired OST file to different formats?

Yes, with the help of the SysCurve OST Repair tool, you can convert the repaired OST file into different formats like PST, EML, MBOX, HTML, and RTF.

Is it safe to use a third-party OST to PST Converter tool?

Yes, it is safe to use a reliable third-party Outlook OST Repair tool. It is recommended to choose a trusted and well-reviewed software like SysCurve OST to PST Converter. This tool ensures the safety and security of your data while repairing and converting the OST file.

What if the manual method to repair OST file does not work?

If the manual method does not work or if it seems too complicated, you can use third-party Outlook OST repair tools like SysCurve OST to PST Converter. It provides a simpler and more user-friendly way to repair and convert OST files. It also offers advanced features that may not be available in manual methods.

Is there a size limit for the OST file to be repaired?

Most manual methods may have limitations when dealing with larger OST files. However, third-party software like the SysCurve OST Repair tool can handle OST files of any size, making it a preferred choice when dealing with large OST files.

How often should I back up my OST file?

Regular backups of your OST file can prevent data loss. It's wise to back up every time significant changes are made or at regular intervals, such as weekly or monthly.

Can OST files become oversized, and how does it affect performance?

Large OST files can slow down Outlook's performance. It's advisable to regularly archive old items and maintain a manageable OST file size.

What are the signs that my OST file is corrupted?

Common signs of OST file corruption include errors when opening Outlook, inability to synchronize with the Exchange server, missing emails, or frequent Outlook crashes.

Are there any best practices for preventing OST file corruption?

To prevent OST file corruption, regularly update Outlook, avoid abrupt shutdowns of the application, maintain a stable network connection, and keep antivirus software updated.

How do I know which method to use for repairing my OST file?

The choice of method depends on the severity of corruption and the version of Outlook you're using. Begin with simpler methods like using the Inbox Repair Tool, and if that doesn't work, proceed to more advanced methods like third-party Outlook OST Repair tools.

The Final Word

As we've demonstrated, dealing with corrupted OST files need not be a nightmare. With the help of built-in tools like Scanpst.exe and third-party solutions like the SysCurve Outlook OST Repair tool, you can effectively repair and recover your OST files. As with all things technical, caution is advised. Always ensure to back up your files and data regularly to prevent irreversible data loss. We hope this comprehensive guide was helpful in your quest to repair OST files and made the process less daunting.

The Author

Deepak Singh Bisht

Deepak Singh Bisht

Content Lead |

Deepak Singh Bisht is a dedicated IT professional with over 9 years of experience, is a key member at SysCurve Software for the last 5 years. His expertise lies in email migration and data recovery, with a focus on technologies like MS Outlook and Office 365. Deepak, who also delves into front-end technology and software development, holds a Bachelor's degree in Computer Applications.

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