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4 Methods to Fix errors have been detected in .ost file

Email | 4 min read| Brayden Mitchell | Updated On - November 19, 2022

OST file is the core of your Outlook as it saves all the work which has been done offline. Once the connection with Exchange Server is established, OST file gets synchronized automatically and all the work is updated. Any corruption to such vital file could result in various problems when you work on Outlook. When you try to open or synchronize an offline folder OST file which is corrupted or damaged the following error message is generated:

“Unable to expand the folder. The set of folders could not be opened. Errors could have been detected in ost file. Quit all mail-enabled applications, and then use the Inbox Repair Tool.”

Reasons for Error

‘Unable to expand the folder’ error could be faced by the user due to several reasons. Some of the well-known reasons are:

  1. Sudden system shutdown while Exchange Server synchronization is in progress
  2. Issue with network connectivity while OST file migration remains in progress
  3. File corruption
  4. Exchange mailbox is deleted
  5. Malware Issues in the system


Once the reasons of manifestation of such error are known, the user can fix the issue with any of the following solutions:

  1. Restoration of Outlook files from Backup: The Outlook files get corrupt due to several reasons. However, in every attempt the user tries to recover the OST files in such a manner that the content remains unaffected. To retain the Outlook file, the first and the simplest method is to restore the Outlook file from the back-up.
  2. Run ‘Inbox Repair Utility’: Microsoft offers inbuilt utility to fix the issues with corrupt OST and PST files. To fix the corrupt OST files, it is advised to run the ScanOST.exe (C:\Program Files\Microsoft Office\Office 12 folder) which an element of ‘Inbox Repair Utility’. However, the severe issues with the files cannot be dealt with the inbuilt utility. Therefore, external assistance is required in such case. This inbuilt application service is available for older Outlook versions only.
  3. Clearing existing OST data and recreating OST data: The user can clear the offline OST data using following steps:
    1. Locate OST file. The default location is C:\Users\Sysinfo\AppData\Local\Microsoft\Outlook
    2. Right click on the OST file followed by clicking ‘Properties’
    3. In dialog box, choose ‘Clear Offline Items’ option
    4. Click Ok
    5. Re-launch Outlook
    6. Click ‘Send/Receive’ tab from Outlook 2010. Now, click ‘Update folder’ tab to synchronize the folder form Exchange Server
    7. Delete the previous copy of the Outlook file from the default location or from Account Settings, open the Exchange OST file location using Open File Location option under the Data Files tab.
    8. Restart the Outlook application in configuration with the Exchange account for automatic creation of the updated OST file.
  4. Creating new Outlook profile: Due to corruption in Outlook profile, sometimes the concerned OST files don’t get open. In such case it is recommended to create new Outlook profile by following steps:
    1. Open ‘Control Panel’ and search ‘Mail’. Click ‘Show Profiles’
      Open 'Control Panel' and search 'Mail'
    2. Click Add
      Click Add
    3. Populate the Name field in Profile
    4. Activate ‘Auto Account Setup’
      Activate 'Auto Account Setup'
    5. Once the account setup is complete, click ‘Manually configure account settings’ to resume the ports and server authentication
    6. After the account information is entered, press Test Account button. Upon failing re-try the above steps
    7. Click ‘Next’ and exit wizard followed by ‘More Settings’
    8. Enter the required details
    9. Outlook profile is successfully created. The user can close the dialog box

So, you can try the above solutions for fixing the OST file errors in MS Outlook but if the corruption or issue is severe or you need to take a backup of the OST file to a portable PST file, you can try the OST to PST Converter tool to directly convert offline OST files to PST files with selective data migration. Take a trial with the free demo version of the tool.

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