Offline Storage table or OST is a file format to store Exchange mailbox information when MS Outlook fails to establish connection with Exchange Server. OST file synchronizes with MS Exchange Server soon after Outlook is reconnected with Exchange network. But presence of several factors in the MS Exchange environment halts OST synchronization process. These factors are mentioned below :

  • Virus, spyware and adware codes
  • Unexpected system shutdown
  • Exchange Server crash
  • Internet disruption for long time
  • Abnormal OST file size
  • Computer hardware malfunctioning
  • Corrupt or missing Windows system file
  • Several Outlook profiles on client Server

OST Synchronization errors

  OST corruption or synchronization failure is highly undesirable event in large IT organizations who use MS Outlook client for email communication. One of the common OST synchronization errors is shown below:

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

Here pqr.OST represents an Exchange OST file that shows abovementioned error message.

Recommended Solution
Use Recoveryfix for OST to PST Converter to fix error ‘Unable to Expand folder’ and other issues related to an OST file.


You should check whether there are multiple Outlook profiles for a single account and delete all profiles from your system.  Then you can recreate a new Outlook profile using following steps:

  1. Click Windows start menu
  2. Go to Control Panel>Mail
  3. Hit “Show profiles” in the new Windows
  4. Press “Remove” button to delete old Outlook profiles
  5. Click “Add” to create a new Outlook profile and press “Ok” button
  6. Click “Manually configure Server Settings or additional Server types”  in the new Windows and press” Next
  7. Add your Exchange account address and press “Next
  8. Click “Finish” to  complete creation of Outlook profile
  9. Restart MS Outlook to  synchronize with Exchange Server

If the above mentioned option does not cure OST synchronization error then it may be generated due to hardware failure or other reasons. Microsoft Outlook is provided with inbuilt tools scanost.exe and scanpst.exe to cure database corruption. Scanost tool is also known as OST integrity checker and fixes many OST synchronization errors. OST integrity checker tool is stored in local MS Office folder of a Windows Server. You’ll not find scanost.exe in the system that uses Outlook 2010 or Outlook 2013. Default location of scanost.exe is:

C:\Program files\Microsoft Office\ Office 12\scanost.exe

Now start repairing corrupt OST file using following steps:

  • Close MS Outlook if it is running
  • Double click on Scanost.exe program
  • Select Outlook profile from your system that is linked with your Exchange account
  • Click “Connect” if  options “Connect” or “Offline” appear on your computer screen
  • Select “Scan all folders” option and also check “Repair errors” check box
  • Click “Begin Scan”  to start repairing selected OST file
  • Close scanost program

However, OST corruption due to Exchange Server crash, hardware malfunctions or other factors cannot be fixed by scanost tool or other manual options. In such circumstances, you will have to use an automatic OST to PST Converter tool to fix OST errors.

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RecoveryFix for OST is an ideal solution to all OST corruption issues. It recovers whole Exchange mailbox from a corrupt OST file and stores recovered mailbox information in the PST file.  This OST repair tool can also restore deleted Exchange accounts of a Server. It successfully recovers mailbox data even from password protected, compressed and highly encrypted OST files.


OST synchronization errors are generated due to various factors such as virus attacks, hardware malfunctioning and others. There are various manual options to fix OST corruption such as creation of new Outlook profile and OST integrity check tool. However, manual recovery of OST files is not successful in many cases. You must choose automatic OST Repair tool to fix critical OST corruption issues.