OST File Synchronization Error


Resolve “Unable to Expand….” OST file Synchronization Error

Offline Storage Table (OST) file may get corrupted due to various reasons such as Microsoft Exchange Server’s downtime, Exchange Server crash, accidental user account deletion, Exchange Server database corruption, virus attacks, data storage device failure, networking connection failure, abnormal Outlook termination, synchronization error, deficiencies in Outlook programs, unexpected system shutdown, power failure, etc. While using MS Outlook for opening corrupt, damaged or inaccessible OST files or synchronizing an OST file, an error messages given below may be generated:


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

Here, ‘xxxx.ost’ is the implicitly created offline folder (OST) file created by MS Outlook while working with Exchange mailbox offline.

In order to resolve this error and prevent data loss, follow the steps given below:
  • Close Microsoft Outlook and any other applications that may access the OST file.
  • Find the OST file causing the error: User can easily find the corrupt OST file using the information provided in the error message. User can also use the Search option provided by Windows for searching the OST file.
  • Recover the offline data in the OST file: Use Advanced Exchange Recovery for scanning the OST file, recovering the data in it and saving them in an MS Outlook PST file for accessing offline data including all the mail messages and all other items in Exchange mailbox using MS Outlook easily and efficiently.
  • Backup the original OST file: Take backup of original OST files as per purpose of data security.
  • Rename or delete the original OST file that causes the problem.
  • Import the data recovered in Step 3: After resolving the OST file problem, keep the new OST file for Exchange mailbox open and then open the PST file generated in Step 3 with MS Outlook. As it contains all recovered data in original OST file, user can copy required items to new OST file selectively.
  • Fix the error: Check the email account settings in MS Outlook and ensure that Outlook can connect to Exchange Server correctly. Restart Outlook and send/receive emails on Exchange mailbox which creates a new OST file automatically and synchronize its data with the Exchange mailbox.
In case the above given method does not work, then the mail profile becomes incorrect, delete that and create a new one as given below:

6.1 Close MS Outlook.

6.2 Click Start, and then click Control Panel.

6.3 Click Switch to Classic View if user is using Windows XP or higher versions.

6.4 Double-click Mail.

6.5 In the Mail Setup dialog box, click Show Profiles.

6.6 Select one of the incorrect profile in the list and click Remove in order to remove it.

6.7 Repeat the above step until all incorrect profiles have been removed.

6.8 Click Add to create a new profile and add email accounts according to their settings on the server.

6.9 Start Outlook and re-synchronize your Exchange mailbox, the problem gets resolved.