How to repair the damaged Offline Folder (OST) files and access data from them?

OST (Offline Storage Table) is an offline folder file that holds data of Outlook profile when you are in the offline mode. These files keep a copy of emails and other attributes of Outlook from Exchange Server. While synchronizing an .OST file in MS Outlook with your mailbox on the Exchange Server, you might face few error messages such as:

  • “Cannot open your default email folders. The file xxxx.ost is not an offline folder file.”
  • “Unable to expand the folder. The set of folders could not be opened. Errors could have been detected in the file xxxx.ost. Quit all mail-enabled applications, and then use the Inbox Repair Tool.”
  • “Encounter a large numbers of conflict items”
  • “Cannot open particular Outlook items when offline”
  •  “OST file cannot be accessed in Outlook”
The occurrence of any of the above-mentioned error message simply indicates that the stored OST file has gone corrupt or damaged. There may be numerous reasons responsible for the corruption of these .OST files and are categorized as:
  • Hardware Reasons: Data storage device failure, networking connection failure, power failure
  • Software Reasons: Incorrect file system recovery, virus or other malicious attacks, abnormal termination of MS Outlook, synchronization error, deficiencies in Outlook programs.

On corruption of OST files, they need to be repaired to recover the entire email data with complete accuracy. Microsoft Outlook itself provides an inbuilt OST Integrity Checker (Scanost.exe) that helps in identifying and repairing the OST file synchronization issues. This tool scans both damaged OST file and the mailbox on the Exchange Server, compares the email items and folders in both, and resolves the synchronization issues.

This inbuilt tool does not alter the mailbox on the Exchange Server but records the differences in the scan log that can be resolved. The scan log also identifies the situations that the tool could not resolve and needs to be fixed manually. Note that, to use the OST Integrity Checker, you must be connected to your Exchange account so that the tool can scan your mailbox folders and items.

Another inbuilt tool for OST file recovery is the Inbox Repair tool (Scanpst.exe) that scans the .OST files and analyzes the file structure integrity. This tool also helps in diagnosing and repairing the errors in Exchange OST files. The tool scans the .OST files and ensures that the file structure remains intact. Moreover, the tool does not interact with the Inbox folder on the Exchange Server in any means.

In case both these OST Integrity Checker (Scanost.exe) and Inbox Repair tool (Scanpst.exe) fails to repair the damaged, corrupt or inaccessible OST files, then you must use a third-party tool like OST to PST. This third-party solution accurately repairs the damaged OST files, recovers the entire email data and stores them in PST files. On performing conversion from OST to PST, the entire email items can be accessed with Microsoft Outlook. This tool works well with Windows 8 and Windows 10 OS platforms. Available in two different licenses – Corporate and Technician , it can be downloaded for free as trial version to evaluate its capabilities.