What is OST File?OST abbreviated as Offline Storage Table and it is an offline folder file in MS Outlook. In case, if Outlook application disconnects from the MS Exchange server, then the Offline folder file (OST) allows you to sustain the work in Microsoft Outlook. Users can send new mails, read or remove existing emails, etc. Once the connection is reestablished, whatever alteration you have done to the OST file in offline mode gets automatically synchronized with its mailbox on Exchange server.
Offline Storage Table (OST) is a duplicate copy of mailbox lying on MS Exchange Server and stored in the hard drive of your machine. In case, if Microsoft Exchange server gets damage then it will not affect to OST file which is save in HDD.
But sometimes you may get error while accessing your OST file in Microsoft Outlook. Sometimes you might also observe that few of your items are either removed or missing from OST file. It generally happens because of human mistakes or Offline Storage Table (.ost) file corruption.
Therefore, if there is a doubt that Outlook offline data file (.ost) is corrupt, then you need to run OST Integrity Check tool (Scanost.exe) to resolve the corruption.
Reasons for Corruption of OST FileThere are various reasons for the Outlook OST file to be corrupted, and the reason may be related to software and hardware malfunctions. The corruption cases have been classified in two categories, i.e. hardware and software reasons.
- Crashed Data Storage Device: If the Offline folder file (.ost) is saved in your Hard Disk and the data storage sector on the HDD becomes bad, then the OST file may be corrupted or damaged.
- Problem in networking device: As we know that the OST files are synchronized with the Exchange Server through a network connection. If cables, routers, hubs or any other devices results in the failure of network, then the synchronization process fails, damaging or corrupting the OST files.
- Power Failure Issue: If a power failure occurs when you are accessing or synchronizing the Exchange Server OST files, then in most of the cases OST files gets corrupt.
- Incorrect File System Recovery: A file system recovery can also cause Outlook OST file corruption when file system is broken and a data recovery tool is used to recover the OST files.
- Virus and Other Malicious Software: Viruses or Infected Trojans may get corrupt or damage the Outlook OST files or make them inaccessible.
- Synchronization Error: The synchronization failure between the offline folders and the Server may also lead to errors leaving the OST file corrupt.
- Abnormal Microsoft Outlook Termination: You should follow the proper steps to quit from Microsoft Outlook. To do so, you should save all the changes made in the OST file before closing the Microsoft Outlook. However, if MS Outlook shut down abnormally then this may interrupt the functioning leading to corruption.
Effects of OST File CorruptionsIf any of the above-mentioned issues cause the OST file on your system to be corrupted, the MS Outlook profile and Exchange account associated with that OST file will become inaccessible. If you try accessing it, the follow errors may surface:
Cannot open your default email folders. The file C:\Users\.......\outlook.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.”
“Confront a large numbers of conflict items”
Cannot open particular Outlook items when offline.
Various errors when synchronizing Exchange Server mailbox with your OST file.
Repair OST File in Microsoft Outlook 2007 & Its Limitations:In Microsoft Outlook 2007, you can repair your OST file by following the below steps:
Path to Find SCANOST Tool:
32-bit Windows C:\Program Files\Microsoft Office\Office12
64-bit Windows C:\Program Files (x86)\Microsoft Office\Office12
After finding the executable file for SCANOST.EXE, run it and perform all the steps.
UPDATE: Unfortunately, the Microsoft Outlook OST Integrity checker software (SCANOST.EXE) is not installed with Microsoft Outlook 2010, 2013, and 2016. So, this can be the limitation of this utility. But there is always a way to sort any issue. Let see that in the next section.
How to Repair OST File When They Are Corrupted in Outlook 2010, 2013, And 2016?As we discussed above that Scanost.exe utility is used in earlier versions of Microsoft Outlook to verify the integrity of synchronized data. You can still run the Inbox Repair Tool (Scanpst.exe) on an offline Outlook Data File (.ost) to check and repair the internal data structures, as they are similar for both data files of Outlook.
Know the location and how to run Inbox Repair Tool: https://support.microsoft.com/en-us/kb/272227
If the issue persists, then the Outlook data file might be highly corrupted or damaged. Inbox Repair Tool (SCANPST.EXE) does repair only the header section of the file. So, in that case you have to go for a third party OST Recovery Tool so that you can easily recover highly corrupted OST File & fix kinds of issues.