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Offline Exchange Mailboxes – Corruption and Recovery

Using an Exchange mailbox in offline mode is another useful feature of MS Outlook. Basically, when an Outlook user is not connected with the Server, MS Outlook creates an Offline Storage Table (OST) file on his/her local hard drive. This OST file contains entire data of that user’s mailbox, and thus facilitates him/her to access Exchange Outlook mailbox even when there is no connectivity with the Server.

Moreover, a user can draft emails, add contacts in contact list, and do all the other things in this OST file as he/she does on the original Exchange mailbox, but these changes are updated on the actual mailbox only when he/she is connected back to the Server. The point to be noted here is; the OST file can never interact directly with the Exchange Server or Exchange mailbox. Therefore, to update the changes, it has to convert itself to easily installable Outlook PST file.

However, sometimes it is seen that the OST file fails to convert itself to PST when connected to the Server to sync changes. This occurs either due to the improper Internet connection or due to corruption of your OST file. If the issue is related to Internet connectivity, then you can easily sort it out by checking the connections. But, if the issue is caused as your OST file is corrupt, then the situation becomes troublesome.

Your OST file gets corrupt due to any of the below mentioned reasons:

  • Sudden power failure while you are accessing OST file or synching it with the Server corrupts it.
  • If your internal hard drive is having bad sectors and your OST file happens to be stored on it, then OST file becomes inaccessible or gets corrupt.
  • Improper termination of Outlook while OST is being accessed or when it is updating the changes also corrupts it.
  • Problem with the Internet connection also corrupts the OST file.
  • Sometimes, virus infected storage media corrupts the Exchange OST file.
  • Oversized OST is another cause that corrupts your OST file.

Since a corrupt OST file does not get synchronized with the Exchange Server, it causes inaccessibility of entire Exchange Outlook mailbox data. Generally the corruption of OST file renders an error message or shows some strange behaviors. Some common OST corruption error messages and general symptoms of corrupt OST are:

  • Unable to expand the folder. The set of folders could not be opened. Errors could have been detected in the file xyz.ost. Quit all mail-enabled applications, and then use the Inbox Repair Tool.”
  • Cannot open your default email folders. The file xyz.ost is not an offline folder file.”
  • Errors with number strings like 0x80040116 or 0x8004060c”
  • Outlook recommends you to reduce the size of your OST file.

Mentioned above are common symptoms and errors; however, you can get some other error messages as well, but their resultant is the same and that is inaccessibility of your Outlook mailbox data. However, Outlook facilitates an inbuilt utility in the form of executable file i.e. ‘scanost.exe’ to rectify the corruption issues of OST file, but if the corruption is severe, then this tool too becomes unable to do any needful.

In such situations, using a professional OST to PST converter software is recommended. Professional OST to PST converter software repairs corrupt OST file and converts it to usable PST irrespective of the reason and level of OST corruption. Therefore, by using a reliable converter software for OST, you can repair its corruption and easily synchronize the changes to Exchange mailbox as it converts it to PST itself.

Written By

I am Data Recovery Expert from Stellar Information System Ltd and currently doing research on Outlook PST Recovery Software, Outlook Express Recovery, Exchange Recovery.



  1. Jon Stewart

    February 7, 2013 at 5:35 am

    Open ( ) website easily knows about corruption and recovery of Exchange Mailboxes.

  2. harshi

    February 7, 2013 at 6:43 am

    my mail box has many times got curropted also with no recovery i guess i would have found this before as i have lost all my mails ! :(:(

  3. Maria

    February 11, 2013 at 6:19 am

    For converting corrupted or damaged OST files to PST files so that you can access them with Outlook download a good OST to PST converter tool.

  4. Chirag Arora

    February 11, 2013 at 9:14 am

    Yes, I agree with @Maria. You can easily repair your damaged an OST file & convert OST file into PST file format using third part stellar phoenix ost to pst converter. download demo version from here

  5. RichardJenson

    February 15, 2013 at 8:03 am


    As your OST file is corrupt then by using a utility tool named Lepide Exchange Recovery Manager you will be able to quickly repair and recover in your corrupt OST. Besides this it can also convert the OST to PST so that you can able to view in your PST without the exchange account


  6. Tom

    February 18, 2013 at 7:48 pm

    This seems like a useful tool in the event that you lose access to your exchange server. Converting the OST’s to PST will allow you to restore the emails. If you still have access to the Exchange server you can create a new email profile and the OST file will be automaticly recreated by downloading the mailbox from the exchange server.

  7. Adin Abel

    April 8, 2013 at 9:56 am

    To resolve Exchange server corruption issue we really we need tool through which we can recover our lost database and if these things possible without investing anything is possible then then user get more happy so go on this link and recover entire database of Exchange server at free:- exchangerecoverysoftware .org/microsoft-exchange-server-recovery.html

  8. Sally

    June 17, 2013 at 5:13 am

    I don’t think I am going to be working offline, if there is a risk of losing data.

  9. jonsenbillie

    August 19, 2013 at 11:03 am

    An Exchange recovery tool is the best solution to search, migrate and Exchange Migration tool. Exchange mailbox recovery software repairs and
    recovers, corrupt, edb file and offline edb files and extract complete single or multiple mailboxes to pst.

  10. Keith Larry

    August 28, 2014 at 2:40 am

    Here is a best tool that worked for me to repair and restore corrupt OST file as PST file

  11. Alina jonson

    September 16, 2014 at 12:02 pm

    Recover corrupt OST file and convert them PSt file format, use Kernel for OST to PST Conversion Software to recover .ost file and convert them .pst file format. This is very advanced tool to recover all corruption issue from ms outlook and save them new PST file.

  12. samfredi

    November 22, 2014 at 8:49 am

    Recover offline EDB file with PDS Exchange recovery software. With this tool users can effortlessly repair corrupt EDB files and can easily recover entire data from Exchange mailbox in readable mode.

  13. Stwain

    November 22, 2014 at 9:01 am

    So many factors can be liable to corrupt EDB files but to recover tat kinds unresponsive Exchange EDB files make use of this effective Exchange EDB file recovery software. It makes EDB data readable by recovery of inaccessible EDB files against any situation of Exchange corruption. Microsoft EDB converter program operates with excellence over unreadable EDB files and successfully open Exchange data in PST file format in satisfactory manner.

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