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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.



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