The Exchange offline folder (.ost) file is a local and offline copy of the mailbox on the Exchange server. Whenever the mailbox on the server is not available permanently, the OST file is called orphaned.

There are many reasons that will make your Exchange offline folder (.ost) file orphaned. We classify them into two categories, i.e., hardware reasons and software reasons.

Hardware Reasons:

Whenever your hardware fails in storing or transferring the data of your Exchange Server databases (.edb), a data disaster happens and the server will crash. At that time, OST files will get orphaned. There are mainly three types:

  • Data Storage Device Failure. For example, if your hard disk has some bad sectors and your Exchange Server databases are stored on these sectors. Then maybe you can only read part of the database file. Or the data you read are incorrect and full of errors. Such a data corruption will make the database unavailable and your OST file orphaned.
  • Power Failure or Shutdown Server Abnormally. If a power failure happens or you shutdown the Exchange server improperly when the Exchange server is accessing the databases, then that may cause your databases damaged and your OST file orphaned.
  • Controller Card Malfunction or Failure. If a caching controller is used with Exchange Server, its malfunction or failure will cause all the cached data lost and the database corruption, so to make the OST file orphaned.

There are many techniques to prevent or minimize the Exchange Server database corruption and the OST file being orphaned due to hardware problems, for example, UPS can minimize the power failure problems, and using reliable hardware devices can also reduce the chances of data corruption.

Software Reasons:

Also Exchange OST file can be orphaned because of software related issues.

  • Delete, Disable, or Deny Access of the Mailbox on Exchange Server. If the mailbox on the Exchange Server corresponding to the OST file is deleted or disabled by your server administrator, or your access to the mailbox is denies. then your local OST file is orphaned and you must rely on DataNumen Exchange Recovery to retrieve the contents of your mailbox.
  • Virus or Other Malicious Software. Many viruses will infect and damage the Exchange Server databases and make them unusable, which will also make the OST file orphaned. It is highly recommended to install quality anti-virus software for your Exchange Server system.
  • Human Misoperations. Human misoperations, such as deleting databases by mistake, mis-partitioning the storage device, mis-formatting the operating system, will all cause the Exchange Server database unavailable, and so make the OST file orphaned.

Fix Orphaned OST Files:

When your OST files are orphaned, you can still use our award-winning product DataNumen Exchange Recovery to recover the data from your orphaned Exchange OST files, so to retrieve the contents of your mailbox again.