There are many reasons that will make your Exchange offline folder (.ost) file corrupted or damaged. 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 OST files, the OST files will likely get corrupted. There are mainly three types:

  • Data Storage Device Failure. For example, if your hard disk has some bad sectors and your Exchange OST file is stored on these sectors. Then maybe you can only read part of the OST file. Or the data you read are incorrect and full of errors.
  • Networking Connection Failure . When you synchronize the OST file with the server through a network connection, if the network interface cards, cables, routers, hubs and any other devices constituting the network connection have problems, then the synchronization process will be aborted and the OST file is likely to get corrupted.
  • Power Failure. If a power failure happens when you are accessing or synchronizing the OST files, that may leave your OST files damaged.

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

Software Reasons:

Also many Exchange OST file corruptions occur due to software related issues.

  • Incorrect File System Recovery. You may find it is unbelievable that a file system recovery may cause OST file corruptions. But in fact, sometimes when your file system is broken, and you try to hire a data recovery tool or expert to recover the OST files on it, the files recovered may still be corrupt, because:
    • Due to the file system disaster, some parts of the original OST file are lost permanently, or overwritten by garbage data, which makes the final salvaged OST file incomplete or contain incorrect data.
    • The recovery tool or expert doesn’t have enough expertise that it/he may collect some garbage data and save them as a file with .OST extension. As these so-called .OST files don’t contain any valid data of the Exchange offline folder files, they are totally useless.
    • The recovery tool or expert has collected the correct data blocks for the OST file, but has not combined them in a correct order, which also makes the final salvaged OST file unusable.

    Therefore, when a file system disaster occurs, you should find a good data recovery tool/expert to recover your OST files. A bad tool/expert will make the situation worse instead of better.

  • Virus or Other Malicious Software. Many viruses will infect and damage the Exchange OST files or make them inaccessible. It is highly recommended to install quality anti-virus software for your Outlook and Exchange email system.
  • Terminate Outlook Abnormally. In normal situation, you should quit Outlook gracefully by saving all your changes to the OST file and then clicking “Exit” or “Close” menu item. However, if Outlook is shut down abnormally when you are opening, accessing or synchronizing the OST file, then the OST file is prone to be corrupted or damaged. This can happen if power failure mentioned above occurs, or if Outlook is busying in doing something and you terminate it by click “End Task” in Windows Task Manager, or if you turn off the computer without quitting Outlook and Windows normally.
  • Synchronization Error. The synchronization between the offline folders and the server may also lead to many errors, including large numbers of conflict items, cannot open particular Outlook items, etc.
  • Deficiencies in Outlook programs. Every program has deficiencies, so does Outlook. Some deficiencies come from the short sights of the designers. They can usually be expected but cannot be solved simply by fixes or patches. For example, in the early days, the Microsoft designers don’t believe there will be bulk of data in OST files, so the maximum size of OST file that can be processed by Outlook 97 to 2002 is 2GB by design. But nowadays, the communications and personal information grow so quickly that the OST file increases dramatically. When the OST file approaches or goes beyond 2GB, it will get corrupted. While the other deficiencies result from the carelessness of the programmers. In general, they cannot be expected but once found, can be solved by small fixes or patches. For example, when Outlook encounters an unexpected error, it will say “Microsoft Outlook has encountered a problem and needs to close. We are sorry for the inconvenience.” and terminate abnormally, which is very likely to make the OST file corrupted.

Symptoms of Corrupt OST Files:

For your reference, we have collected a list of common errors and problems in Exchange OST file, which includes the symptoms and detailed explanation when a OST file gets corrupted.

Fix Corrupt OST Files:

You can use our award-winning product DataNumen Exchange Recovery to recover your corrupt Exchange OST files.