Email is one of the primary methods of communication at workplace today, which is why most of the organizations prefer Outlook email program to maintain robust mailbox integration along with seamless support of offline access. Data files (both OST and PST files) are the backbone of Outlook as they play an inevitable role in performing flawless messaging communication.

Offline storage table is equally important for the Server besides Outlook, to maintain smooth and automatic data synchronization, even when there is instable internet connectivity. Exchange Server uses the OST files to update the changes that the user has made during the offline period and hence keeping your mailbox up-to-date, without losing a bit of information.

However, OST files have been notorious for its frequent corruption issues that may occur because of data synchronization problems, oversizing of files, virus attacks, abrupt system shutdown etc. Here are some of the common reasons due to which an OST file gets corrupt:

  • Oversized OST file – The probability of corruption becomes higher, when an OST file reaches to the default storage limitations, such as 2 GB.
  • Any software upgrade or add-ons incompatibility may also affect the health of the OST files while resulting in data loss.
  • Malware/Virus attacks are also responsible for damaging OST files and hence making data inaccessible for the users.
  • When a data file is deleted accidently using control + shift key, then it cannot be restored from Recycle Bin as well, then you no longer can access OST files in such a case.
  • Frequent data synchronization issues can result in the corruption of OST files

The corruption issue in OST file is often accompanied with an error message such as:

‘Cannot open your default email folders. The file xxxx.ost is not an offline folder file’ 

Consequences of this error message:

When you encounter this error message, then you are restricted to send or receive emails and it may also cause further issues, such as:

  • When data becomes inaccessible, then it may even result in information lapse.
  • Users face restriction from opening mailbox items such as emails, contacts etc.


You can resolve this OST file issue using the below mentioned three methods. However, backing up your data is always a good practice to avoid any futuristic disaster.

Method I: Locate and trace file information

  1. Find the corrupted OST file throwing this error message: ‘the file xxxx.ost is not an offline folder file’.
  2. Make sure that user profile information provided in Outlook and Exchange is correct.
  3. Verify that you are using a reliable internet connection to ensure smooth synchronization between client and the server.
  4.  Rename corrupt OST file with a different name. Now try to open the file in MS Outlook (however if Outlook program is working).

Method II: Diagnose software and hardware consistencies:

If you are unable to open the OST file using the first method, then try to diagnose the hardware/software condition and ensure that they are not conflicting. To do that verify your hardware components like connectors, routers, data cards etc. are working perfectly. However, if you find no such hardware or software glitches then jump to the next method.

Method III: Remove and recreate the existing Outlook Profile

In this method, the existing Outlook profile has been removed and a new profile is being created. Here are the steps to remove and recreate Outlook profile.

  1. Go to “Start” button and open “Control Panel” option.
  2.  Click and open “Mail” settings in “Control Panel” window.
  3. When “Mail Setup” window pops-up, click on “Show Profiles” button

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4. Now, select and click the Outlook profile that has to be deleted from the list of profiles.
5. On the general tab, click “Remove” button to make the changes.

Note: The profile information is also showcased in the empty area under “The following profiles are set up on this computer” as shown in the image

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6. Now, hit on “Add” button to add and create a new Outlook profile.
7. Submit the relevant account information, and click “OK” button.

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8. Lastly, launch the newly-created Outlook profile, and verify if the problem has been resolved.

However, if the problem is not resolved using the above-discussed manual technique then try taking the help of a professional third-party recovery tool. OST to PST converter is a fast and friendly tool to restore the lost and deleted information from corrupt OST files. It even allows to convert OST files to PST, EML and MSG formats in a single attempt.

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