Fix the Error “Cannot open your default email folders. The file xxxx.ost is not an offline folder file.”

When you use Microsoft Outlook, your email and all mailbox items are saved in .ost and .pst data files. The Offline data file (OST) file stores essential information of the MS Outlook mailbox. It holds a replica of Exchange mailbox items on the local system and allows you to work offline or when the server experiences downtime. When the connection is re-established, all the mailbox content is synchronized smoothly with Exchange Server. Sometimes when the corruption enters the OST files or any anomaly disturbs the synchronization process, then the following error appears.

“Cannot open your default email folders. The file XXXX. ost is not an offline folder file.”

Where ‘username. ost’ indicates the OST file created automatically by MS Outlook when it is working with the Exchange mailbox offline. The MS Outlook OST file becomes inaccessible in a way that even MS Outlook cannot recognize or sync with them. It restricts users from accessing the OST data file and halts the overall working. This error affects the mailbox and can also lead to data loss if not operated properly.

Reason for this MS Outlook Offline OST Error

The OST file errors are common and there could be many possible reasons which causes it. Here is the list of all possible reasons that leads to OST file inaccessibility error:

  • Virus attack in Microsoft Outlook application.
  • An unstable internet connection or any network connectivity issue between the Server and MS Outlook can also lead to file inaccessibility.
  • Any corruption in the OST file restricts the user from accessing the file.
  • When the OST file unable to synchronize properly with the Exchange server mailbox.
  • Due to communication problems between Microsoft Outlook and the Exchange server.
  • When the Exchange server unable to access the particular mailbox or when deleted accidentally.
  • Also, Hardware and software issues can be the reason too.

How to Manually Rectify the OST File Corruption Issues?

Solution 1:

Locate OST file and check its information- To resolve the issue search for that particular OST file that is creating trouble.

  1. Locate the OST file which is causing the error.
  2. Ensure that the user profile information is correct in MS Outlook and Exchange Server.
  3. Ensure the availability of a proper internet connection.
  4. If Outlook is working properly, then try to rename the corrupted OST file with a new name and re-open it in MS Outlook.

Solution 2:

Delete and Recreate new profile – Change your email address and create the new MS Outlook profile and then open the MS Outlook data file in a new account.

Follow the steps given below:

  1. Firstly, open Control Panel > All Control Panel items.
  2. Now, Click on Mail button.

3. Then click on the “Show Profiles” option.

4. Then choose the associate Profile that needs to be removed.

5. Select the “Remove” option to delete the opted profile.

6. After that choose the “Add” button to create a new profile.

7. Now fill in the new profile details and then select “OK“.

8. At last, launch the Outlook profile and try to open the OST file again, and check whether the issue has been resolved.

Note: Before implementing this method always keep a backup for your mailbox data files so that even if the file is corrupted you will have the backup for restoring.

An Alternate Solution:

Repair the OST file and extract all data from it- One of the best ways to fix this Outlook OST file issue is to repair that particular OST file and extract all its data. MS Outlook has inbuilt tools to Repair OST files i.e.; the Inbox Repair tool SCANOST. EXE. This tool checks the MS Outlook data files and corrects if any error is found. But before you do, you need to be 100% sure about the process and know how to migrate your data safely so you don’t make any mistakes. The easiest and safest way to repair an OST file is by converting it into PST format with the help of an OST to PST converter.


If all of the above-said methods do not work out to solve the “The file XXXX.ost is not an offline folder file” OST file issue. Also if you don’t have a backup of that OST file at hand, then you can use the appropriate OST to PST Converter to resolve it and restore the inaccessible OST data.

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