Convert OST to PST

Fix OST file error: “Cannot open OST file. You must access Exchange at least once to use the OST file”

Offline storage table (OST file) is one of the important Outlook data files to view, create, delete and manage your mailbox items even in offline mode. For this MS Outlook is connected with a server-side application like Exchange Server to ensure smooth synchronization of data between the offline folders and the server. Any changes made in the OST files get automatically synchronized with Exchange Server when the internet connectivity is back.

But in some unfavorable conditions such as accidental deletion of OST files, downtime issues or networking connection failures, corruption of OST files due to oversizing issues (more than 2GB), virus attacks, abrupt termination of Outlook etc. may disturb the normal synchronization routine. When you try to synchronization the OST files with Server, user is generally displayed an error message like:

“Cannot open OST file. You must access Exchange at least once to use the OST file.”

In this condition, the information stored in OST files turns inaccessible including email messages, contacts, calendars, tasks etc. No matter how many times you try to access the OST files, it will display the same message.

Cause of OST File Error

This error “Cannot open OST file” occurs when MS Outlook application automatically creates new offline storage files for which Exchange Server refuses to identify them. Hence the user is displayed “Cannot open OST file” error message.


Outlook provides an inbuilt tool (scanost.exe) to verify the integrity of synchronized offline storage table files manually. For this, the user is suggested to delete the OST file and MS Outlook application need to re-download the information from the Exchange Server.

Once the data is fully downloaded from the server, then you can import the PST files to new OST files. For this follow the mentioned steps accurately:

  1. Go to the File tab and then go to ‘Open’ option, and then select ‘Import’ option to import files into Outlook.
  2. From the Import & export wizard window, choose ‘Import from another program or file’ option and click Next button.
  3. Choose Outlook data file (.pst), and click Next button to proceed further.
  4. Click on Browse, and then provide the location in of the PST file that you want to export.
  5. From the available options, choose ‘Do not import duplicates’ option and then click ‘Next’ button.
  6. In Select destination folder, select a folder to that you wish to import the information. Click Next.
  7. Now click Finish.

Although scanost.exe is not available in the latest versions of Outlook, but you can still use inbox repair utility (scanpst.exe) to check the integrity. This utility is helpful to check and repair internal data structures of OST files that are causing synchronization issues.

However, this manual method is time-consuming and uncertain about the success of recovering OST files with complete accuracy. In this situation, users can try a robust alternative, i.e. use third party OST to PST software to get rid of this troubling issue of “Cannot open OST file. You must access Exchange at least once to use the OST file.” Within a matter of minutes.

The OST to PST is a powerful OST file recovery software that can even recover permanently deleted OST files within a matter of minutes. Users can easily migrate the OST files to Outlook PST files while preserving complete data integrity. Using this Convert OST to PST Free tool you can even export the recovered files to Office 365 platform, web-based email clients or to any email servers.

Word of Caution

In order to avoid OST file corruption issues, user is recommended to keep a regular back of updated offline storage table files and ensure to have strong internet connectivity while synchronizing OST with Exchange. Additionally, you can make sure that you have installed antivirus software on your system to avoid the data threat circumstances. Get more detail, Visit here:-

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