PST file since Outlook does not allow direct import of OST files. Heres how you can do it:

1. Open Outlook 2013 and ensure the OST file is connected to your account.

2. Create a New PST File:

   • Go to File > Account Settings > Account Settings.

   • Click on Data Files tab and then Add to create a new PST file.

3. Copy OST Items to PST:

   • In Outlook, simply drag and drop your emails, contacts, calendar, etc., from the OST file into the newly created PST file. This will copy all items.

4. Backup and Export:

   • Once everything is copied, you can go to File > Open & Export > Import/Export, and choose Export to a file to save it as a PST file for future use.

5. Use a Third-Party Tool (Optional): If you have trouble with manual conversion, you can use specialized third-party tools like Stellar OST to PST Converter or Kernel for OST to PST to automate the process.

Once you have the PST file, you can open it in Outlook 2013 and access your data. Let me know if you need more details or guidance!