OST (Offline Storage Table) files are used in Microsoft Outlook to store emails, contacts, tasks, and other data locally on a user's computer when they are using a Microsoft Exchange account. PST (Personal Storage Table) files are also used in Microsoft Outlook to store emails, contacts, tasks, and other data, but they are typically stored on the user's computer rather than on a server.

• There are a few different methods that you can use to convert OST to PST format. The first method that you mentioned is to use the export function in Microsoft Outlook to export mailbox data to a PST file. This method is only applicable if you have the OST file for the current Outlook profile that you are using.
• The second method that you mentioned is to enable the Auto Archiving feature in Outlook. This feature allows you to automatically move older items from your mailbox to a PST file on a regular basis. This can be a good way to free up space in your mailbox and keep your email organized.
• The third method that you mentioned is to use the Microsoft OST to PST Converter tool. This is a specialized tool that is designed to convert OST files to PST format. It is recommended by many experts because it can help to ensure high data integrity during the conversion process. You can try the free demo version of this tool to see how it works before deciding whether to purchase the full version.

Overall, there are a few different methods that you can use to convert OST files to PST format. It's important to choose the method that is most appropriate for your needs, taking into account the size of the OST file and the number of files that you need to convert.