As I have mentioned earlier, import OST files into Live Exchange is very important in order to facilitate the movement and or access the data in offline mode. This is because the OST files cannot simply be imported directly inside an Exchange. They have to be first transformed into PST files which are recognized by Outlook for the purpose of importing them. Transfers made using this conversion ensure that the emails and contacts as well as all other mailbox items are moved intact.
Manual Method:
Open Outlook and navigate to File > Open & Export > Import/Export.
Choose Export to a file, select Outlook Data File (.pst), and follow the prompts to convert the OST to PST.
Finally, import the PST into your Exchange account.
Automatic Method: For a more efficient solution, consider using the WebbyAcad OST Converter tool. This software allows direct conversion of OST files to PST or imports them straight into Live Exchange with just a few clicks, streamlining the process significantly.