you can Download ost to pst converter software to convert bulk OST to PST Outlook format. The outlook ost converter software permits consumer to transfer the email messages and data items of offline OST emails, mails in Outlook. It free unlimited ost to pst converter application provides the whole import OST files into PST format by maintaining the data honesty and email attributes. At the end, users will get their complete emails at same folders and sub-folders without altering any information.
More info- convert ost to pst manually