The Free OST converter tool can easily conversion OST to PST file. There is also a demo version available for free which allows to export 30 emails for free convert emails from ost to pst. Along with all MS Outlook users can try this software which is the great tool to transfer the inaccessible Outlook OST file as well as convert the offline OST file into PST, Office 365, Live Exchange Server, EML, MSG, MBOX, vCal, vCard, and EMLX file formats within few minutes. 
outlook ost to pst conversion tool