If you want to convert OST to PST, you can try any professional software like OST to PST Converter. This software easily converts OST to PST and different file formats like Zimbra, Gmail, EML, EMLX, vCard, ICS, MSG, Office 365, Live Exchange server, MBOX and etc. The software maintains OST elements such as emails, notes, tasks, contacts, calendars, etc. The application also convert OST file to the Office 365 and Exchange Server account.