Are you looking for the best OST to PST Converter then I would advice you to use professional's recommended ZOOK OST to PST Converter tool. It is specialized program to convert unlimited OST data files to PST format including emails, contacts, calendars, notes, attachments, journals, etc. This is capable to convert big sized OST file into multiple PST files. It is fully supportable to all versions of Microsoft Outlook and Windows Operating Systems.