There will only be one Best free ost to pst converter free tool, which will always have the highest and outstanding functionality to conversion data from ost to pst outlook format. Ost file Converter is a tool that converts ost files into a variety of formats- PST , Office 365 account, pst file, EML, EMLX, MSG, HTML, MHTML, MBOX, VCF, CSV, ICS, Live, Exchange Server, Zimbra, Gmail, Yahoo, and etc.