I want to suggest the most effective and fastest software MailsDaddy OST to PST Converter to convert OST to PST file. It is the best tool for quick and safe conversion of your OST files into PST. You can export your OST file with multiple export options, such as PST, EML, MSG, HTML, MBOX, RTF, MHTML, CSV/VCF (for contact), and ICS (for calendar). You can also migrate offline OST files into Office 365 and Live Exchange Server. Before purchasing you can try the free trial version with limited functionality, such as converting the first 20 items per folder to evaluate the software.