If you need to convert OST to PST without Outlook. I recommend to you the best third-party solution eSoftTools OST to PST Converter tool. It can save your OST data file into multiple file formats. This tool exports single as well as multiple files instantly in PST format without an Exchange server. It’s 100% tested from anti-virus and online scanners. It can Support ANSI and Unicode format. This tool is based on a GUI Operating system. A preview option is available to show the conversion after the conversion user can easily manage internal data using the email filter option and save OST files into PST, EML, EML, MBOX, HTML, MSG Office 365.