Open an OST file in Outlook in simple steps using eSoftTools OST to PST Converter, which I've used myself and found excellent results. Furthermore, the tool's features are very beneficial. Using this software, you can convert any OST file to any email cloud, such as OST to Gmail, OST to Yahoo Mail, or OST to Office 365. This software has been human-tested, so there's no data loss. Using this software, you can convert up to 25 emails from OST files to PST for free.