If you really want to open OST files without exchange server, you can try eSoftTools OST to PST Converter Software. This software has an email filtration option it restores OST emails on specified dates by date range. It recovers an OST file that is created from IMAP, Office 365, Exchange Server, and Outlook.com. This software will give you 24/7 technical support. Also, you can try a free demo version of this tool which converts 25 items from every folder of the OST mailbox.
About Know More: Open OST files without exchange server
