Do you want to open OST file in outlook 365, then I suggest you to get SysInspire OST to PST converter software. This tool can open OST file in Outlook 365 by using this tool users can convert OST file into multiple file format such as OST to PST, EML, EMLX, office 365, HTML, Yahoo Mail, etc. It has a demo version that can allow users to convert 25 items from each folders. It has a preview option users can preview OST file before conversion. It can support all versions of Windows OS. This tool does not require to install MS Outlook to open OST file in users Pcs.