I suggest you download the SysInspire OST to PST converter tool that can help you to change OST files to PST and multiple file formats such as HTML, EML, EMLX, Office 365, etc. It has 10+ file formats for conversion. It has split PST file option in which users can split PST files in multiple small sizes. It can support all versions of Windows OS and even it can support all versions of MS Outlook. It has a demo version that can help users to convert 25 items from each folder. It has technical support 24x7, users can get help by mail or live chat.