If you have lost your OST database then one thing you can do with it is that first, you will have to convert that database into PST formats, vMail OST to PST Converter will also help to migrate your data into Office 365 so you can improve that cloud-based application. Apart from this, the user will be able to convert OST files into EML, vCard, MSG, and MHTML. It also supports Live Exchange Server.

Know more info- https://www.vsoftware.org/ost-to-pst-converter.html