You can try using WebbyAcad PST file exporter tool which can export PST file to Office 365 effortlessly. If you are using Outlook 2016, export your PST file from Outlook and add that in the tool. Preview your emails, choose those emails which you want to selectively export else whole inbox. Choose Office 365 from export options and enter your ID and password. As the software authenticates the information, it will automatically start the export process.