If you are looking for a tool to import OST files into Office 365, take the help of MailsDady OST to Office 365 Migration Tool.
Using this software users can import single or multiple OST files into Office 365 single or multiple accounts at a time.
It is helpful to display the preview of the overall OST file database before migration into Exchange online account.
To know more, visit here: Migrate OST to Office 365
Do you want to know how to import OST to Office 365? If yes, I would like to mention here the CubexSoft OST to PST Converter tool that easily exports OST to Office 365 cloud platform without Outlook. This software supports all versions, and it efficiently holds data of MS Outlook in an offline folder to access the data without connecting to the internet. The file size is not an issue to get satisfactory conversion results. you can download the free trial version which converts a few items from OST to Office 365 free of cost.