To import OST to Office 365 mailboxes, one can take a trial tour with the help of the trial version of Shoviv Outlook Suite tool. It is safe, fast, and easy to use. Using this tool, users can import accessible and inaccessible OST files into Office 365. This tool also provides easy options to import PST files, repair PST files, merge PST files, split PST file, and compress PST file size. I would also suggest you download a demo version to know its features and working process.
Read More: https://shovivtools.wordpress.com/ost-to-office-365-migration/