The simplest and the best method to convert OST file to Office 365 is a software. You can try MailsDaddy OST to Office 365 Migration Tool for fast and safe OST data conversion. The best part of using the tool is that it does not necessitate the use of Windows PowerShell for exporting OST data. It is a brilliant tool to export single or bulk OST files without any issue. You also do not need to worry if you have the corrupted OST file. You can easily repair the damaged OST file and move to o365. It can support the highly damaged OST file and migrate to Exchange Online. It even supports orphaned, Exchange Server, IMAP or Hotmail OST files. The software also has the feature to export OST data into PST. Suitable for all versions of Windows and Outlook.
If you are looking for some reliable software then I suggest you download and use its Demo version.