The direct method which involves exporting the OST files directly to Office 365 accounts and then ultimately creating the ost file in office 365 is the SysInspire ost to office 365 tool.
This method helps you to export your ost file to Office 365.
The following steps help in effective migration and thus leading to the creation of the ost file in Office 365:
Launch and open the SysInspire software.
From the main interface of the software, click the Browse button to select the OST file.
You can also click the Find button if you do not know the location of OST-file.
Click Convert to commence the conversion process
The software will display a preview.
From the main menu, click the Save Converted File option to office 365
This way you can directly import an OST file to your Office 365 account.
More info:- Convert OST to PST
Install the effective MailsDaddy OST to Office 365 Migration Tool to upload OST file to Office 365 without Outlook. An independent solution that works without the help of any other utility. It is a complete solution to convert the OST file to Office 365 without disturbing the internal properties of the OST. The tool is capable of importing even the highly damaged OST to Exchange Online mailbox. It also previews the complete details of the PST file before migrating to Office 365 account.