You can also migrate the Outlook PST data to Office 365 Exchange Online Mailbox by the Network Upload or the third-party solution.
And if you looking for a tool then I recommend the “A2Z Migrations for PST to Office 365”. It is the best and very reliable software to import the complete Outlook PST data with all emails, contacts, calendars, tasks, appointments, and attachments, etc.
Using this PST to Office 365 Migration Tool you can also move the bulk PSTs to multiple Office 365 Primary or In-Place Archive Mailbox at once or Parallelly.
For getting more details to visit: [url="http://www.a2zmigrations.com/pst-to-office365/"]http://www.a2zmigrations.com/pst-to-office365/[/url]

Import PST to Office 365 Software allows to Export PST mailboxes in Office 365 and Live Exchange Server swiftly. PST to Office 365 tool helps to repair damaged and corrupted PST file items easily. Import PST to Office 365 tool helps the users to maintain a proper folder hierarchy as it is before the process of conversion. - See more at: https://www.mozesoft.com/blog/how-to-import-outlook-pst-to-exchange-online-office-365/
https://www.mozesoft.com/blog/import-psts-into-office-365-via-pst-capture/

Create a new user account in Microsoft 365 and assign it the required licenses for email migration.
Open Microsoft Outlook and click on the File tab. Select the Open & Export option and then click on Import/Export.
In the Import and Export Wizard, select the Export to a file option and click Next.
Select Outlook Data File (.pst) and click Next.
Select the folders that you want to export from the PST file and click Next.
Choose the location where you want to save the exported PST file and give it a name. Click Finish to start the export process.
Once the export is complete, login to the Office 365 account using a web browser.
Click on the app launcher icon and select Outlook from the list of apps.
In Outlook, click on the gear icon in the top right corner and select Mail from the dropdown menu.
In the Mail settings, click on the Mail tab and then select Accounts.
In the Accounts page, click on the Import email accounts link.
In the Import email accounts page, select the option to import from an Outlook Data File (.pst) and browse to the location where you saved the PST file.
Click on Upload to start the import process.
Once the import is complete, the imported emails will be available in the Office 365 account.

Greetings,
Peter