For OST to Office 365 Migration, multiple manual and third-party solutions are available. If you have an OST (Offline Storage Table) file that you would like to import into Outlook Office 365, here are the steps you can follow:

1. First, make sure that you have the latest version of Outlook Office 365 installed on your computer.
2. Next, open Outlook and click on the "File" tab in the top left corner of the window.
3. In the "File" menu, click on "Open & Export" and then select "Import/Export" from the list of options.
4. On the Import and Export screen, pick "Import from another program/file" and hit "Next."
5. Select "Outlook Data File (.pst)" as the file type and click "Next."
6. Hit the "Browse" button and navigate to the location of your OST file on your computer. Select the file and click "Open."
7. Choose the folder you import the data into and click "Next."
8. Select the options you want to apply to the import process, such as if you wish to import subfolders or whether you want to import duplicate items. Click "Finish" to begin the import process.
9. Wait for the import process to complete. It may take a few whiles, according to the OST file size.

Once the import process is complete, you should see the imported data in the specified folder in Outlook.

Importing an OST file into Outlook Office 365 can be a helpful way to transfer data from one email account to another or to back up essential email data. Following these simple steps, you can easily import an OST file into Outlook Office 365 and access your email data whenever needed.

you can import the local Outlook OST file into Office 365 for mailbox migration. However, Office 365 does not support OST files. You need to extract the mail items from the local OST to PST format to import the mail items into Microsoft 365 mailboxes.

Regards,
Jimmy