To manually migrate OST to Office 365, you can follow these steps:
Export the OST file to PST format.
Import the PST file to Office 365.
To export the OST file to PST format:
Open Microsoft Outlook.
Go to File > Open & Export > Import/Export.
In the Import and Export Wizard, select Export to a file, and then click Next.
Select Outlook Data File (.pst), and then click Next.
Select the OST file that you want to export, and then click Next.
Select the Options that you want, and then click Finish.
Outlook will export the selected OST file to a PST file. You can then save the PST file to your desired location.
To import the PST file to Office 365:
Go to the Office 365 portal.
Click Mail.
Click the Settings gear icon in the top-right corner of the window.
Click View all Outlook settings.
Click Mail > Import.
Click Import from another email client.
Click Outlook Data File (.pst).
Click Browse to select the PST file that you want to import, and then click Next.
Select the folders that you want to import, and then click Next.
Click Finish to import the PST file.
Greetings,
Peter
forum.app.net
