An old OST mailbox can be migrated to Office 365 if the original OST file is available and readable. The situation is different when the old Outlook profile or Exchange connection is no longer accessible, because normal Outlook export may not be practical. In that case, an OST to Office 365 migration tool can read the available OST and transfer its mailbox data to Microsoft 365. Softaken OST to Office 365 can scan the OST file, preview folders and email content, and export selected OST data to a chosen Office 365 account. It supports older Outlook-created OST files and large OST databases. Before starting a complete Office 365 migration, test one old OST file first and verify emails, folders, contacts, and other required mailbox data in the destination account.