Importing an Outlook OST into Office 365 is different from importing a PST file because OST files are primarily designed for offline synchronization. For a direct migration, I would recommend using an OST to Office 365 migration tool. MailsDaddy OST To Office 365 Migration Tool provides an option to scan and preview OST mailbox data and migrate emails, attachments, contacts, calendars, and tasks to a Microsoft 365 mailbox. It supports selective folder migration, multiple OST files, date filters, and maintains the original folder structure. The tool can also be useful for orphaned or inaccessible OST files where Outlook cannot open the original mailbox. This approach is much simpler than trying to manually extract and transfer the OST data.