In case you are using Hosted Microsoft Exchange service and the server is hacked, you can't use your email, access old emails, or fix the problem. With an Offline Outlook data file (.ost), you can restore and move all mailbox data to Office 365/ Microsoft 365. Stellar Converter for OST Technician edition migrates OST files to M365 while retaining the original folder hierarchy. Thus ensuring quick migration without any data loss.