Yes, you can migrate OST files to Office 365 without using Outlook by using a software Aryson OST to PST converter tool. Since Office 365 doesn't support direct OST file imports, these tools allow you to convert the OST file into a compatible PST format, which can then be uploaded to Office 365. These tools are designed to handle large data files and offer a quick, seamless migration process. They also support other email platforms like Gmail and Thunderbird, making them a versatile solution for managing OST files without requiring Outlook for conversion.