If you want to open OST to Outlook, I would recommend the CloudXena OST to PST Converter for Mac. This utility can convert OST to PST and many different formats, such as MBOX, EML, ICS, etc. Also, this tool is designed to migrate OST to Gmail, Office 365, IMAP, iCloud, Thunderbird, and other email clients. It ensures fast, accurate, and seamless migration with advanced features like selective migration, maintaining folder hierarchy, and data integrity.