If you want to open an OST file in Outlook, you can first convert it into PST format using eSoftTools OST to PST Converter Software. This reliable tool helps users access OST mailbox data by converting it into a PST file that can be easily imported into Outlook. It supports the recovery of emails, contacts, calendars, notes, and attachments while maintaining the original folder hierarchy. The software provides a simple interface and preview option, making it easy to view and export OST data without any risk of data loss.