You can convert OST files to MBOX files without having to install Outlook on your computer. Just use a dependable third-party tool like the GainTool OST to MBOX Converter. This expert solution can convert OST mailbox data into MBOX format without having to set up or install Microsoft Outlook. It safely changes everything in your mailbox, like emails, attachments, folders, and metadata, into MBOX format, which Apple Mail works well with. The software can be used on all versions of Windows and is compatible with all versions of Outlook.