To convert OST to MBOX easily, you can use Advik OST to MBOX Converter. It works on all Windows versions and supports all Outlook OST files. The tool converts multiple OST emails to MBOX with attachments without losing any data. You don’t need any email client, and it keeps all emails, folders, and metadata safe. The converted MBOX files can be opened in Thunderbird, Apple Mail, Eudora, SeaMonkey, and more. A free demo is also available to test the software.