How do I open an MBOX file in Gmail? Use the most promising MBOX to Gmail converter program, it will help you to about how do I open an MBOX file in Gmail including complete data intact such as; header items, attachments, images, etc. By using MBOX to Gmail converter you can open multiple MBOX files / folders data on any Windows OS without tempering any existing data. Download the edition of this tool to test its working ability.