Thunderbird is an email, news, and chat client created by the Mozilla Foundation. Thunderbird uses the MBOX file format. The most significant reason for this Thunderbird backup is to protect your essential data and provide a backup copy. If you can’t get your Thunderbird data for any reason, it’s getting frustrating for anyone. If you have a backup of your Thunderbird mails on an external drive, users can easily access the data from their computer.