Thunderbird v15 and later will prompt for authentication / biometrics before revealing account passwords. https://github.com/thunderbird/thunderbird-android/pull/10031 Thunderbird doesn't have any feature that prompts for biometrics or a password to launch the app. Several phone manufacturer's include such a feature packaged with their OS, allowing users to lock apps. Samsung secure folder and Oneplus app lock being two examples. Third party options are also available in app stores. If you have a specific idea in mind, feel free to make the suggestion on Mozilla connect linked below, there users can vote for it. https://connect.mozilla.org/t5/ideas/idb-p/ideas/label-name/thunderbird%20android