The android client does not have any filtering capability. The idea has been suggested by community members. You can show support by up-voting the idea linked below on Mozilla Connect. https://connect.mozilla.org/t5/ideas/filtering-with-android-thunderbird/idi-p/61144 An alternative is to apply your filtering rules at the server level where possible. Many email providers support this to varying levels. Server filtering has the advantage of being reflected on all clients, desktop & mobile.