Work with panels in Email
Email has three panels: accounts, messages, and the open message. Your phone shows one panel at a time. To go back a panel, make the back gesture (learn how).
Email has three panels: accounts, messages, and the open message. In landscape, you see several panels at once. You can resize or hide these panels (learn how).
Checked against the LuneOS code and installed apps. Nobody has tried these steps by hand yet, so tell us if something differs.