Wie richtet man eine weitere Email-Adresse ein?

' click the 'hamburger' menu in upper right (three horizontal stacked lines) - click new account>email

OR, since you may be new to Thunderbird, you may enjoy the menu bar, which is hidden by default. To activate it, - press alt key - when menu bar appears, click view>toolbars and tick 'menu bar' Now, you can create another account by clicking File>New>Email account