There are a number of things that mu4e does not do, by design:
emacs. In addition, mu4e piggybacks on Gnus’ message editor; See (message)Top.
Thus, many of the things an e-mail client traditionally needs to do, are delegated to other tools. This leaves mu4e to concentrate on what it does best: quickly finding the mails you are looking for, and handle them as efficiently as possible.