Since the developer of my previously favourite macOS mail client now thinks it's kind of stupid that he decided against a subscription model back then, I used the past weekend to familiarise myself with mu4e. Turns out: I don't miss anything. And I can - finally - use my mail configuration everywhere where GNU Emacs exists. :-)

Admittedly: The fact that you first have to set up mbsync and msmtp on each computer is a nuisance. But I have stored all the necessary configuration files centrally, so that it is essentially done with installing applications and copying files.

Impressions so far: mu4e seems to be a much more powerful and user-friendly mail client than mutt (which I somehow seem to be too stupid for), especially if you (like me) have a handful of mail addresses and actively use them.