So much easier to use Neomutt with native IMAP support, without all the fuzz for local storage and I/O (mbsync and msmtp). Less than 300 Mo to cache all messages headers and thousand of message bodies since 2016.
~/.cache
» du -sh neomutt
267M neomutt
Lots of additional goodies compared to Apple Mail (diff highlight, better threading support and sorting options):
