I use Fastmail on the web, and Aqua Mail as my Android client.
The joy of using almost any enail servie other than Gmail or Outlook is that you can use basically any IMAP client you want :). Yes, I know that they both also support IMAP, but it never seems to work quite as well as one might hope.
Depending on the complexity, there’s also
abbrev-mode
: https://www.gnu.org/software/emacs/manual/html_node/emacs/Abbrevs.html