Comment by presto8

I have a very similar setup, but using gnus, mbsync, notmuch, and afew. All mail stays on the servers (including a self-hosted dovecot server on my home network). I manage about 10 email accounts with very little effort. It's easy to get extremely customized behavior by overriding defaults with elisp. Previously I was using Thunderbird, but I feel my emacs setup is much more productive.