It also made it a pain in the butt to use a socks proxy with it. Moreover it failed to un-base64 images in emails (failing to display them), when I tried to make it open an image it would just pass the base64 string to mpv instead of bothering to un-base64 it.
I moved to mutt since then but I do want to try some other emacs clients (mostly due to the emacs and org-mode integration).
But many users stick to it as its scoring system to prioritize emails is great at handling thousands of emails from mailing lists.
Mu4e and notmuch have excellent clients for Emacs. I slightly prefer notmuch as it has a simpler UI. Mu4e is a bit more polished, but I found its mail compose setup much less friendly than Gnus or notmuch.
One can set up notmuch as an excellent MUA centered around saved searches. I prefer such a workflow to tags or folders:
Have you ever tried mew? I heard a few good comments about it in the past but I have no idea how it compares to these clients.
Mu4e and notmuch are Gmail-like clients. Quite modern and well-maintained. Centered around searching and tagging.
One thing that I noticed with gnus was that it seemed to be very slow in threading messages (when dealing with more than 10000 headers). I'm not sure if it was a problem with my configuration though.