Another thought: when people complain about the state of Linux email clients, what is so good about the Windows alternatives? Office productivity suites, I get it. But email clients all suck. Mutt's mantra is so true, at least they're honest about sucking less. I believe Linux is a 100% of the time platform because the choice (again, user choice) to run minimal terminal apps means like less than average 50% memory ut…
Don't write off Outlook without a second thought. It's big with loads of features, yes - but that's what's good about it. If all you need to do is plain text email, sure, Mutt is fine. If you deal with a large amount of email, calendar appointments, tasks, contacts, etc, in a professional role, nothing beats Outlook. There's a reason it's so popular.
Searching with notmuch is blazing fast and works better than gmail search.
HTML email is handled by w3m. The new "eww" would probably work also but I haven't tried that yet.
It's possible to send HTML email by writing in org-mode markup, but I haven't done that either. If people can inflict their HTML email on me, they can deal with my plain-text replies.