I miss using a TUI for mail but it looks like they haven’t really solved the most important reason I don’t, which is rendering HTML emails.
You can configure aerc to pass the email contents through an intermediate program depending on the MIME type. I believe it renders HTML through w3m by default or something like that. Of course it isn't full rendering with CSS and whatnot, but it is pretty good for most mails.
Not sure how practical that actually would be, but I can dream.