A big +1 for fastmail, but their official ios app is 0/10 the last time I used it. Not a big problem if you use mail.app or their website on desktop.
Something I've done and which has been a big quality of life improvement is to set up a folder with 30 day retention, then an email rule to move any emails with `+` or apple relay there. Those are legitimate emails I want to read such as online order status, but I don't need them in my every day email.