I use Mailspring on my desktop and an ever-rotating cast of not-that-great-but-fine options on phones.
I do recommend Mailspring if you’re one of those freaks that doesn’t solely use webmail on a not-phone computer.
Edit: Mailspring manages multiple accounts really well - you can easily switch between a unified or split out view of inbox, drafts, sent - and it’s got a strangely satisfying data-driven signature tool (you fill in the details you want to see in your signature and can then browse and edit layouts for those details).
I said up-topic I’m using Fastmail as my mail account provider, but I still have two Google accounts I look at and one Yahoo one.