If, for whatever reason, you’re looking to switch from Gmail, I think you’ll love FastMail.
Its workflow, interface, and features will be immediately recognizable to you: it has conversation view, archiving, spam detection, categorization, filtering, keyboard shortcuts, a modern and fast web UI (ditto for mobile), fast search, calendars, contacts, two-factor authentication, and the option to use your own domain name.
I’ve looked around and having even just that first one (a conversation view) is a shocking rarity in either webmail or mail apps. Let alone all those features.
Switching is easy too. You can import email directly from Gmail and can just export/import any calendars and contacts from Google. Plus, for any shared calendars that you still want to host at Google, you can have FastMail show them and sync any changes.
The big catch of course is that it isn’t free. But it’s not expensive either.
I know this post reads like an ad, but I’m just genuinely pleased so far (and I’m intentionally not using a referral code on the link above). Hopefully the next person doesn’t have to do as much comparison shopping as I did.