I switched off of Gmail to Hey last year when the hype train was at full steam. Hey was... okay, but missing so many features that Gmail had. Most importantly to me was literally any calendar integration, and custom domain support.

Instead of going back to Gmail I found Fastmail after doing some research. It's just exactly what I want, a fast web based client that has the right features. And nothing else. Bravo to the company that makes it :)!