+1 for Spark. I know there are other clients that have snooze and ‘send later’ functions, but I’ve been using Spark for a couple of years and haven’t really had any complaints.
I use spark and mostly happy, but the fact that I cannot setup inbox rules (if subject equals then trash) is a bit frustrating.
This is the main thing that keeps me on Apple Mail. In any kind of work context it's absolutely required for me, and the other alternative mail clients mostly concentrate on being pretty, unfortunately.
You can set up those in Gmail directly.
Don't use Gmail for personal.
Another Spark user here. Works great. I'm also using the iOS version.