I'd mostly used Macs for like a decade before I gave Mail a try. Just didn't occur to me. Takes a while to break the "first party and/or default is probably not acceptably-decent" mindset. I've found it entirely OK. Good enough it's not at all worth searching for something better (for me—email needs vary greatly, I'm sure)

Kinda like getting used to drag-n-drop usually doing something sensible, rather than its fucking everything up, doing nothing, or causing a crash/state-corruption in the target program. I'd been trained by other platforms to just about never try to use it for anything except dragging files from directory to directory, and had to un-learn that.