Mail.app is fine for me... What am I missing in an email client that Mail.app doesn't provide?
"[...] it’s buggy and crashy, it needs to update my email library every few months when I open it (why does my email need a library?), and it lacks any sort of innovative feature set (or even support for things like snoozing)."
I can remember mail.app needing to rebuild a mailbox to a new format maybe twice or three times, since probably 2008.
1 person saying "x is buggy and crashes" doesn't mean much without actual descriptions of the problem.
I've used mail.app since I've used OS X, and I wouldn't describe any version I've used as particularly "buggy" or "crashy"
I realize this is just one data point, but as unpopular as your perspective is, stephenr, I share it.