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Actually I haven't. I used to use it on an old macbook but it became buggy. I'd consider using it if you think it would be suitable

It's what I use and it meets all your requests except maybe the hotkeys.

Ok, I'll have a look. Mac OS lets you change the hotkeys in the menubar anyway, so not a back idea

I use default Apple Mail. It meets points 1, 2, 4. 3 can be somewhat configured like you said.

Thanks for the suggestion