Thoughts on Thunderbird? I'm not thrilled with it, but it has all the functionality I need/expect, it's reliable, doesn't require much config, but has plugin capabilities. I'm using it now because my school email requires me to do the whole Outlook 365 thing. Once I graduate, I'm planning to switch to Mutt or Neomutt. They can handle OAuth, but only if you can get certain API keys, which the institution is not going to let me have. With vim + mutt integration, and dendron + vim integration, I have reason to believe that I could get really good dendron + email integration this way