There have been a few new options popping up for email clients on the Mac. I'm still sticking with [MailMate](https://freron.com/) (for very nerdy reasons), but [AirMail 3](https://www.macstories.net/reviews/airmail-3-review/) is looking great. This one is open source and easily extensible, so I'm pretty curious to dig in and see what it can do.