I haven’t tried it yet, but Notion Mail is officially out for the Mac, with iOS “coming soon”.
I’ve been intrigued by it ever since Matt Birchler covered some of the unique features like command palettes, special layouts based on user defined email fields, and natural language example-based filtering:
Note that it only connects to Gmail accounts, and if you want to connect to multiple Gmails, it requires multiple Notion accounts, as far as I can tell.
It seems like everything is free base-functionality-wise except AI features, requiring the AI plan.