I agree. Geary looks great and mostly works fine—I don't need extensions or calendars.
I did have an issue in early 2019 where parsing of contact names somehow got messed up, causing outgoing messages to not get sent. After a few productive days of sending emails I found twelve in my outbox that hadn't actually sent! I got scared and went back to Thunderbird after that, but I keep Geary installed and launch it from time to time to sync my mail.
