I also used Thunderbird exclusively for a long time, but recently switched, because the rewrite brought a lot of UI problems for me and even some vanishing data with the CardDav contacts. At the moment I use Evolution, the standard Groupware suite of Gnome/Cinnamon/... , which I avoided for a long time because Thunderbird was better at the time. I noticed that it is quite stable now and doing the basic jobs very well and has a good desktop integration (no struggles with thunderbird tray icon!). And Evolution also has Caldav Integration for Notes.