What is missing is leaving the experience alone, instead of trying to shove everything under the sun into it, including buggy AI and calendars, and making slow

What is missing is leaving the experience alone, instead of trying to shove everything under the sun into it, including buggy AI and calendars, and making slow Electron apps. Sparrow was a fantastic email client. Had it been left alone, apart from UI tweaks to match the OS and compatibility fixes, it would probably still be near perfect.