I had recently switched to KDE from Gnome and was looking for an Alternative for Geary. I really liked how fast Geary was and neither Thunderbird nor KMail could act as a replacement for my need(Simple and fast). Before giving up for another Electron app, I gave a try to Trojita and immediately fell in love with its speed. It was blazingly fast to the extent even Geary could never match! This is a simple guide to setup Trojita for Gmail.
You need to make use of App Passwords in Google Account in order to access Trojita through Gmail (The other way is to enable Less Secure App Access which doesn’t sound inviting!). App Passwords, in turn, need 2-Factor Authentication turned on.
After installing Trojita, you need to setup IMAP servers for Gmail.
Turn on 2- Step Verification
Set up App Passwords
Logging in with Gmail