Any respectable mail client has an option to notify the user when new mail is received, but clearly for that to work the program needs to be running or it needs to have a service running in the background. Any good program that is potentially running 24/7 has an option for running in the system tray. Discord, qBitTorrent, Logitech Gaming Software all have system tray functionality. You can start those programs in the tray, you can minimize or even close them to the tray. Why doesn't Thunderbird, in 2019, have this feature? Relying on third-party programmers to create add-ons for this function is lazy, and every single update puts those add-ons at risk of becoming obsolete. It's awful design-choice to not have this implemented in the program already. No other perpetually-running program I can think of forces the user to have it cluttering up the taskbar when it's not in use. Why can't Thunderbird get on board with the rest of the world of program design? Why? If I sound frustrated, it's BECAUSE I AM. I can't understand how you've gone so long without doing something so simple and obvious. You must be doing it deliberately, and in my opinion, there is literally no excuse for that to be a decision. Add system tray functionality to Thunderbird.