Another reason to have it, is that a single click of the systray icon should open the window and bring it to the foreground. Clicking it again in the systray, without having to move my mouse, should hide the window again.
I will echo the opinion that others have written here: This is how many other apps behave in the systray and eM client should mirror that behaviour for a consistent user experience.
One of the recent updates makes it so that eM Client will no longer open when clicking it from the taskbar if it is already running. I’m not sure if this is related, but it’s annoying.
Hopefully this’ll be helpful to all those who are annoyed that this hasn’t been fixed in Em Client yet.
I’ve found a workaround by installing ‘4t Tray Minimiser’. This small app is free (though there is a paid version), and it adds a window button to all apps for minimizing to the notification tray. Once minimized, the app can be brought back up again by a single click on the tray app icon, which is always displayed. It seems to work perfectly for everything, not just Em Client.
Hopefully this will help all those that miss this basic functionality in Em Client.