You can bind keys to operations including more complex operations than 1key -> command in any window manager or de. If your environment of choice doesn't allow this you can use xbindkeys or sxhkd.

Wayland excluded because in wayland this feature is either provided/enabled by the environment or impossible to implement for securities sake.

If you haven't already got it may I suggest you implement some sort of raise or run functionality so that say F6 could open your email client or focus it if its already open.