[Evolution] Toggle read/unread key bind?

[Matt Connell <matt connell tech>]

I found how to enable/set my own keybinds (in .config/evolution/accels)
but I was interested in defining a new accel that doesn't seem to
already be defined.

I'd like to have a key binding to toggle read/unread status on a given
message.  This is an operation I do a lot and would save me some time.

Is this possible?