Thank you so much! I'm quite sure this helps indeed the original author.I'm still curios about a keyboard action thought. But probably that is just not available.
By the way, as workaround, it seems that you can press the letter "m" to "Mark/Unmark the message as read".(Note that, if you are coming from GNOME Evolution, that is CTRL+K there, like "OK", quite mnemonic. If you want to change this shortcut in Thu...
