Rated 4 out of 5 stars

Does what it says, just add the button to the message editor and hit it. Sender and receiver are filled in automatically, if needed.

4/5 Stars, because it's missing a filter-action. This way you could autorespond to spams, your stalking ex-friend, or your business contacts.

This review is for a previous version of the add-on (0.18.0). 

Thank you for the idea. I'll see if a filter action makes sense.