This is a very useful addon ! A timesaver in mail follow-up.
Just a pity there is an icon problem : the icon which can be dragged to the mailheader toolbar, doesn't have a graphic, it's just a small empty button.
Actually I'm on TB 52.4.0 (32bit) and am sure the problem existed in TB 51.1.1 but don't know in what TB-version it started.
Is this recognizable ?
I contacted the author several times about this, without luck.
I remember, a while ago, the mailredirect addon had the same problem. Tha author reverted a Windows XP styling for the addon, and everything was ok.