Archive message is good, but 'Cancel' button is missing. So, the appearance is: only choice is click ok?
Also probably don't need archive at root (a curious person like me, might click it just to see what happens).
Idea!
I think that you could relocate the archive button to the "Selection" sub-menu (archive can be next to the move button); so, then we can archive only what is selected. That would be helpful.