Allowing users to right-click on an email to begin the process of making a new email rule would be an increase in productivity. The right-click menu right now is small. This is okay, but there is room to add a few common setting options, this being one of them.

To clarify, it would be better if all the rule-making happened in a separate window, this way users do not need to click the "<-- Inbox" link just to go back to email inbox. Imagine setting several email rules this way, it provides friction that doesn't need to exist.