[Tim Wood]

Just as a note; there were some fixes to our Mail integration recently to avoid brokenness in Mail's AppleScript support. Make sure you are running the latest version (v45.x.y or higher should be fine) before testing this. Once updating, it would be safest to use our Mail preferences pane to disable the rule and then re-add it (so that the new badness-avoiding form of rule gets added in Mail).