Yes, the UI is the mechanism that pops up the messaging, but the UX is the consideration of how the message will be used or misused by the user.

Ha, a terrible sentence. That's why I'm a back-end not a UX person :)

It's definitely a blurry line a lot of the time but having worked with a UX guy who was part of our design department, he definitely added a lot of value to the design process.