"Why can't your email client remember that" - Gmail can figure this out, its a lab feature. Enable it. (See how I assumed you use gmail :), its probabilistic reasoning in action!)
What's the lab extension called? I can't find it. The closest I could find was "Got the wrong Bob?", but that only warns you after you pick an unusual Bob. Sounds like a dirty hack which wants to parade as a clever feature. They should instead just fix the ordering of the auto-suggest dropdown.