Hi Grace,
Difficult to know what to say. It's amazing how a birthday wish to you (and not in your name) becomes all about his distress.
I think as people have said it is best to respond as the person you are, as Grace. I think it would be easy to let fly at him, and he would deserve it for that email alone. But on the whole I think it's best to be the better person in all of this. He appears to be unable to conduct himself in what most would feel was a reasonable manner, but you can control your response in a way that doesn't let him "get away" with it but also maintains a level of courtesy.
It's easy for me to say as my parents are no longer around. But he should be behaving more reasonably than this.
All the very best, and big hugs!!
Ros