Me: Hi Ms. Richard, I noticed you emailed me about 50 minutes ago, how can I help you?
Her: Oh, hello, thank for getting back to me so quickly. I'd just like to inform you that, on behalf of George Mason University law school, you have been accepted and we would love if you would join us in our fall 2005 entering class
Me: Wow, that's really exciting to hear, I'm very enthused. I'm really interested in international law and I noticed that George Mason's law school was originally the (something) School of International Law." It seems like it'd be a great school for my interests.
Just say something normal.