From my inbox (with personal identifiers removed):
Dear Prof. Mankiw,
I am XXXXX, a PhD student majored in Economics at XXXXX University from this fall.
In fact, my son was born yesterday. I have been thinking of which name to give him for a long time, and decided to name him “Gregory” like your first name. The reason why is that I love your Macroeconomics textbook so much! Reading your book helped me see how interesting Economics is. And, you can see the consequence of your book by looking at my major at the moment. :D
I sincerely hope my son would become a great economist like you in the future.