To whom it may concern,
I received your very anonymous little letter in the mail the other day. It came on a day when I was certainly in need of cheering up. As you letter stated, it did in fact, brighten my day. I thank you for the $10 tucked away inside. I will use it to by myself a little Christmas treat. What a fun and mysterious way to send a smile to someone. I hope to do the same for someone else in return.
Thanks Again (Who ever you are!)