This letter gives a slap on the back to someone who's recently made it through a rough time.
1234, Main Street
Boston, MA 02123
07 April, 2005
<Recipient Address Goes Here>
Please allow me to congratulate you on the way you handled a very difficult time with <circumstances>. I know that the past <time> have not been easy for you, yet you persevered and came through the ordeal with flying colors. Your grace and strength in the face of adversity are so admirable and stand as an example to us all.
I just wanted you to know that I appreciate how far you have come. I hope you will treat yourself to something special to celebrate your making it through such a tough time.
encl: <List of enclosed items goes here>