Great for the end of projects and events, this goodbye letter is aimed at volunteers.
Dear {Recipient},
Now that your time with us is coming to an end, I wanted to personally extend my warmest thanks for all of your efforts in volunteering at our organization. You have put in the kind of dedication, efficiency and vigor to this project that I would expect from a tenured employee.
I wish you the best of luck with {school, traveling, etc.} and hope that you have the time to visit us again soon. Thank you again for all of your time and hard work. It was greatly appreciated.
Sincerely,
{Sender}