69 N. Grant Street, Mid Lake City,
[Subject: Normally bold, summarizes the intention of the letter] -Optional-
Dear Mather Smith,
We would like to sincerely express our gratitude for giving us the chance to be of service to your organization the past 3 years. Doing business with you has always been very pleasant and rewarding.
Once again, our biggest thanks, and we hope we could still serve your company for many more years to come.