PAUL SMITH
2365 S Mayfield Ave
Chicago, IL 60652
Cell: (123)-555-1234
[Subject: Normally bold, summarizes the intention of the letter] -Optional-
Dear PAUL SMITH,
Thank you for your most thoughtful offer to look after my cat during the overseas trip I had planned. Due to unforeseen circumstances I have had to cancel my plans and will not be travelling away. Despite this, your offer and generosity will not be forgotten and hopefully I can be of assistance to you some day.
Sincerely,
Ross