1) I am writing to extend/convey my heart-felt thanks/sincere appreciation/gratitude to you for…
2) I find an ordinary “thank you” entirely inadequate to tell you how much…
3) I must thank you again for…
4) If you need any help to …please let me know.
Dear Mr. and Mrs. Smith,
I am now back to China safe and sound. In this letter I would like to convey my heartfelt thanks to you and your lovely children for your kindness and hospitality to host me when I was in New York. Your generous help and tender care made me feel warly welcomed and transformed my first American trip into a beautiful memory.
I do hope that your whole family pay a visit to China in future, so that I could have the opportunity to repay your friendship. I assure you that you would enjoy visiting here as I did at your home.
I feel obliged to thank you once more.