Dear Mr. & Mrs Smith,
How are you?
I am writing this mail to let you know that I have landed safely. Everything is going well now, please don't worry.
I am missing the days that I was living with you as an exchange student. You helped me a lot, it was an unforgettable experience for me and I really appreciate it, hoping to have the chance to treat you in China. You will be warmly welcomed by my family. We can take you to lots of fun place of China.
Looking forward to hearing from you soon!
Best regards
Yours sincerely
Liu Yang