✔ 最佳答案
First of all, you should seek the consent of your employer the need of sending your personal note to the company's customers on your leaving from the employment of the company.
If OK, then you could simply write a note
“ I just write to you that I am going to leave the company with effect from 1.1.2009. I sincerely thank you for your kind support to my company and me. Thank you for your kind attention. “