Dear Mr. Smith
I am writing to you this letter because I wanted to thank you personally for your valuable contributions to our department.
Ever since you worked at our office, the company has grown so much in terms of size and profitability. You have brought fame and honor in this company. Because of you, the company has become one of the best in the business.
It is hard for us to let go of an employee like you. You are one in a million. However, I know that you have your own reasons for leaving the company.
Again, I wanted to say thank you for your great efforts for making the company on top. I wish you all the best life for your retirement.
If I can be of assistance, just give me a call or simply drop by at my office.