This is just a good sample farewell letter to clients.
Re: Change of Service
I am writing to inform you that I shall be leaving Eternal Productions Enterprise at the end of this month. The time has come for me to bid you farewell as I move on in my career. Hence, I shall not be able to serve you and your esteemed company after this month.
Please allow me to thank you for a great business relationship during my tenure at Eternal Productions. It has been my honor and delight to have serviced you at Southern Precision Industry.
I hope to service you again in the future. I do hope that our paths may cross again. I wish you well and all the success in your future endeavors.