Dear Sir (name):

I appreciate the letter you sent regarding the end of your tenure. It has been a privilege working with you these past x amount of years. The benefits you’ve brought to this department through your efforts in the areas of…….. and …… will be felt for years to come. I, personally, have learned a great deal about …….. from working alongside you.

Your replacement will be welcomed with enthusiasm. I am sure you’ve done a lot to allow for their transition into this position with as much ease as possible and am looking forward to assisting them become familiar in this new role and supporting them as they grow in this field.

It has been an honor working with you and I look forward to your presence and valuable input on our various projects in the future. Please know you have my respect and heartfelt wishes for continued success in all your future endeavors.

Sincerely,

your name