Here are 3 examples that you can use for resignation letter as Assistant Professor -. Resignation letters should use the formal greeting: "Dear".The first sentence in the letter should state that you are resigning and when. I am writing to formally tender my resignation from my position as an Assistant Professor at Crestwood High School, effective June 20, 2053. The letter should be signed and attached to a cover e-mail. The date of retirement would normally be the end of either the fall or spring semester. Complete a Withdrawal of Resignation Form; Photocopy the form for your records.