Want to know how to write a retirement letter of resignation? Get the insights you need and free retirement letter template to help guide the way.Use one of our resignation letter templates. Your retirement resignation letter should begin with a header that states the contact information of the sender and addressee as well as the date. This manual is designed to assist hiring managers with appropriate hiring processes and Human Resources practices. In the opening paragraph, make it clear that you are retiring. A retirement letter is a type of resignation letter, but the main difference is its purpose. The letter appears to be a formal resignation letter, which is typically a public document. Since, in the relieving letter, we mention a phrase, viz. TORONTO (AP) Canadian Prime Minister Justin Trudeau has announced his resignation after nearly a decade in power.