A short resignation letter is the way to go. Include your name, position, the date of resignation and the intended last day of work in the first paragraph.State that you wish to quit and include your final day of work. It is my regret to inform you that I must hand in my resignation as head of security at Cornado Center. Then, state your intent to resign and exact date of departure. Provide a reason (optional) and then show gratitude. I'm emailing you to formally resign as (job title) at (company name). Add contact details, company name, and date.