Be direct and to the point and, in the first sentence, acknowledge the receipt of their letter of resignation and formally accept it. In the US I would say it's not safe, at least not entirely.That's communication with your prior employer usually from the email address they provided. A company says they will not accept your resignation even though you have already resigned verbally and submitted your letter of resignation previously. Resignation letter is a notice, not a request. It's not something they can reject. Omit from giving excessive personal details in your short notice resignation letter! If you want to leave, then email the resignation letter to her and HR, do the notice and leave. It's as simple as that. I appreciate the board coming in on short notice last week.