Dear Ms. Emily Clarke,. How to write a resignation letter that's effective immediately?Dear (HR Manager's Name),. (For example, "I regret to inform you that I will be resigning from my position, effective immediately. It is with regret that I have to resign my position as a nurse practitioner in the cardiac unit at UPMC East immediately. "I received your request that I submit my resignation in writing. Please accept this letter as my formal resignation. Today will be my last day of work. You should never sign a resignation letter under duress.