A Professional Greeting. Your letter should be addressed to your boss. There's a good chance that this letter will merely end up in a file in HR, but it starts with your boss. Assuming this is someone with whom you work reasonably close with on a daily basis, it doesn't have to be super stiff and formal. Specific and professional is the right tone here.
Do You Really Need to Write a Resignation Letter? Why Write a Resignation Letter? Do you really need to write a formal resignation letter? The short answer is that most of the time, no letter of resignation is necessary. Many people do believe that as an employee you need to formally resign from a job by writing a formal resignation letter to your current employer.