A company can't force you to reveal why you are leaving, that would be illegal. To be professional and avoid burning any bridges, just keep the message short and direct.How to write a resignation letter that's effective immediately? Employ a traditional letter format. It's time to quit the job, and you're not giving two weeks' notice. Here's how to politely write a resignation letter, effective immediately. I'll give you my 6 best tips on how to write a formal resignation letter so you can professionally resign from your current job or post. Like my manager at my last firm was the reason I was leaving as she was lying and targeting me from the very beginning. What do you say in a letter of resignation? You don't want to blow this.