A resignation letter is a formal document that an employee submits to their employer to announce their intention to leave their job. It serves as an official record of the resignation and typically includes essential details such as the date of submission, the intended last working day, and, if appropriate, a brief explanation for the departure. While it's not mandatory to provide a reason, expressing gratitude for the experiences and opportunities gained during employment can help maintain a positive relationship with the employer. The tone of the letter should be professional and respectful