Dear First Name
I am writing this email to notify you that I am resigning from my current position at ABC. I will be serving my notice period of a month and my last day of working will be 15th June 20XX.
ABC has given me the best of opportunities and helped to learn and grow as a person. But one has to take a decision to grow further in career and take on new challenges.
I will always be grateful to you for being my manager and mentor and guiding me throughout for last five years. I am also very thankful to all my fellow colleagues for supporting me making my stay here as a memorable one.
I would be very happy to provide my complete cooperation and time to help you with a smooth transition. If there is anything else that I can do, please do let me know.
Please consider this email as my formal resignation letter and confirm on my last working day so that I can process the exit formalities accordingly.