An ideal time to let them know about your resignation is after you give your two weeks' notice and understand the details of the transition process. State the Position You're Resigning From With An Effective Date.Taylor discusses 6 key aspects of writing a resignation letter, including when to give notice, what to say, how to format it, and how to deliver it. Create a clear subject line. Many companies require a formal resignation letter to have on file. For those in more traditionally professional fields such as law, finance or politics a formal resignation letter may be more appropriate. I will be sure to complete any outstanding projects to ensure a smooth transition. If I can provide any further assistance, please let me know. Lastly, use a formal signoff. I hope this email finds you well.