How to write a resignation letter that's effective immediately? Commence your letter with a formal salutation and a concise introductory paragraph.Learn how to write an immediate resignation letter with our comprehensive guide, including tips, examples, and a customizable template. A one (1) week notice letter is written notification provided to an employer that an employee will no longer be working with the company within seven (7) days. In this article, we cover everything you need to know about writing a resignation letter without notice and provide an example to get you started. Be Concise and Clear: While expressing gratitude is important, keep the letter concise and to the point.