In this article, we explain what an enclosure is and how to cite one, and we provide an example of an enclosure in a business letter. The enclosure letter should be designed to serve those persons as well.How to correctly format a business letter. Includes detailed instructions and example on how to write a business letter for any situation. Learn the art of formal letter writing. Discover how to write and propperly format your formal letters. In Chicago style, headings are used to organize your writing and give it a hierarchical organization. Chicago style has specific rules for formatting headings. This resource covers the parts of the basic business letter and provides three sample business letters. Add an enclosure notation after your signature at the end of the letter, and abbreviate it with "Enc." or "Encl.