Department will be utilizing a new template format. Instructions for the template are included as Enclosure 1.Enclosures. An enclosure can prevent a letter from becoming too detailed. In this article, we explain what an official letter is and how to write one, plus we provide a template and example of an official letter for you to reference. Add an enclosure notation after your signature at the end of the letter, and abbreviate it with "Enc." or "Encl. In the sample letter, fill in your personal information. Be sure to download and save the form to your computer before completing it. Permit Process Information. SUBJECT: Comprehensive Onboarding and Offboarding Program.