How To Write A Letter Of Interests . A letter of interest is a formal document sent by a potential applicant to a company that has not advertised a job opportunity. The first and most important thing to remember about writing a letter of interest is. Application Letter Of Interest Sample / 7+ Free Promotion Application from sianlancaster.blogspot.com A letter of interest really isn’t so different from a cover letter, save for the fact that the job you’re interested in doesn’t exist yet. How to write a letter of interest 1 write it like a business letter. Encourage the reader to reach out to you.