Use a business closing and sign your name. Above all, be professional. If the you’re sending a physical letter, print it out and sign it by hand. Otherwise, just typing your name will do.
You are required to have three letters of recommendation submitted on your behalf. The letters should be submitted by instructors in a discipline related to your proposed field of study who are in a position to analyze your abilities and academic promise. Letters may be submitted online or on paper via regular mail; online submissions are strongly preferred.