Close the letter affirmatively. Reiterate your recommendation of the candidate and, if appropriate, invite the recipient to contact you. For example, say, "For all of these reasons, I think Michael will make a fine addition to your team. Should you have any questions, I invite you to contact me at the number or address, above
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.