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.
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