How do you know for sure whether or not to use a closing? One good test is to ask yourself whether this email is more akin to an instant message/text or a business letter. If you're giving your teammate a quick update on an ongoing project, a formal closing might not be necessary; if you're throwing your hat in the ring for a promotion, it definitely is required. When all else fails, and you're still not sure, err on the side of caution and include it. You'll never go wrong by being too polite and respectful.
Salutation: (Two lines below the recipient’s address, or about 1Ǚ down the page) The person the letter is intended for. Avoid “Dear Sir/Madam” and especially “To Whom it May Concern” unless absolutely necessary; not directing a letter to an exact recipient suggests that you don’t care who reads it (or you would have made a call or checked their website) _ and may prevent the letter from reaching someone who can act on your letter.