Letter Text: Business letter text should be clean and readable. Avoid writing your letter in one large block of text. Break your text into several concise paragraphs. These paragraphs should be aligned to the left; this allows for easier reading. When you have completed your letter, ask someone else to read it for you. Have them glance briefly at the letter. Is there too much text on the page? Is it easy to see the distinct paragraphs?
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.