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.
Tips and Tricks for Better Letters: Following the proper formatting is only the first part of writing a letter that gets action. The content of a poorly formatted letter is unlikely to be read _ in one study of HR personnel, more than 80% said they’d throw out a resume if there were only one or two errors in the cover letter _ but even a well_formed letter is unlikely to be acted on unless the content is powerful and engaging. Once you have their attention, you need to create interest in whatever you’re offering. Promise to solve their problems _ with a great product, with your services, with a partnership, with whatever it is you’re writing about.