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.
Opening Part: The first paragraph of the mail writing must state the introduction of the writer. It also contains the previous correspondence if any. Main Part: This paragraph states the main idea or the reason for writing. It must be clear, concise, complete, and to the point. Concluding Part: It is the conclusion of the business letter. It shows the suggestions or the need of the action. The closing of the letter shows the expectation of the sender from the recipient. Always end your mail by courteous words like thanking you, warm regards, look forward to hearing from your side etc.