It is established etiquette by the Joint Chiefs of Staff, United States Department of Defense, the U.S. Army, the U.S. Navy, and the U.S. Air Force that the closing “Respectfully yours” be reserved for the President of the United States (according to U.S. Army standards, this also extends to the first lady and the President_elect).
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.