Closing the Letter. Choose a Closing: One must use a proper closing in a business letter. Use a comma (,) after it. Sign the Letter: Always sign the letter in ink. If sending a printed copy, always affix the scanned signature. Make Note of Enclosure: One must properly enclose a list of attached documents with the letter. One can use the abbreviation of the enclosure, i.e., Encl. or Enc.
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).