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).
Signatures if You're Emailing. If you are sending your cover letter or inquiry letter by email, end with a polite sign_off followed by your full name. You do not need to sign a cover letter that is being sent electronically. Write out your full name in the same font as the rest of the letter, and there's no need for italics or a handwriting font. The formatting here is very similar to an uploaded cover letter. However, emails do not contain a header with your phone number or other contact information. It's a good idea to include these details in your closing paragraph or after your typed signature. That makes it easy for the employer or networking contact to get in touch with you.