No there's nothing mandatory and i said i have never seen anyone get scolded for not doing it. It's just common sense , it;'s being thought in communication courses etc just like when picking up phone you first say greetings, say company name, then your name. Because caller usually knows company and greetings but is having hard time catching your name if it;s first thing to they get "shot" at them upon you answering the phone call.
Last thing is typo from smartphone,, holding door and order of recipient in email doesn't belong to the same sentence. .
So you say we should order the list but only the wrong way to do it is to order it according to the achievements or importance of the recipient?