Official email ending phrases

http://www.blairenglish.com/exercises/emails/exercises/formal-writing-vocabulary-list/words/starting-and-ending-phrases-formal-email.html

https://www.easypacelearning.com/all-lessons/english-level-2/1123-letters-and-emails-opening-and-closing-phrases

https://www.english-at-home.com/business/how-to-start-and-end-a-business-english-letter-or-email/

https://english.stackexchange.com/questions/332/which-expressions-can-be-used-to-close-an-email