In the USA, it is customary to begin a letter with "Dear" and the name of the recipient. E.g., "Dear Dr. Smith" or "Dear Alex".
Was there a similar convention for the opening of a letter written in Latin in various eras? E.g., Classical Latin, Medieval Latin, Contemporary Latin, etc. What were those conventions, and which era(s) did those conventions belong to? I am guessing it changed over time.