Definition

§ 4251. Definition (a) First class mail consists of mailable (1) postal cards, (2) post cards, (3) matter wholly or partially in writing or typewriting, except as provided in sections 4365, 4453, and 4555 of this title, and (4) matter closed against postal inspection. (b) A postal card is a card supplied by the Department with a postage stamp printed or impressed on it for the transmission of mes- 74 Stat. 664 sages, orders, notices and other communications, either printed or written in pencil or ink. (c) Post cards are privately printed mailing cards for the transmission of messages. They may not be larger than the size fixed by the Convention of the Universal Postal Union in effect and of approximately the same form, quality and weight as postal cards. (d) Drop letters are letters— (1) mailed for local delivery at post offices where letter carrier service is not established; and (2) neither collected nor delivered by rural or star route carriers.