17 TN. "La structure restante de la lettre . . ." For Derrida, writing is always that which is an excess remainder, un reste . Further, in French, mail delivered to a post office box is called poste restante , making the dead letter office the ultimate poste restante , literally "remaining mail " Thus, Derrida is saying that Lacan's notion that the non-delivered letter, la lettre en souffrance always arrives at its destination overlooks the structural possibility that a letter can always remain in the dead letter office, and that without this possibility of deviation and remaining--the entire postal system-there would be no delivery of letters to any address at all.