Do you ever mail a letter and wonder what happens to it after you drop it in the box? Read all about the post office and learn how letters are weighed, sorted, transported, culled, canceled, coded, binned, boxed, and sorted once again. Find out how people and machines work together to deliver the letters you send. Children's Books of 1982 (Library of Congress)Do you ever mail a letter and wonder what happens to it after you drop it in the box? Read all about the post office and learn how letters are weighed, sorted, transported, culled, canceled, coded, binned, boxed, and sorted once again. Find out how people and machines work together to deliver the letters you send. Children's Books of 1982 (Library of Congress)