December 1966 in Chicago's main post office. Ten million pieces of mail sit backlogged, and officials are reportedly discussing whether to just burn it all. The problem? The postal system that worked for a century was collapsing under its own success. Railway Mail Service clerks had to memorize up to 30,000 addresses, knowledge that took years to build and lived entirely in workers' heads. When someone retired from the Post Office, that expertise walked out the door. Three years earlier, the Post Office had rolled out a solution: ZIP codes. Five digits that promised to make everything faster and more efficient. But it wasn't really about speed, it was about making workers replaceable. In Episode 9 of our postal history story, Aileen and Maia trace how a Philadelphia postal inspector named Robert Moon spent 19 years getting rejected before his t ...