Although there weren't always Post Offices like we know them there's been some system for centuries. In days gone by any non-serf who happened to find himself in England or France or an equivalent kingdom such as Spain and had something to send could write out a note, fold it over, address the outside, and hand it to any royal official, who would arrest the letter-writer for high treason. The writer was tortured until he confessed to subversion, and was executed. The mortality rate was particularly high for magazine writers; some advice columnists were killed more than six times.
This process weakened over time, and by the 17th century was simply that letter-writers assembled their missives into mail sacks to be kicked into shreds by official Post Horses. Yet it would not be until 1932 that intense lobbying by the Hallmark Corporation earned the formal repeal of summary executions for birthday cards in England, and it would take until 1934 for Scotland, although they backdated it to 1933 to look less thoughtful.
This is about the time when you expect Benjamin Franklin to step into things, so let's see where that gets us. Franklin was inspired by a severe storm and next rainstorm tried to fly a stove on the end of a long string into Parliament. This failed completely, and his friends worried when he fashioned the result into a kind of humorous anecdote, they guessed, about two carpenters who were trying to fashion a sun they didn't know whether it was rising or setting into a spunky old woman. He insisted was just the first part of a plan wherein he would appear in a trans-temporal hallucination to the renowned science fiction author Isaac Asimov, whom he would order to build internationally-funded space stations. With Asimov given that task, Franklin tried to write everybody in North America about this, and finding no post office, realized this would take a while.
Well, that didn't get us much of anywhere. I'm sorry for that. Maybe we should have tried following the invention of stamps instead, and we'll see how that works next time.
Zip codes figured into things when people noticed it sounded funny addressing letters to ``Minneapolis, Minnesota''. All those `mini' sounds frontloaded like that made it sound like the city was nearly twenty percent smaller than it actually was. This was solved by adding a city code, so people would address ``Minneapolis 14, Minnesota'', which was such a huge terminology improvement people around the world started to write Minneapolis just so they could put the 14 there. Minneapolis today is ten feet higher up than it was during the Second World War, just because of the bulk of incoming mail that wanted that cool city code. And when you consider how all that bulk presses down the Earth's surface you realize that's a lot of mail, and the city's probably going to slip off the pile at some point, which could inconvenience Saint Paul.
But natural jealousy of Minneapolis meant code numbers expanded to places like Bloomington, Minnesota, for example Duluth or Rochester. From there it was bound to go nationwide since the United States of the late 50s simply could not ignore the fads sweeping Saint Cloud. The codes were to be applied nationwide, then, and the coding was done in Cobol, in order that Cobol programmers could be sure of long-term employment. It's come back to bite them, of course, because now they dread how anyone in the world is allowed to phone any Cobol programmer and demand the Zip code for any municipality. You're not supposed to know this, but ``44999'' is a ``cheat'' code which will get your letter to wherever it's supposed to go. Use it only for the most important stuff or they'll catch on and change that. Also try sending something to ``32787'' for an amusing easter egg.
The collapse of post office revenues recently and the troubles this implies for maintaining service can't be traced to any one person, of course. It is the fault of five people, and that's why we're waiting for them to --- THERE THEY ARE! GET THEM!
Trivia: When Cyrus H K Curtis and George Horace Lorimer took over The Saturday Evening Post in 1899 it had a circulation of about 2,000 and advertising revenue about $300 per issue. Source: Decline And Fall, Otto Friedrich.
Currently Reading: The Ultimate History Of Video Games, Steven L Kent. As it's a decade old I would hope not.