Half a century ago today the U.S. Post Office introduced the ZIP Code—the Zone Improvement Plan Code—a system to help the postal service keep up with the nation’s rapidly expanding mail system. From 1943 to 1963, the amount of mail flowing through the U.S. postal system doubled from 33 billion pieces of mail to 66.5 billion, says the Smithsonian Postal Museum. For the 188 years before that, the mail had been sorted by hand. With volumes growing the postal service couldn’t keep up, and the ZIP Code was introduced as a way to help automate the flow of mail.

The roll-out of ZIP Codes faced controversy at the time, says Time:

“People were concerned they were being turned into numbers,” says Jennifer Lynch, a U.S. Postal Service historian. “They thought it was depersonalizing them.”

And depending who you ask, ZIP codes face controversy to this day. ZIP Codes, says The New Republic, morphed over time. They shifted from being purely a numerical system that defines “where we are to defining who we are—far beyond our mailbox.”

“Organizations—business, government—can look at the mass of people we’ve become and break us down into usable points,” says Nancy Pope, curator at the Smithsonian’s National Postal Museum. “While it was designed to help our letters travel faster, it’s become like an ID system we all agree to and all use.” …“he number that began as a sorting utility has since expanded far beyond our addresses. Today, our ZIP code determines how we are read by policy-makers, politicians, statisticians, pollsters, insurers, businesses, organizers, and marketers. Governments use ZIP codes to determine who gets what—and this, in turn, stokes our political divisions. Private companies use ZIP code information to determine if they will, or will not, move into our communities. Retailers collect ZIP codes from customers, which can protect against fraud, but also helps a consumer database marketer collect personal information on us without our permission.”

These shifts in how the ZIP Codes are used, says a report from the Office of the Inspector General of the Postal Service, are actually worth a whole lot of money:

“IBM computed the additional revenues and reduced costs that result directly from the ZIP Code, in all of its uses, postal and non-postal. The estimate shows that the ZIP Code adds close to $10 billion annually in value across the economy.”

Fears of being tracked or of having your individualism quantified aside, the automation allowed by the ZIP Code lets the postal service do what would otherwise probably be impossible, carrying “40 percent of the world’s mail to 5 percent of the world’s population“—even if most of it, at this point, is spam.

More from Smithsonian.com:

Mr. Zip and the Brand-New ZIP Code