A few years ago I received a letter from a law firm in Madrid informing me that their client Graham Gardner had died in the Air France Flight 447 crash, leaving behind $10 million that was now mine to claim. In the letter, printed on crisp white paper and peppered with seemingly official credentials, Graham Gardner’s supposed attorney recounted his fruitless search for the extended family since the crash, and suggested that he present me as the beneficiary, so together we could share the money.

These 419 scams, as they are known, take their name from the section of the Nigerian criminal code dealing with fraud, and date back as far as 1920. But the contact via mail piqued my interest: Despite how absurd and badly composed the letter was, the accompanying stamps and logos gave it an air of officialdom, of plausibility. It shows how the letter can be subverted, and how a universal tool of communication also opens the door to criminality.

Communication has always facilitated crime, and the letter can be traced back thousands of years, with the world’s oldest known correspondence consisting of clay tablets used to ferry messages between the pharaohs of Egypt and the kings of city-states. But to become a criminal tool, the letter needed a form of distribution that could provide the sender with anonymity. The creation and evolution of the modern postal service provided that infrastructure, which then underwrote centuries of increasingly creative criminal acts.

Like many things people consider indispensable now, from GPS to microwave ovens, the U.S. Postal Service was created out of military need. The flow of intelligence and orders between Congress and military forces was considered essential, leading to Benjamin Franklin’s appointment as the first postmaster general in 1775. In other parts of the world, the postal service dates back even further. The cursus publicus, the postal system of the Roman Empire, is one of the earliest known examples. Created under the reign of Emperor Augustus, it used horses and stations located at specific intervals to ensure the smooth passage of goods and directives.

It didn’t take long for criminals to realize that the rise of the postal service also created opportunity for exploitation. Crime could suddenly be carried out from afar, with relative anonymity. Acknowledging this, in 1683 the United Kingdom’s Royal Mail created the world’s oldest recognized criminal-investigations authority, to be followed some decades later by the U.S. Postal Inspection Service (USPIS). Both would initially occupy themselves with traditional criminality, such as highwaymen targeting postboys—a crime that would peak with the Great Train Robbery in 1963—but they also reflected in their outlook the mores of the day. In the United States, the Comstock Act of 1873 prohibited the mailing of items relating to contraception or abortion, while in the United Kingdom the Royal Mail intercepted a first edition of Ulysses by James Joyce, on the grounds of obscenity.

Soon enough, the service would be turned on its head and used for more nefarious means, including mail frauds. The most notorious of these was carried out by Charles Ponzi, the mastermind of an investment scam that eventually took his name and was replicated the world over. Ponzi tried to take advantage of wildly fluctuating exchange rates following World War I, buying and selling international postal reply coupons and promising investors a 50 percent return on their money within 45 days. Postal inspectors were initially hamstrung by the fact he was able to pay off the early investors in his pyramid. With no complaints, there was no fraud with which to charge him. It took a story in a newspaper to spook his investors, and Ponzi ended up in jail on charges of using the mail in a scheme to defraud.

As mail crimes became more sophisticated, so too did the inspectors investigating them. With its own laboratory and technical specialists, the USPIS was at the forefront of forensic science, examining documents for authenticity, fingerprints, chemicals, and fibers. In 1971 Clifford Irving fraudulently extracted $750,000 from a publishing company, on the pretense that he had made contact with the reclusive billionaire Howard Hughes and was writing his life story. Irving was eventually brought down by postal inspectors who used handwriting analysis on the letters supposedly from Hughes, determining they were in fact the work of Irving.

Such a breach of trust is often at the heart of mail crime, and perhaps no case amplified this more than that of Jim Bakker, the televangelist host of The PTL Club. Dangling the carrot of a lifetime of annual vacations at his resort, Bakker used the mail and his television show to amass millions of dollars that he used to fund a luxury lifestyle. “The message is that you can’t lie to people and you can’t use the telephone and the mail to lie to people to get them to send you money,” remarked Deborah Smith, who prosecuted at his trial in 1989. In the case of Allen Stanford 20 years later, Clayton Gerber, a postal inspector, would also emphasize the mail’s intrinsic honesty, saying that Stanford’s victims were inclined to believe him because “people trust what they get in the mail.” Stanford was accused by the U.S. Securities and Exchange Commission of running a “massive Ponzi scheme,” later receiving a 110-year sentence for defrauding his investors of $7 billion and embezzling at least $1.6 billion for himself.

Stanford’s victims came from across the globe, demonstrating how the international reach of mail delivered by ship and then air aided such crimes. Some uses of international post were dubious more than criminal, such as when the Australian athlete Reg Spiers mailed himself home in 1964 to avoid paying for a plane ticket. (When another man attempted to copy Spiers’s feat a year later, he almost died in the process.) One ingenious criminal known as the jack-in-the-box thief used a similar technique, hiding himself on commercial flights and emerging midair to steal the mail. William DeLucia was eventually found out in 1980 when a trunk he was hiding in opened as it was unloaded.

But the internationalization of mail would also be used for darker, more devious crimes. In 1972 the Palestinian terrorist group Black September killed the Israeli diplomat Ami Sachori with a letter bomb sent to Israel’s embassy in London. The group, notable for using this method to attack its enemies, was actually following a path that goes back almost as far as the postal service itself. While Emily Davison is known for throwing herself in front of the king’s horse at Epsom Derby in 1913, two years earlier she had been sent to prison for “unlawfully and maliciously placing in a Post Office letter box a dangerous substance likely to injure” bystanders. Suffragettes often used ink to damage mail in post boxes, but they also resorted to crude letter bombs, sometimes containing liquid phosphorus in fragile glass tubes.

In the following decades, the letter bomb would become a common tool of political agitation. One example comes from the Scottish National Liberation Army, a small organization modeled after militants in Northern Ireland. The so-called Tartan Terrorists often turned to the letter bomb in their campaign against the British state, which reached its peak in the 1980s and 1990s, sending devices to figures including Margaret Thatcher and the Princess of Wales. The letter bomb also attracted fringe groups such as the Japanese doomsday cult Aum Shinrikyo. After using sarin nerve agent to kill 13 people on a subway train in 1995, the group sent a parcel bomb to the office of Tokyo’s governor in an effort to disrupt the police investigation, instead blowing off the fingers of a secretary.

The weaponized letter went further than just enabling small disaffected groups, however. It also attracted lone wolves, allowing them to effect outsize destruction.

Theodore John Kaczynski, otherwise known as the Unabomber, was driven by a conviction that technology was a threat to humanity—as espoused in his manifesto, Industrial Society and Its Future. Operating from his remote cabin in the woods of Lincoln, Montana, Kaczynski killed three people and injured many more between 1978 and 1995, with a series of letter bombs sent predominantly to universities. There was some irony in Kaczynski’s choice of the mail as his messenger. The U.S. Postal Service had been at the forefront of technological innovation since its inception, implementing delivery via pneumatic tubes in cities across the United States in the late 19th century, and even considering mail by missile before abandoning the idea as unworkable.

Across the Atlantic, as Kaczynski’s campaign of terror was coming to an end, Britain’s Barclays Bank began receiving crude letter bombs as part of a one-man extortion crime wave. “Welcome to the Mardi Gra experience” warned the bomber’s blackmail letters, whose pop-art design pushed some to suspect Situationist revolutionaries, art saboteurs, or even ex-military anti-consumerists. The reality was rather less remarkable. In 1999, Edgar Pearce, a middle-aged man who had prepared the letters on the photocopier at his local library, was sentenced to 21 years in prison for a campaign that had perplexed anti-terrorist officers and cost millions of pounds. And in March of this year, another man with a grudge demonstrated once again the power of the lone wolf to spread terror via the mail. Carrying out a series of deadly bombings in and around Austin, Texas, Mark Anthony Conditt was eventually tracked down by the common household ingredients he used in the bombs, later blowing himself up as he was surrounded by a police SWAT team.

A week after 9/11, a number of U.S. lawmakers and journalists were sent anthrax spores via the mail. These events gave non-state threats a new focus within intelligence agencies. At the same time, the letter’s popularity as a tool of criminal enterprise was being challenged by the internet, turning it into a bridging point between the physical and the virtual. No case better demonstrates this kind of hybrid crime than that of the Silk Road drugs marketplace, where transactions were carried out on the dark web and goods sent by mail. It was notable not just for its inventiveness, but also in the way its promise of anonymity seduced people into crime. Using the Silk Road, one group of students at the University of Manchester—comparing themselves to characters from Breaking Bad—sold over $1 million of illegal drugs to customers around the world. Their ringleader, a petrochemical-engineering student with no previous convictions, received 15 years and three months in prison. The Silk Road mastermind Dread Pirate Roberts was eventually brought down by the FBI, but only after he had effectively opened Pandora's box. Similar operations are now fueling America’s opioid addiction, and as authorities crack down on legally prescribed drugs, they're increasingly finding that even more dangerous opioids such as fentanyl are being sent anonymously through the mail from China.

This anonymity is the beating heart of mail crime, opening the door for anyone with enough motive to commit criminal acts at arm’s length from the law. In the same way that the internet allows lone hackers to become bank robbers, the letter serves as a gateway for unconnected people to reach out to the world, whatever their intentions. It remains both a symbol of trust and a tool of terror, even as its power has seemingly diminished in the face of the greater anonymity offered by the internet, and the rapid changes in security apparatuses as the world has converged on the singular threat of terrorism in the 21st century.

As the explosion of crime on the dark web demonstrates, however, these changes have also seen the postal system, private or public, assume an ever-expanding role in our lives. As other means of local distribution contract in a globalized world, this technological marvel, born from military need hundreds of years ago, remains an increasingly vital connection between people and physical goods and materials—a powerful nexus that can be used to facilitate both the virtues and vices of humanity.