If you can stick a stamp on it, chances are someone has tried to mail it. 

“Pretty much anything you could imagine has come through the mail at some point,” says Sue Brennan, a spokesperson for the U.S. Postal Service (USPS). In fact, Ripley's Believe It or Not! holds an annual contest for the strangest items mailed without being boxed up. In 2014, first place went to a tree stump embedded with a horseshoe.

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Stranger than fiction

If you were a fan of Jeff Brown's 1964 children's book "Flat Stanley," you may remember that after Stanley was pancaked by a bulletin board, his parents mailed him to visit friends rather than spring for airfare. A little boy in a storybook is one thing — the odd items people have really managed to mail are another.

A child. In the real world, soon after the U.S. Parcel Post Service began on January 1, 1913, some families began “mailing” their children. According to the Smithsonian National Postal Museum, the first child mailed was a little boy in Ohio who was escorted by a Rural Free Delivery carrier to visit his grandmother a mile away. The child's parents paid 15 cents for stamps and insured him for $50. Posting kids was banned in 1915.

Bricks. Once upon a time, recipients of unwanted junk mail may have been inspired by prankster Abbie Hoffman's 1971 book, "Steal This Book." to start a new fad: “The next one you get, paste it on a brick and drop it in the mailbox,” he wrote. “The company is required by law to pay the postage.” Regardless of how the practice started, USPS eventually caught on and in 1996 ruled any heavy items mailed with a business return label would not be delivered.

Glitter. Pranksters have been known to send letters filled with the shiny stuff as publicity stunts. Staffers for U.S. Congressman Jeff Fortenberry learned this lesson when a suspicious envelope was mailed to his Nebraska office. Law enforcement agents, called to the scene, discovered that it contained a bag of glitter and a protest letter.

A glitter-filled envelope that includes a spring-loaded device usually is referred to as a glitter bomb. Attention-getting yes, harmful, no. "Glitter in and of itself is not hazardous and can certainly be mailed,” says postal inspector Jeff Long. Long adds that USPS doesn't like to refer to them as bombs because they're not dangerous.

A cat. In 1897, postal officials in New York City propelled a live cat through an 8-inch diameter pneumatic tube for nearly three-quarters of a mile while testing a new system for moving mail between stations. According to the news report at the time, the kitty survived the trip.

Today, you can't post most types of pets. For instance, USPS is concerned that animals like dogs and cats won't arrive alive. They'll likely starve or become dehydrated because the agency doesn't allow them to be mailed with food or water; loose substances might damage the shipping container or nearby packages.

Suffocation is also a problem. In 2011, authorities charged a Minneapolis woman with animal cruelty after she tried to mail a 4-month-old puppy in a box without air holes. Fortunately, the puppy survived.

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A boyfriend. There are a number of documented incidences of people mailing themselves, including a slave in Virginia who escaped to Pennsylvania in a shipping box and an inmate in Germany who climbed into a box in the prison mailroom.

In 2012, a romantically inclined man in China decided to mail himself to his girlfriend's office in a shipping box. Unfortunately, the couriers couldn't find her address and her beloved passed out after being stuck in the box for nearly three hours. (He didn't make air holes in it.) 

Not-so-funny business

Peculiar parcels aside, weird mail potentially is hazardous mail. In 2014, postal inspectors investigated 2,546 cases of suspicious items, from mysterious liquids to possible bombs. Fortunately, there were no reported injuries or fatalities.

Recently in South Dakota, an air cargo facility under contract with USPS was evacuated for almost a week after workers discovered mercury leaking from a package. According to the Environmental Protection Agency, breathing in vapors from mercury can cause neurological symptoms such as hand tremors and memory problems — or worse.

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“Many common things in U.S. households are dangerous to mail,” says Brennan. The nine classes of USPS mail hazards include the following items that either can't be mailed or can be mailed only under strict conditions.

  • Explosives, such as fireworks and small arms ammunition
  • Explosive or toxic gasses, such as those found in cigarette lighters and some fire extinguishers
  • Flammable or combustible liquids, especially those with a low flashpoint, such as gasoline
  • Flammable solids, including oily fabrics and matches that can spontaneously combust (which means you can safely mail matches via surface mail but not air mail)
  • Oxidizing substances and organic peroxides, such as swimming-pool chemicals, which can easily combust.
  • Toxic or infectious substances, such as used health-care products, especially if they contain infectious substances.
  • Radioactive materials. (And if you have any lying around the house, postal regulations are the least of your worries.)
  • Corrosives. It's OK to mail common dry-cell batteries, but not the lead-cell type found in automobiles.
  • Miscellaneous hazardous materials. You can't ship any of the following via air mail: a device powered by a lithium battery if it can accidentally turn itself on, a magnet that can deviate a compass at a distance of seven feet or more than five pounds of dry ice.

To determine if you can ship a specific hazardous item and under what circumstances, Brennan recommends visiting USPS online for more details.

When in doubt, use Long's rule of thumb: “Would I want somebody to send this to me?”

David Arv Bragi is a freelance journalist and marketing consultant. He has been writing about health and safety issues since the 1990s and currently lives in Portland, Oregon.