A pedestrian walks past a U. S. Postal Service mailbox in New York. Timothy Fadek | Bloomberg | Getty Images

It was around noon on April 12. Josefina Gomez Pando, 83, dropped a check for $112 into a blue mailbox on a corner on the Upper West Side of Manhattan. Then she proceeded to her doctor's appointment. Her check would never make it to the mailman. That's because someone else, most likely using a sticky rat trap attached to the end of a string, fished her check right back out of that mailbox.

And then they wrote a new one for $3,500. "I pay all my bills by mail — around 30 checks a month," said Pando, who owns three buildings in New York City. "This never happened to me."

Mailboxes increasingly are a target for criminals

"Mail fishing" is when people use tools to retrieve envelopes out of the blue mailboxes lining the streets, and it's on the rise, according to law enforcement officials. "It's doubled over the last two years, at least," said Lt. John Grimpel, a spokesman for the New York City Police Department. There were 2,800 complaints of mail fishing filed across the five boroughs of New York in 2017, and 1,300 submitted so far this year, he said. Mail fishers are not unique to Manhattan, however. Mail is under siege in Texas, Florida, New Jersey, Massachusetts, Colorado and California, among other places. "It's coast to coast," Grimpel said. The increase in mail fishing can be blamed in part on how the world is growing more complicated, said R. Sean McCleskey, a retired United States Secret Service agent who supervised an identity theft task force for more than a decade.

Always when I make my signature, I make a line under my name, and this signature that has been falsified has no line. Josefina Gomez Pando a victim of mail fishing

"The more companies are hardening up their policies on their cybersecurity, [criminals] might say 'I don't have the skill level to break into a computer now, but I can sure as heck go to the mailbox,'" McCleskey said. Even as more communications and payments play out on screens, nearly 150 billion pieces of mail were sent out in the United States in 2017.

Trying to find recourse

Two days after Pando left her check in the mailbox, she received a call from Citibank. "They said they need to talk with me," Pando said. She stopped by her nearest branch, where she was told she might have been a victim of fraud. When she saw the check, she was taken aback. "It was very good writing and it was very professional writing," Pando said.

But the signature on the check was clearly not hers. "Always when I make my signature, I make a line under my name," she said. "And this signature that has been falsified has no line." The bank did not allow Pando's check to clear. More from Personal Finance:

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3 ways to get other people to pay off your student loan "At Citibank, we take check fraud very seriously and we maintain regular contact with local police as part of our aggressive strategy to combat all types of fraud," said Drew Benson, a spokesman for the company. Paul Benda, senior vice president of risk management policy at the American Bankers Association, said it's seeing an uptick in mail fishing but that banks deploy sophisticated algorithms to detect such suspicious transactions. "There's really a comprehensive system to stop this fraud," Benda said. Donna Harris, a spokeswoman for the New York division of the United States Postal Inspection Service — the Postal Service's law enforcement division — declined to comment on the dollar amount stolen each year through the mail.

Someone breaking into your mail, just as bad as a computer

So how do these people break into the boxes? Unless your arm is plastic, you can't get your hand in the mailbox, said Grimpel of the NYPD, adding that they usually send those rectangular sticky traps that people use to catch rodents down the mailbox slots, with a string. They can pull up 20 envelopes at a time this way, he said. Mail fishers have other techniques, as well. "I've seen more traps that I can tell you," said McCleskey. "I've seen them roll up and put a chain around the mailbox and drag it down the street." While not all endeavors to steal mail are fruitful — "every time you go fishing," Grimpel said, "you don't catch a fish" — plenty of times, they are.

Criminals can get their hands on people's gift cards, cash-filled birthday greetings, rent checks, money orders, credit cards or documents with home addresses and Social Security numbers. "You can basically build a profile of an individual from the information you gather in the mail," McCleskey said. And as was done to Pando, thieves can "wash" a person's check of ink with easy-to-buy chemicals. Then they have a blank check with which to do whatever they want.

Trust in the mail takes a hit

Mail theft is a federal crime, and can land someone in prison for up to five years. The police have been trying to catch these thieves, by hiding cameras near the blue boxes and staking them out in the middle of the night when the criminals most often go fishing. "If they observe them sticking a glue trap down the mailbox, that's probable cause they're not mailing a letter," the NYPD's Grimpel said. The United States Postal Inspection Service is also on the case.

This is a bad thing because many people depend on the mail. Josefina Gomez Pando a victim of mail fishing