Neither rain, nor sleet, nor gloom of night will keep the post office from delivering the mail. And neither will chicken scratch.

Each year, the USPS successfully ships over 160 billion packages and letters. Most of that mail—98 percent of it—is swiftly organized by automated sorting machines, which use advanced optical lenses to make out each address. But the machines have their kryptonite. Last year, they failed to read some 2.4 billion pieces of mail—all because of messy handwriting.

If you’re a sloppy scribbler, don’t feel too guilty. Your poor penmanship makes you a job creator! According to The New York Times, more than 700 postal clerks are based in Salt Lake City to decipher America’s most cryptic envelopes. And they mean business. The plant operates 24 hours a day, 365 days a year. Each clerk processes about 20 letters per minute (that’s 1200 an hour!). If a clerk wastes too much time unearthing the address, the letter may get routed to another worker who can do it faster.

How it works

When a sorting machine discovers an illegible letter, it scans it and sends a digital image to the plant in Salt Lake. The image pops onto a worker’s computer. With the help of special software—and a lot of geographical knowhow—the clerk punches in whatever legible letters and numbers they can make out. Through a process of elimination, they keep digging for clues until they find a valid address, which the system confirms. Amazingly, the average clerk can crack the code in just three seconds. (Not everyone can keep up. Twenty percent of new hires quit within five weeks, the Wall Street Journal reports.)

But some letters remain a mystery. Each year, 200 million of the most baffling and awfully penned envelopes are handed down to a team of peek-and-poke clerks, a dying breed of postal worker who sorts mail the old-fashioned way—by hand.

If they can’t translate the slipshod script, the letters are christened “nixies.” The mail is sent to the last line of penmanship gurus, the nixie clerks. If they can’t untangle the meaning behind the scribbles, no one can. The mail may end up in one of two “dead letter offices.” Any valuables get auctioned off, and the correspondence lands a date with the office shredder.