Mail Fishing

"Have You Noticed Those Weird New Mailboxes? Here's Why They Changed"

Thieves, often at night, use string to lower glue-covered rodent traps or bottles coated with an adhesive down the chute of a sidewalk mailbox. This bait attaches to the envelopes inside, and the fish in this case — mail containing gift cards, money orders or checks, which can be altered with chemicals and cashed — are reeled out slowly.

This low-tech crime, which became common in the Bronx, is known as mail fishing. 

[In the new mailboxes:] The mail slots are only large enough for letters, meaning sending even small packages will require a trip to the post office. The opening is also equipped with a mechanism that grabs at a letter once inserted, making it difficult to retract. (With an air of crime-fighting secrecy, postal inspectors declined to elaborate on precisely how the device works.)