Not email, paper mail:
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.
In response, the US Post Office is introducing a more secure mailbox:
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.
The crime has become more common in the past few years.