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.