"We are investigating these crimes and we will arrest these individuals and bring them to justice," Harris said.
She said they're also replacing and retrofitting mailboxes to make them fishing-resistant.
"Crime trends change and you have to change with them to maintain your relevancy," Harris said.
How to keep your mail safe:
Deposit your mail before the last collection time, said Harris. This will prevent your mail from sitting in the box overnight, she said, when mail fishers most often come out. (On most mailboxes, you'll see a list of the pick-up times).
McCleskey took it a step further.
"Take your mail and put it in the post office, and when I say in the post office, I mean walk in and put it in, which is kind of a pain but I've seen mail stolen directly out of the receptacles outside as well," he said.
Consider requesting a number for your mail and following it, he added.
"I would highly recommend tracking your mail right now," he said.
The New York City Police Department recommends using a pen with pigmented (permanent) ink to write checks out, as it's harder to wash away.
You also want to check your account balance frequently to make sure your checks were cleared by the establishments that you wrote them to, according to the NYPD. Contact your bank as soon as you realize something is amiss.
Harris said people should also call the United States Postal Inspection Service at 877-876-2455, so it can investigate.
"If they see someone committing a crime against the blue box, call 911 immediately," said Harris.