"So just a quick little thank you for leaving me the opportunity of stealing your package. Very nice of you," the person wrote.
They even signed the letter off as: "The new owner of your package".
St Paul Police Department, who believed the thief's act was unbelievable, shared a photo of the note and warned residents to take extra care when expecting deliveries.
"Porch pirates are the scourge of the holiday season, creeping around neighbourhoods at all hours of the day, tip-toeing up to homes, stealing packages that don't belong to them," they warned.
New Zealand Post told the Herald how Kiwis can keep their parcels secure during the Christmas period.
"NZ Post is proud to have a range of secure delivery options available to help keep your Christmas parcels safe and sound. We're pleased to offer customers the ability to have parcels directed to one of our almost 300 parcel collect locations – including Countdown supermarkets.
"Customers can also text us to redirect delivery if you get held up and aren't going to be home in time to collect it. Customers can even tell us the exact spot where you want us to leave your parcel, for example 'on the back porch under the BBQ cover' and our delivery people will make sure it's safely tucked away. You can find out more on our website www.nzpost.co.nz."