A 29-year-old has this week been arrested over large scale thefts from rural mailboxes in North Canterbury.
The police searched a property near Eyrewell and discovered heaps of opened mail as well as a firearm and ammunition.
"There's a few Grinches out there that are keen to spoil our Christmases," Inspector Brett Callander told RNZ.
"Some of it's opportunistic, you know, sometimes people will just see it and think 'well, that's me' and other times it's actually planned and people are targeting parcels."
The 'planners' can follow parcel trucks around on their routes, he said.
"It can happen anywhere and everywhere, but obviously in rural areas because of the distance and neighbours being further away it's a little bit harder to capture these people."
The thieves do not always know what is in a parcel, but anything electronic would be of value to them, Callander said.
Having a camera on your mailbox can deter people, but it may not actually stop the thefts.
"If you really want to stop your parcels being taken then you might have to send them to a work address or have them click and collect instead of being delivered to your house, or even make sure that you're home when they're going to be delivered.
"Another thing people are doing now is having really clear instructions on where the courier needs to deliver to, that it's hidden and not obvious when it's been delivered."
Cameras can help with the investigation as it did in the Canterbury case, Callander said, and good neighbours were also valuable in solving the case.
"My suggestion is hey, if you're not already a member of your neighbourhood support group then get hold of them and find out how the neighbourhood and the police can work together to stop these Grinches."
If you're going away for Christmas holidays, it's also important to be wary of thieves.
"I don't think you should draw your curtains because that sends a message that nobody's home."
It is better to have a neighbour help keep an eye on your property, perhaps mowing lawns or emptying bins or leaving a car in your driveway to make it look like you're still home.
"Don't put that big 55-inch TV box out besides your rubbish bin because that just screams the fact that you've just got a new TV and that makes it easier for someone to decide that they're going to come and take it."