Police have intercepted more than 18,000 fraudulent scratch-and-win letters at the border, sent from international scammers looking to rip off New Zealanders.
The dodgy letters have been coming to New Zealand since at least 2013, and include a scratch-and-win ticket.
Police say the letters are coming from Malaysia.
Recipients "win" more than US$150,000 and have to contact the company to arrange getting their prize.
They are told they must pay money to "release" their prize, including local taxes and legal, insurance and court fees to "prove the money is not from illicit offending".
In the past Kiwi victims have been fleeced for more than $1.7 million.
READ MORE: The $1.7m Malaysia-based scratchie scam
Detective Senior Sergeant Aaron Pascoe said police teamed up with NZ Post several months ago to intercept the letters as they came into the country.
"We were looking at the envelopes and the consistent way the offenders were doing them," he told the Herald.
"They were unique, so we came up with a production order so that NZ Post could produce all envelopes coming through the border that matched the description."
Pascoe said more than 18,000 envelopes have been intercepted so far.
The offenders must have realised that authorities here were onto them though, as they were now sending the scam mail differently.
Instead of plain white envelopes with printed labels, the scammers were now using multi-coloured stationery and handwriting names and addresses.
"Unfortunately, they worked out another way to change it up. It's still happening, but we managed to stop 18,000 letters reaching potential victims."
He said the number of victims approaching police had all but stopped since the interception began.
This week he heard of one person who had contacted Netsafe claiming to have lost around $64,000 in the scam. That person was yet to contact police.
Pascoe urged people to be sensible when it came to unsolicited mail competitions and prizes.
"If it sounds too good to be true - it probably is," he said.
In 2013 a victim of the scam spoke to the Herald about her loss.
She paid $18,000 to "release" her prize of US$170,000.
Over the next two weeks she spoke to two men from the company about collecting her prize and they managed to convince her to send them money.
"Foolishly I believed them ... Foolishly, also, I ignored the warning on the Western Union form about not sending money to people one didn't know personally," she said at the time.
The Department of Internal Affairs said many people were fooled by scams as they looked genuine.
They said sure signs of a scam included getting unsolicited letters advising the recipient had to "act fast" to claim money or some other prize in a lottery or competition that they had not entered.
"If you're not sure, don't respond," the agency advised.
Keeping pests out of the post
The police and NZ Post are not the only authorities stopping pests at the border.
The Ministry for Primary Industries 2015/16 mail compliance monitoring survey showed 99.93 percent of arriving international letters, parcels and other mail items were clear of biosecurity risk.
The survey involved mail inspections that took place after the items had passed through biosecurity controls such as detector dog and x-ray screening at the International Mail Centre in Auckland.
More than 1.6 million items were processed at the mail centre during the survey period between 16 and 29 May.
MPI inspected 4367 mail items for the survey and found just five non-compliant risk goods including seeds, a partly dried leaf with fungal growth and meat in homemade cans.