More than 1000 letters or packages sent through New Zealand Post are reported lost in the mail every week, and the service has paid more than $450,000 to affected customers in the past year.
Figures obtained by the Herald show 55,087 reported cases of undelivered mail, 6045 more than the year before. Of those, 678 were cheques.
NZ Post paid $452,235.62 to 5580 customers - including for 20 of the missing cheques - who did not receive mail, according to figures received under the Official Information Act.
NZ Post said the cases were initially logged with its customer service centre but sometimes items were eventually delivered or found so it was unable to give accurate figures on how many were traced and how many were never seen again.
A spokeswoman for the service said 834.5 million items were delivered in the year to June 30, an average of 16 million a week.
One letter in every 15,000 went missing - .007 per sent of the total mail volume, she said.
"Your request provided a really interesting insight into the common excuse that the cheque someone was supposed to send must have got lost in the mail. The figures show that the next time people hear that line, they're entitled to feel at least a bit sceptical.
"As with any postal service worldwide, a small proportion of items sent will go astray from time to time.
"There are a multitude of reasons why this occurs - including incorrect addressing, incorrect postage, and in rare instances negligence.
"While we are not able to track the outcomes of all reports, it is fair to say that most will have been resolved reasonably simply - through the cheque subsequently arriving, or by cancelling the cheque and sending a replacement."
Paul Ford, a spokesman for online bidding site Trade Me, which sells about 40,000 items a day, said shipping and lost parcels were regular topics on its message boards.
He advised buyers and sellers to do their research when choosing a postal service.
"It's a competitive market. If you don't have a great experience with shipping provider number one, then go for number two. There are lots of different services from a bunch of different providers.
"If you're posting valuable items, make sure you are covered by choosing a track-and-trace option just in case something goes wrong."
Clothing retailer EziBuy, which distributes up to 20,000 items a day to 1.5 million customers in New Zealand and Australia, said its customers hadn't reported feedback on missing mail.
"Our own internal seeding of addresses - where we test service provided by post - reflects a high level of service in terms of on-time, accurate delivery," said chief executive Simon West.
MISSING POST (by NZ Post in the year to Jun 30)
* 55,087 mail items reported missing.
* 6045 more than the year before.
* 1059 items missing a week.
* 678 cheques missing.
* $452,235.62 paid to customers for missing mail.