Birthday cards, often with cash inside, are going missing and allegedly being stolen in Penarth, an ITV investigation has found.
Mum-of-two Rhian Evans, who lives in the Vale of Glamorgan town, said she first noticed her post was going missing over the summer.
She said relatives sent her sons birthday cards with money inside - but some did not arrive.
When she inquired about it in the town, she realised many others were experiencing missing mail too.
There are now calls for an investigation.
Rhian said: "It was my eldest son’s birthday in May, and I noticed that he had fewer cards from relatives than he’d normally have. We enquired with relatives and they said they’re sent cards with money in them and they’d just never turned up.
"We waited a few weeks and nothing arrived. At the time, I thought maybe it was just one of those things, they’d maybe got lost in the post.
"A month later, it was my second son’s birthday and the same thing happened again. None of the cards or money arrived.
"It would have been around maybe £20 in each card so probably about £40 to £60 went missing altogether for each of them, so that would amount to about £120."
She complained to Royal Mail and was told standard first and second-class items aren’t tracked so the matter could not be investigated further. It is not known what happened and how the cards went missing.
But she knew others had experienced similar issues so decided to share what had happened on a community Facebook group, and was overwhelmed with the response.
"I was bombarded with messages,” she said. "I received tens and tens of comments by people in the local area saying that money and cards were going missing, particularly birthday cards and some were arriving opened and things taken out of them."
Among the comments on Facebook, people in the area claimed:
"We've had money taken from cards and post ripped or partially opened."
"I had envelopes stolen that contained ten pounds each - they were for children."
"I've had cards missing since last November - all containing money."
"I made a complaint as we had vouchers and cash taken from birthday cards."
Royal Mail said they'd investigate and sent me some stamps as compensation."
Rhian and others in the town are now calling for an investigation into the postal system.
"I’m sure our town is not the only town this is happening in, they need to act on it now," Rhian said.
ITV Wales investigation
To investigate the issue further, ITV Wales sent eight colourful birthday cards from various locations. Four of the cards contained £5 notes.
Seven out of eight cards arrived at their intended destination, including the cards containing money, but two looked damaged and one card went missing completely.
Two birthday cards appeared damaged when they arrived.
Credit: ITV Cymru Wales
Royal Mail declined an interview but a spokesperson said: "We acknowledge the results of ITV Wales’ own investigation that confirmed all letters containing money arrived as intended.
"The process for delivering the millions of letters that arrive everyday involves an entire network of letter drums and sorting machines which can occasionally result in clipping or minor damage to the envelope as shown in their examples.
"We publish guidance online for sending valuables, this includes sending letters via special delivery, measures such as packing any money securely to make it invisible from the outside and not indicating on the packaging that money is enclosed.
"We take the security of mail very seriously and investigate any concerns raised by customers."