An investigation has been launched following the discovery of 40,000 items of undelivered mail at a recycling plant in the Swansea Valley.
The Royal Mail said a former-postman is helping with inquiries
They were found by workers sorting through skips delivered to a recycling company near Ystradgynlais.
The Royal Mail, which is conducting an inquiry, said there were 3,000 letters and the rest were items such as door to door leaflets.
A spokesman said a former postman was helping with internal inquiries.
The skips were ordered from the JLA Recycling plant.
Company director John Adams told the BBC Wales news website: "A local man in Ystradgynlais ordered a skip and when it came back there was quite a large number of bulk mail items.
"He ordered another skip and this time there was a very large quantity of personally addressed mail."
He said they called the police. In the meantime the man ordered a third skip and when it was returned it included a large quantity of Royal Mail bags, a garden incinerator and items of semi-burnt mail.
Mr Adams said officials from the Royal Mail's special investigation branch attended.
"I think they were very shocked at the amount there was," he said.
"It took three vans to take it all away."
A Royal Mail spokesman said such incidents were rare and only 0.006% of the annual 22 billion items it delivered nationally was lost or stolen.
"Our internal investigations team are currently conducting inquiries into the incident and we will be re-delivering as much recoverable mail as soon as possible," he added.
"We apologise to customers whose mail deliveries will have been affected and we would emphasise that every single item of mail is important to us.
"We operate a zero tolerance policy towards any failure to deliver mail by any of our postmen and women."