More than 160,000 people whose names appear on a "suckers list" are to be contacted about how to avoid becoming the victim of a scam.
Details of "repeat victims", who have repeatedly been taken in by scams, are found and then shared by scammers.
Some of those on the list, which covers England, Scotland and Wales, get 60 pieces of mail a day.
People whose names and addresses have been discovered will be contacted by their local authority.
The database of 160,000 people to be contacted has been put together by trading standards teams from a number of sources, including seized lists, names uncovered in the course of investigations and names picked up from actual pieces of mail seized.
Louise Baxter, head of the National Trading Standards scams team said: "Data lists are under-regulated and people don't realise the implications when they tick a consent box on a form".
She said she was "shocked" to find out how scammers use the information they gather.
"There are companies that test people's susceptibility and then generate lead lists.
"You can buy details as specific as people who are 80, disabled, live alone, respond to communication and play the Lottery," she said.
Essex Trading Standards is alerting 2,700 people whose names and addresses are on the list.
The organisation was also given about 200 completed forms with cheques, cash, postal orders, stamps and credit card details - including security codes.
A spokeswoman said: "The money was attached to prize draw applications and orders for confectionery special offers.
"The forms were found in a PO Box used by known scammers."
Anyone who is concerned about a possible scam or is worried about a friend or relative can call the Citizens Advice Consumer Helpline on 03454 04 05 06.