More than 200 postal scams were reported during a week-long crack down involving Belper library.
Derbyshire County Council ran a Scamnesty week during May – encouraging residents to hand in suspect letters.
County council trading standards officers have now analysed the information which helps them target their future enquiries.
The top five mail scams were prize draws, inheritance scams, health products, foreign lottery scams and clairvoyants.
Emma Hagger, from Amber Valley Citizens’ Advice Bureau, said: “Scammers are growing increasingly sophisticated and it can be easy to be taken in.”