The report also revealed that consumers who prefer a combination of online and direct mail spend on average £105 a month on goods and services. This is £19 more than those who prefer just online ads, and £34 more than consumers preferring only direct mail.
Anthony Miller, head of media development at Royal Mail, said: "It is important that companies take notice of consumers' feelings about spam as it is turning them off to a point where it could undermine the benefits of digital as a communications tool.
"Companies who understand how their customers want to be communicated with will benefit through increased sales and loyalty."
Another compelling argument for the use of combined online and DM comes from Royal Mail's discovery that over half of those surveyed believe that DM gives a better impression of a company than email. Also 69% feel that email is best used for supporting or clarifying the mail they receive.
Miller said: "Consumers recognise the benefits of online, email and direct mail for different types of communications and how they work well together."