Since we put our house on the market a few months ago we've been getting regular items of unsolicited mail, addressed to "the homeowner". They come from surveyors, removals companies, storage companies and estate agencies (who ususually tell us exactly how many days our house has been on the market in the hope that we'll switch to them instead). These companies always have addresses in other parts of the country, suggesting that they're larger firms that operate nationally (for example 'Your Move' is one of the biggest culprits).
They can't be directly mining the address data from Rightmove/Zoopla because that only gives a postcode. So would it be reasonable to assume they're all buying access to a database of addresses? If so, who is compiling the database? Do they have people driving down streets where they know houses are listed, to get the house numbers? Or perhaps all the estate agencies are on some sort of commission to pass addresses on (surely a GDPR breach if so)?