When one of the registrars sends an addition, deletion or modification to a DNS record, SnapNames receives a copy of that change and maintains its own comprehensive database of domain name registrations called Whois.
By combining its existing 1m names (gathered from people who had responded to previous offers on tinned goods) with lists of similar households bought from brokers, Heinz has built up a database of 4.6m people to send a copy of At Home, a free magazine of recipes which also promotes its products.
Among the first to go were Metromail, a direct-mail-database company, and Donnelley Enterprise Solutions, which ran copy departments and mail rooms for law firms and the like.