"The operator team of the SURBL anti-spam blacklist have announced a far-reaching change to the usage policy. While the use of the project’s DNS server has been free so far, the list’s operators are now demanding a usage fee from service providers that offer spam filter services for more than 1,000 mailboxes or 250,000 emails per day.
These service providers are now required to subscribe to a sponsored data service, which will include direct access to SURBL data, as well as support. The funds will be used to ensure the quality and accessibility of the service." – Content courtesy of SURBL anti-spam blacklist to be a paid service – News – heise Security UK