Page "Email authentication" Paragraph 9

So called policy lists are blacklists that contain IP addresses on a preventive basis.

An IP address can be listed therein even if no spam has ever been sent from it, because it has been variously classified as a dial-up address, end-user address, or residential address, with no formal definition of such classification schemes.

Not requiring evidence of spam for each listed address, these lists can collect a greater number of addresses and thus block more spam.

However, the policies devised are not authoritative, since they have not been issued by the legitimate user of an IP address, and the resulting lists are therefore not universally accepted.