A how-to is an informal, often short, description of how to accomplish a specific task. A how-to is usually meant to help non-experts, may leave out details that are only important to experts, and may also be greatly simplified from an overall discussion of the topic.
A DNS-based Blackhole List (DNSBL) or Real-time Blackhole List (RBL) is an effort to stop email spamming. It is a “blacklist” of locations on the Internet reputed to send email …