DNSBL (Domain Name System-based Blackhole List)

A DNSBL (Domain Name System-based Blackhole List) is a specialized internet service that helps identify and block unwanted or malicious email sources. It maintains a list of domains or IP addresses known for sending spam, phishing, or other harmful content. Mail servers consult these lists during email delivery; if a sender's address appears on the list, the email can be rejected or marked as suspicious. This system improves email security and reduces spam by proactively filtering out problematic sources based on real-time DNS lookups, making communication safer and more reliable.