What is a DNSBL (DNS Blackhole List)?
A Domain Name System Blackhole List (DNSBL) is a database of IP addresses that have been flagged for sending spam, hosting malware, or participating in botnets. Email servers use these lists to reject messages from untrusted sources.
Our tool performs a real-time DNS query against Spamhaus ZEN, one of the internet's most comprehensive and widely used IP reputation databases. If your IP is listed, your emails will likely bounce or end up in the recipient's spam folder.