Free DNSBL & IP Blacklist Checker

A DNSBL is a real-time database of IP addresses that have been detected sending spam, compromised by malware, or exhibiting abusive network behavior. Receiving mail servers query DNSBLs via DNS lookups to block or reject messages from listed IPs.

Common triggers include sending emails to spam traps (honeypots), sudden volume spikes without proper IP warmup, sending to unverified purchased mailing lists, compromised user accounts sending malware, or misconfigured open mail relays.

First, diagnose and stop the root cause (e.g. fix compromised credentials or purge invalid email subscribers). Then visit the specific blacklist operator's lookup page (such as Spamhaus or Barracuda) and submit a manual delisting or remediation request.

Spamhaus is used by major ISPs, corporate mail systems, and university networks worldwide. Being listed on the Spamhaus SBL (Spamhaus Block List) or CSS will cause immediate rejection of over 70% of outbound company emails.