IPIP Address Lookup
Security & Reputation Scanner

IP Blacklist (DNSBL) Check

Scan any IPv4 address in real time against authoritative spam and malware registries.

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Understanding IP Blacklists and Email Deliverability

Every modern email provider (including Google Workspace, Microsoft 365, Yahoo, and Proton) checks DNSBL registries before accepting SMTP connections. If your server's IP address appears on even one Tier-1 blacklist (such as Spamhaus ZEN), outbound emails will bounce or fail delivery.

Common Causes of Blacklisting

  • Compromised CMS or SMTP Credentials: An outdated WordPress plugin or leaked mail password allows attackers to send bulk pharmaceutical or phishing spam through your server.
  • Open Relays and Proxies: A misconfigured Postfix or Exchange server configured without authentication that forwards arbitrary traffic.
  • Inherited Dirty IP Space: When leasing a new virtual private server (VPS) from a cloud provider (DigitalOcean, Vultr, AWS), the previous tenant may have abused the IP address.

Frequently Asked Questions

What is an IP blacklist (DNSBL / RBL)?▼

A DNS-based Blackhole List (DNSBL) is a real-time registry of IP addresses that have been observed sending spam, running open mail relays, hosting malware, or participating in DDoS botnets. Mail servers and firewalls query DNSBLs in real time to reject abusive connections.

Why is my residential home IP on a blacklist?▼

Many DNSBL lists (such as Spamhaus PBL) intentionally list all residential broadband dynamic IP ranges. This is normal and expected: residential IPs should never run direct mail servers (SMTP port 25). It does not mean your computer is infected.

How do I delist my IP address from Spamhaus or Barracuda?▼

1) Secure your server (remove malware, secure SMTP credentials, close open relays). 2) Visit the provider's official lookup tool (e.g., check.spamhaus.org). 3) Follow the self-service delisting process. Most providers process delisting requests within 1 to 24 hours.

How does this blacklist scanner test lists?▼

This tool performs real-time DNS-over-HTTPS queries against the DNSBL authoritative zones by reversing the IP octets. If the zone returns an NXDOMAIN response, the IP is clean and unlisted. If it returns an A record in the 127.0.0.0/8 range, the IP is actively listed.