IP Blacklist Checker

What are Email Blacklists?

Email blacklists (also called DNS-based Blocklists or DNSBLs) are real-time databases of IP addresses known or suspected of sending spam, malware, or other unwanted email. When a mail server receives an email, it checks the sender's IP address against one or more DNSBLs. If the IP is listed, the email may be rejected, marked as spam, or quarantined — depending on the receiving mail server's policy.

Blacklists Checked

• Spamhaus ZEN — The most widely used and respected blacklist. ZEN combines the SBL (Spamhaus Block List), XBL (Exploits Block List), and PBL (Policy Block List). Being listed here has the most severe impact on email deliverability.
• SpamCop BL — Based on spam reports submitted by users and traps. Listings are typically short-lived (24-48 hours) as they expire if no new reports come in.
• SORBS DNSBL — The Spam and Open Relay Blocking System maintains several sub-lists covering spam sources, open relays, open proxies, and dynamic IP ranges.
• Barracuda Reputation — Maintained by Barracuda Networks, used by their email filtering appliances. Based on Barracuda's own spam trap network.
• UCEPROTECT Level 1 — Lists individual IPs that have been caught sending spam. Levels 2 and 3 are more aggressive, listing entire network ranges.
• PSBL (Passive Spam Block List) — A conservative list maintained by Surriel.com. Listings are typically quick to expire once spam stops.
• CBL (Composite Block List) — Focuses specifically on IPs showing evidence of spam bot infection, open proxy abuse, and malware-based spam.
• ix.dnsbl.manitu — A German DNSBL that lists IPs sending spam to their network of spam traps.

What to Do If You're Listed

• Identify the source — If your IP is sending spam, first identify whether your server has been compromised, has an open relay, or if a legitimate user is sending spam through it.
• Secure your server — Close open relays, update your mail server software, reset compromised accounts, and scan for malware.
• Request delisting — Each DNSBL has its own delisting process. Spamhaus has an online lookup and removal request form. SpamCop listings expire automatically. For others, visit their website for removal instructions.
• Implement email authentication — Set up SPF, DKIM, and DMARC records to prevent your domain from being spoofed, which can lead to blacklisting.
• Use a dedicated sending IP — If you send marketing emails, use a dedicated IP or an email sending service (Mailgun, SendGrid, etc.) with a clean reputation.

How DNSBL Checking Works

DNSBL checks work by reversing the IP address and prepending it to the DNSBL domain, then performing a standard DNS A record lookup. For example, to check if 1.2.3.4 is listed in zen.spamhaus.org, the query is made for 4.3.2.1.zen.spamhaus.org. If an A record is returned (usually in the 127.0.0.x range), the IP is listed. If the result is NXDOMAIN (no record), the IP is clean.

This tool performs all 8 checks simultaneously using Cloudflare's DNS over HTTPS API, giving you complete results in just a few seconds. The returned A record value (if listed) can sometimes indicate the reason for listing — for example, Spamhaus returns different IP addresses to indicate whether the listing is from the SBL, XBL, or PBL sub-list.

Email Deliverability Best Practices

• Set up a valid PTR (reverse DNS) record for your mail server's IP
• Publish an SPF record in your domain's DNS
• Sign outgoing emails with DKIM
• Implement a DMARC policy (start with p=none, then move to p=quarantine or p=reject)
• Monitor your IP reputation regularly using tools like this one
• Use a separate IP or subdomain for transactional vs. marketing emails
• Maintain clean email lists and handle bounces and unsubscribes promptly