DNSBL Blacklist Checker

About DNSBL blacklist checker

DNSBL Blacklist Checker tests an IPv4 address against eleven public DNS blocklists, including Spamhaus ZEN, SpamCop, Barracuda and SORBS, and explains what each listing means and how to request removal. It is meant for anyone whose outgoing mail is being rejected or landing in spam.

How to use it

1. Enter a public IPv4 address, such as your mail server's, in the IPv4 address box.
2. Press Check blacklists. Our server queries all eleven lists at the same time.
3. Read the banner for the count of listed and clean results, and whether any list did not answer.
4. Scan the Blacklist results table for each list's zone, status and return code.
5. Open What a listing means for the reason and delisting page of each list you appear on.

How the query is built

198.51.100.25 checked against zen.spamhaus.org

The octets are reversed and a DNS lookup is made for 25.100.51.198.zen.spamhaus.org. A not-found answer means not listed; a 127.0.0.x answer means listed.

When to use it

• Diagnosing sudden bounces from Gmail or Outlook by seeing whether the server IP is listed.
• Checking a new dedicated IP address for prior abuse before you send from it.
• Verifying that a delisting request took effect on every list.
• Screening a shared hosting address before you rely on it for transactional mail.

Questions about DNSBL blacklist checker

What does No answer mean?

That the list refused or could not answer. Several lists, notably Spamhaus, decline queries that arrive through public resolvers, which is how our servers query. It is not a clean result, so try that list from your own mail server.

Are all these lists equally serious?

No. Spamhaus ZEN and Barracuda are widely enforced. SpamCop and PSBL are trap-driven and expire on their own. UCEPROTECT Level 1 is aggressive and many receivers ignore it. The meaning text explains each.

Why can I not check an IPv6 address?

Most of these lists publish IPv4 zones only, so IPv6 input is rejected with a message. Private, loopback and reserved IPv4 ranges are also refused, since blocklists only track public addresses.

Does being listed prove my server is compromised?

Not necessarily. Causes include a compromised mailbox, a shared IP with a noisy neighbor, a spam-trap hit or a previous owner's abuse. Find the cause first, then request delisting.

How is the request limited?

Each check sends eleven DNS queries, so it is limited to 5 checks per minute. The IP address is sent to our server, which makes all the queries.

Related tools

• MX record lookupLook up a domain's MX records, resolve each mail host to its IP addresses, and flag delivery-breaking misconfigurations.
• IP LookupLook up information about an IP address
• DNS LookupLook up DNS records for a domain
• WHOIS LookupLook up WHOIS information for a domain
• PingPing a domain or IP address
• SSL LookupLook up SSL certificate information for a domain