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Blacklist & Reputation Checker
Check IP and domain status across DNSBL, URIBL, and mail reputation services.
Check whether an IP address or domain appears on common DNSBL/RBL blacklists.
Blacklist Results for
DNS Blacklists (DNSBL): How They Work
A DNS-based blacklist is a DNS zone where each entry is an IP address encoded as a domain name. To check if IP 1.2.3.4 is listed on zen.spamhaus.org, a mail server queries 4.3.2.1.zen.spamhaus.org via DNS. If the query returns an answer (usually 127.0.0.x where x encodes the listing reason), the IP is listed. If it returns NXDOMAIN, the IP is clean.
| Blacklist | Scope | Impact if Listed |
|---|---|---|
| Spamhaus ZEN | Combined SBL (spam), XBL (botnets), PBL (dynamic IPs). Most widely used. | Major providers reject mail. 80%+ of spam filtering references Spamhaus. |
| Barracuda BRBL | Barracuda Networks reputation list. Free for low-volume use. | Barracuda appliances and cloud service users reject mail. |
| SpamCop SCBL | Crowd-sourced spam reports. Entries expire automatically after 24 hours without new reports. | Moderate impact. Many smaller providers use SpamCop. |
| SURBL / URIBL | Lists domains found in spam messages, not sending IPs. | Affects links in emails. Even if your mail passes, your links may be blocked. |
| Microsoft SNDS | Outlook/Hotmail/Exchange Online internal reputation (not a public DNSBL). | Delivery to Microsoft-hosted mailboxes. Requires SNDS account to query. |
How IPs Get Blacklisted & How to Delist
Common Reasons for Listing
- Your server or a neighbor on the same IP range sent spam
- Compromised web form sending spam through your mail server
- Open SMTP relay misconfiguration
- IP was previously used by a spammer (history follows the IP)
- Malware infection sending spam from a client machine behind your IP
Delisting Process
- Identify the cause: Check mail logs for unusual outbound volume. Fix the root problem first or you will be relisted.
- Spamhaus: Use their Blocklist Removal Center at spamhaus.org. Free for most listings. Provide a clear explanation of the issue and fix.
- Barracuda: Submit removal request at barracudacentral.org/rbl/removal-request. No account needed for basic removal.
- Microsoft: Use SNDS (sendersupport.olc.protection.outlook.com/snds). Requires a Microsoft account and Junk Mail Reporting Program signup.
5 Blacklist Prevention Tips
1. SPF + DKIM + DMARC: Proper email authentication prevents spoofing of your domain. The majority of spam that causes blacklisting comes from forged sender addresses.
2. Rate limit outbound mail: Limit to 100-500 recipients per hour per account. Sudden spikes in outbound volume are a strong spam signal.
3. Monitor blacklist status: Automated monitoring catches listings before customers notice delivery failures. Check daily for critical mail servers.
4. Secure web forms: Add CAPTCHA and rate limiting to contact forms. Compromised forms are the #1 source of spam from legitimate servers.
CLI Equivalent
# Check Spamhaus (reverse IP notation)
dig +short 4.3.2.1.zen.spamhaus.org
# Check Barracuda
dig +short 4.3.2.1.b.barracudacentral.org
# Check SpamCop
dig +short 4.3.2.1.bl.spamcop.net