NetworkWhois - Free network diagnostic tools

IP Blacklist Checker - Check Major Spam & Email Blacklists

Our free IP blacklist checker scans an IP address against major spam databases (DNSBL/RBL) to help you diagnose email deliverability problems. When a sending IP is listed, providers like Gmail and Microsoft can reject your messages or place them in spam. Use this tool to check a single IP, CIDR, or small range (up to 256 IPs), see which lists flagged you, and then follow delisting guidance after you fix the root cause.

Check IP Reputation

Supports: Single IP • IP ranges • CIDR
Note: Maximum 256 IPs per request.

Blacklist Checks

Spamhaus ZEN, Barracuda, SpamCop, and UCEPROTECT levels 1–3

Range Support

Check CIDR ranges and IP ranges up to 256 IPs per request

Instant Results

Real-time DNSBL queries from our servers

Blacklists we check

  • Spamhaus ZEN (SBL/XBL/PBL composite)
  • Barracuda (Barracuda Reputation Block List)
  • SpamCop (SpamCop Blocking List)
  • UCEPROTECT L1 (individual IPs)
  • UCEPROTECT L2 (network ranges)
  • UCEPROTECT L3 (ASN-level)

How to use the IP blacklist checker

  1. Enter an IP address (or CIDR/range) used for sending email.
  2. Click “Check Blacklists”.
  3. Prioritize fixing critical listings first (especially Spamhaus).
  4. If you don’t know the sending IP, find your mail server via DNS Records Lookup and verify ownership via IP WHOIS Lookup.

How blacklisting impacts email delivery

Blacklists can cause two common outcomes: hard bounces (SMTP rejection) or spam-folder placement. If you’re troubleshooting deliverability, also validate SPF/DKIM/DMARC and PTR records, and test your setup with Email Validator.

Delisting checklist

  • Stop outbound spam: check mail logs, queues, and compromised accounts.
  • Fix open relay and require SMTP auth for submission ports.
  • Harden the server (patch OS/apps, strong passwords, 2FA where possible).
  • Confirm reverse DNS (PTR) is configured using Reverse DNS Lookup and generate PTR syntax using PTR Record Generator.
  • Request delisting from the specific provider (or wait for auto-expiry where applicable).
  • Recheck until clean, then warm up sending volume gradually.

Common Questions

What is an IP blacklist (DNSBL/RBL)?

IP blacklists are spam and abuse databases used by mail servers and security systems. If your sending IP is listed, your emails may be rejected or filtered to spam.

How does blacklisting affect email deliverability?

Major providers use reputation signals. A listed IP can cause SMTP rejections (hard bounces) or spam-folder placement, especially for transactional email and newsletters.

Why do IPs get blacklisted?

Common causes include compromised servers/accounts sending spam, open relay configuration, poor list hygiene, high complaint rates, or sending from dynamic/residential IP ranges.

How do I get delisted?

First fix the root cause (stop spam, secure the server, fix relays). Then follow the blacklist’s delisting process (some auto-expire, others require a request). Recheck after changes to confirm removal.

Should I check a domain or an IP?

For email deliverability, check the outbound sending IP of your mail server. If you’re unsure, look up your MX host and resolve it to an IP with a DNS records lookup.

What if I'm listed only on UCEPROTECT Level 2/3?

Level 2/3 can indicate your provider range or ASN is flagged, sometimes due to neighbors. Consider using a cleaner sending IP, tightening outbound policies, or contacting your provider.

Related tools