Why check if your IP is blacklisted?
A blacklisted IP address means your emails will be rejected or marked as spam by major providers (Gmail, Outlook, Yahoo). IP blacklists, also known as DNSBLs (DNS-based Blackhole Lists) or RBLs (Realtime Blackhole Lists), are queried by mail servers before accepting an email.
Impact of a blacklisted IP:
- Rejected emails (bounce) with "550 blocked" or similar messages
- Emails in spam even with correct SPF, DKIM, and DMARC
- Damaged reputation that can persist even after delisting
Three reasons to check regularly:
- Detect a problem before your customers report it
- Identify a compromised server sending spam without your knowledge
- Verify a new IP before using it in production
How does a DNSBL check work?
When you send an email, the receiving server can check your IP against blacklists via a reverse DNS query:
# To check 192.0.2.1 on Spamhaus ZEN:
dig A 1.2.0.192.zen.spamhaus.org
# Response if listed:
127.0.0.2 → SBL (direct spam)
127.0.0.4 → XBL (compromised IP)
127.0.0.10 → PBL (dynamic/residential IP)
# Response if clean:
NXDOMAIN (no response = not listed)
Our tool performs this check on 25+ lists simultaneously and interprets the return codes to give you a clear diagnosis.
Blacklists checked by the tool
Tier 1 - Critical (used by Gmail, Outlook, Yahoo)
| Blacklist | DNS Zone | Impact |
|---|---|---|
| Spamhaus SBL | sbl.spamhaus.org | Confirmed spammers - Critical impact |
| Spamhaus XBL | xbl.spamhaus.org | Compromised IPs/botnets - Critical impact |
| Spamhaus PBL | pbl.spamhaus.org | Dynamic IPs (policy) - Moderate impact |
| Spamhaus ZEN | zen.spamhaus.org | Combined SBL+XBL+PBL |
| Barracuda BRBL | b.barracudacentral.org | Barracuda reputation - Critical impact |
| SpamCop | bl.spamcop.net | User reports - Auto-delist 24-48h |
Tier 2 - Important
| Blacklist | DNS Zone | Impact |
|---|---|---|
| SORBS | dnsbl.sorbs.net | Spam and open relays |
| UCEProtect L1 | dnsbl-1.uceprotect.net | Individual IPs |
| UCEProtect L2 | dnsbl-2.uceprotect.net | IP ranges |
| PSBL | psbl.surriel.com | Passive spam block |
Tier 3 - Additional
Mailspike, SpamRATS, JustSpam, WPBL, and other regional or specialized lists.
Understanding your reputation score
| Score | Grade | Meaning | Action |
|---|---|---|---|
| 95-100 | A+ | IP clean on all lists | No action required |
| 85-94 | A | Minor listings | Monitor, delisting optional |
| 70-84 | B | Tier 2 listings | Request delisting |
| 50-69 | C | Tier 1 listings | Urgent action required |
| 30-49 | D | Multiple critical listings | Priority delisting |
| 0-29 | F | Severely compromised IP | Consider changing IP |
Real-world diagnostic cases
Case 1: IP listed on Spamhaus SBL
Symptom: Emails rejected with "550 5.7.1 blocked using Spamhaus"
Diagnosis:
- Spamhaus SBL = confirmed spam source
- Critical impact on deliverability
Actions:
- Identify the cause (compromised server, exploited web form, malicious user)
- Fix the problem at the source
- Request delisting via Spamhaus SBL Removal
- Timeframe: 24-48h after the fix
Case 2: IP listed on SpamCop only
Symptom: Some emails in spam, no mass rejection
Diagnosis:
- SpamCop = recent user reports
- Moderate impact, auto-delisting in 24-48h
Actions:
- Check logs to identify reported emails
- Wait 24-48h without sending spam
- The IP will be automatically removed if no new reports
Case 3: IP listed on PBL (Policy Block List)
Symptom: Emails rejected, but the IP has never sent spam
Diagnosis:
- PBL = IP classified as "shouldn't send emails"
- Often residential or dynamic IPs
Actions:
- If legitimate mail server IP: request removal via Spamhaus PBL Removal
- If residential IP: use your ISP's SMTP relay or a third-party service
FAQ - Frequently asked questions
Q: How do I know if my IP address is blacklisted?
A: Enter your IP address in the tool above and click 'Check'. In 10 seconds, you'll know if your IP is listed on any of the 25+ major blacklists. A reputation score (0-100) and grade (A+ to F) show your IP's overall status.
Q: Why is my IP on a blacklist?
A: Common causes: sending spam (intentionally or via compromised server), open relay, dynamic IP, or inherited reputation. Spamhaus PBL lists residential IPs by policy, which isn't an accusation of spam.
Q: How do I remove my IP from a blacklist?
A: Each blacklist has its own procedure. Our tool provides direct links. Spamhaus: 24-48h after request. SpamCop: auto-delist in 24-48h. Barracuda: manual request required.
Q: Which blacklists are the most important?
A: Tier 1 (critical): Spamhaus, Barracuda, SpamCop. Used by Gmail, Outlook, Yahoo. Being listed on these severely impacts your deliverability.
Q: What's the difference between IP blacklist and domain blacklist?
A: DNSBL (IP) = addresses of spamming servers. URIBL/SURBL (domain) = domains in spam content. Test both for a complete diagnosis.
Q: How often should I check?
A: After every server/IP change. For routine monitoring: weekly or monthly. Immediately if emails are rejected or landing in spam.
Q: My IP is on PBL, is that serious?
A: Not necessarily. The PBL lists IPs that shouldn't send emails directly (residential, dynamic). If you have a legitimate server on a static IP, request removal.
Complementary tools
| Tool | Purpose |
|---|---|
| Domain blacklist checker | Check if your domain is on a URIBL/SURBL |
| Email tester | Complete deliverability test with score |
| Domain email audit | Check your domain's SPF, DKIM, DMARC |
| Header analyzer | Diagnose a rejected or spam-flagged email |
| SPF inspector | Check your SPF record |
Useful resources
- Spamhaus - How to request delisting (official procedures)
- Barracuda Central - Reputation Lookup (verification and delisting)
- RFC 5782 - DNS Blacklists and Whitelists (DNSBL technical specification)
- Google - Email sender guidelines (Gmail requirements)