IP Blacklist Lookup: How to Tell If You’ve Been Blocked

If your emails have suddenly stopped reaching inboxes—or worse, aren’t being delivered at all—your IP address may be on a blacklist. And when that happens, your email deliverability can plummet overnight.

In this guide, you’ll learn:

• What an IP blacklist is
  
• How to check if your IP is listed
  
• The tools to use for a blacklist lookup
  
• What to do if you’ve been blocked
  

What Is an IP Blacklist?

An IP blacklist is a database used by spam filters and mailbox providers to block mail from IP addresses known (or suspected) to send spam.

When your sending IP appears on a blacklist, your emails may:

• Be rejected outright with SMTP error codes (like 550 5.7.1)
  
• Go straight to the junk folder
  
• Be silently discarded (no bounce, no warning)
  

These lists are maintained by organizations like Spamhaus, SORBS, and Barracuda, among others.

Common Signs You’ve Been Blacklisted

You might be on a blacklist if you notice:

• A sudden drop in open or click-through rates
  
• Emails not arriving in inboxes, especially at Gmail or Outlook
  
• SMTP bouncebacks with rejection codes like:
  

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550 5.7.1 Service unavailable; Client host [IP] blocked

554 5.7.1 Message rejected due to IP reputation

These are red flags that your IP reputation has taken a hit.

How to Check if Your IP Is Blacklisted

Step 1: Identify Your Sending IP Address

If you’re unsure which IP your email is being sent from:

1. Send an email to your personal Gmail or Outlook address
   
2. Open the email and view original / full headers
   
3. Find the line that says something like:
   

vbnet

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Received: from mail.example.com (123.45.67.89)

Your sending IP is 123.45.67.89.

Step 2: Run an IP Blacklist Lookup

Use the following tools to check your IP against major DNS-based blacklists (DNSBLs):

Top Free IP Blacklist Lookup Tools

Tool	What It Does
MxToolbox	Checks your IP against 80+ major blacklists
Talos Intelligence	Provides Cisco’s IP reputation rating
Spamhaus Lookup	Checks listings on Spamhaus SBL/XBL/PBL
MultiRBL.valli.org	Advanced DNSBL lookup with historical data
Abusix Lookup	Checks IP and domain across Abusix’s threat network

Just paste your IP into any of these tools and scan for blacklist appearances.

Understanding the Results

If the lookup shows:

• Not Listed across all blacklists: your IP is clean
  
• Listed on a few obscure lists: monitor and take preventive action
  
• Listed on major blacklists (e.g., Spamhaus, SORBS, Barracuda): you’ll likely experience delivery issues
  

Important: One listing can damage your sender reputation—especially for Gmail, Yahoo, and Outlook.

What to Do If Your IP Is Blacklisted

1. Stop sending from that IP temporarily to avoid more damage
   
2. Audit your logs to find suspicious traffic or spam bursts
   
3. Check for compromised accounts or scripts
   
4. Clean your email lists (remove bounced, inactive, or purchased contacts)
   
5. Fix the root issue before requesting delisting
   
6. Submit delisting requests to the blacklist provider
   
   • Follow instructions from sites like Spamhaus Delist
     

Tip: Many blacklists require you to show you’ve fixed the issue before they’ll delist you.

Prevent Future Blacklistings

• Use SPF, DKIM, and DMARC to authenticate your email
  
• Regularly clean your recipient lists
  
• Monitor your outbound traffic for anomalies
  
• Use rate limiting and outbound spam filters
  
• Avoid shared IPs with poor reputation—or protect shared environments with filtering
  

Let MailChannels Handle It for You

MailChannels SMTP Relay:

• Automatically filters outbound spam
  
• Detects compromised senders in real time
  
• Keeps your IPs off blacklists
  
• Provides diagnostics with ResponseAnalytics
  

 Try MailChannels Free →

Keep Learning

• How to Check Your IP Reputation (Tools & Step-by-Step)
  
• Top Reasons IPs Get Blacklisted (And How to Avoid It)
  
• Complete Guide to IP Reputation Management
  
• What Is IP Reputation? And Why It Matters for Email Delivery