Why Purchased IPs May Be Blacklisted
When you buy IPv4 addresses on the secondary market, you are acquiring addresses that were previously used by another organization. Their past activities may have left blacklist entries that are still active. Deploying blacklisted IPs without checking can cause immediate operational issues.
When to Check
Before Purchase (Due Diligence)
Always check the blacklist status of IPv4 addresses before finalizing your purchase. This should be a standard part of your due diligence process. Use our free IP Blacklist Checker to scan every IP in the block against 300+ blacklists.
After Transfer (Deployment Readiness)
Even if the block was clean at purchase time, check again after the transfer completes and before you start using the addresses. Some blacklists update continuously, and new entries may appear during the transfer period.
How to Check Your IPv4 Block
Step 1: Scan Against Major Blacklists
Go to our IP Blacklist Check tool and enter your subnet (e.g., 185.100.200.0/24). The tool will scan every IP in the range against 300+ blacklists including:
- Spamhaus (SBL, XBL, PBL, CSS)
- Barracuda BRBL
- SORBS
- UCEProtect (Levels 1, 2, 3)
- SpamCop
- CBL (Composite Blocking List)
- And 290+ more
Step 2: Review the Results
For each IP that appears on a blacklist, note:
- Which blacklist it appears on
- The severity (some lists have more impact than others)
- When it was listed (recent vs. old entries)
- The reason for listing
Step 3: Request Delisting
For any active listings, follow the removal procedures. Most blacklists have a self-service removal process. Since the addresses are now under new ownership, removal is typically straightforward.
Step 4: Set Up Monitoring
After cleanup, set up continuous monitoring with our Blacklist Monitoring service. This way, you will be alerted immediately if any of your IPs get listed again in the future.
What If Many IPs Are Blacklisted?
If a significant portion of your purchased block is blacklisted:
- Check your purchase agreement: A good transfer contract includes blacklist warranties from the seller
- Contact the seller/broker: Report the issue and request remediation support
- Systematic cleanup: Address the most impactful blacklists first (Spamhaus, Barracuda)
- Allow time: Some blacklists automatically delist IPs after a period of inactivity
Prevention: Buy Clean IPs
At IPv4.center, we check all listed addresses against major blacklists before they appear on our marketplace. We also include blacklist warranties in our transfer agreements, generated through our contract generator.