This free IP blacklist check shows whether an address is on public spam blocklists.
Enter an IPv4 address to see whether public spam blocklists list it. It is free, with no signup.
Free & rate-limited. No signup required to try.
Example resultThis is a real lookup we captured on 2026-10-23 for 8.8.8.8. Run any lookup above and it is replaced with yours.
Not listed on any of the 3 public spam blocklists
An IP blacklist check shows whether an IP address is listed on public spam blocklists, the databases mail servers use to refuse mail from addresses that sent spam. 1Lookup's free checker asks several public spam blocklists about any IPv4 address and shows how many list it, and whether any list could not be asked.
- No signup to try
- Asks the lists directly
- Not checked is never shown as clear
You can check an IP address in four steps.
Enter the address.
Paste the IPv4 address your mail server sends from, or the one named in a bounce message.
Read the headline.
It says how many lists include the address, or that none of the lists that answered do.
Look for Not checked.
A list that did not answer is counted as unknown, so a clean headline means every list was asked.
Contact the list that has you.
The bounce message names the list that rejected your mail. Each list runs its own removal process, and only that list can remove you.
Source: RFC 5782: DNS Blacklists and Whitelists, published by IETF.
Need this at scale? IP Lookup API
A fraud score, risk level and VPN, proxy and Tor flags for every connection you see.
An IP blacklist check asks public spam blocklists whether an address is on them.
If your email is bouncing or your server traffic is being refused, a blacklisted IP is a common cause. A blacklist, also called a blocklist or DNSBL, is a public database of IP addresses that were seen sending spam or abuse. Mail servers ask these lists about the address that is connecting, and may refuse, delay or tag the message when they find it.
This free check makes the same lookup a mail server makes. It reverses the four numbers of your address, asks each list about it over DNS and reports what came back, the way RFC 5782 describes. The answer comes from the lists, not from a score we calculate from other signals.
Use this page when you have one address in front of you: your mail server's outbound IP, a new cloud address or an IP from a log. When the check has to run for every signup or send, the IP lookup API adds the fraud score and the risk factors behind it.
Building this into a risk score?
A blocklist hit is one signal among several. For the location, network and anonymizer fields that sit beside it on a single lookup, and how to combine them, read our IP geolocation API guide. To fold the address into one risk level and a 0 to 100 score, use our free IP fraud score checker. To test one proxy IP address, with its port if you have one, and see how it is flagged, use our free proxy checker.
The check takes three steps and sends nothing to the owner of the address.
You enter an IP address.
Paste a public IPv4 address. Private ranges such as 192.168.0.1 are on no public list, and IPv6 addresses show as Not checked.
We ask the blocklists.
The four numbers of the address are reversed and sent to each list as a DNS question, the same lookup a receiving mail server makes. A list answers with a code if the address is on it and with no record if it is not.
You see who answered.
The result shows how many lists include the address and how many answered. A list that timed out or refused the question is shown as Not checked, never as clear.
A blocklist lookup is a DNS question with the four numbers reversed.
RFC 5782 describes how an IPv4 address is looked up under a blocklist's zone name. The steps below use the address 203.0.113.42 and the reserved zone name example-list.test.
| Step | What happens | Example |
|---|---|---|
| 1 | The four numbers of the address are written in reverse order | 42.113.0.203 |
| 2 | The list's zone name is added to the end | 42.113.0.203.example-list.test |
| 3 | An A record is requested for that name | A query for 42.113.0.203.example-list.test |
| 4 | An answer in 127.0.0.0/8 means the address is listed, most often 127.0.0.2 | 127.0.0.2 |
| 5 | No such name means the address is not listed | NXDOMAIN |
The result on this page is one of four states.
Each state follows from what the lists returned for the address.
| Result | What it means | What to do |
|---|---|---|
| Not listed on any list | Every list that was asked has no record for the address | Nothing to remove. If mail still fails, look at your sending setup and mail volume |
| Listed on one or more lists | At least one list has a record for the address | Open the list named in your bounce message, fix the cause, then ask that list to remove you |
| Not listed, with some lists Not checked | The lists that answered have no record, and the others could not be asked | Run the check again in a few minutes |
| Not checked | No list answered, or the address is IPv6 or not a public address | Try again later, or enter a public IPv4 address |
The answer comes from the lists themselves.
Each result is what the lists returned for your address, not a score made up from other signals.
A list that stays silent never counts as clear.
Timeouts, refusals and lists that fail their own test lookup show as Not checked, so a clean headline means every list was really asked.
The test address shows what a listing looks like.
Every IPv4 blocklist carries 127.0.0.2 for testing, so entering it shows a listing without needing a blacklisted server.
No account is needed to check.
Run the check right away and see the answer in a few seconds.
Who uses this tool
Find out why your email is bouncing.
A sender whose messages are rejected or land in spam can check whether the sending IP is on public spam blocklists before contacting a mailbox provider.
Vet a new or recycled server address.
Sysadmins can check a newly assigned cloud or hosting IP to see whether a previous user left it listed.
Check an address from a log or an alert.
Security teams can paste an address from a firewall log, a mail log or an alert and see whether the lists know it.
Check an address before you trust it.
Support and trust teams can check the address behind a signup or a login before treating the connection as clean.
Frequently asked questions
How do I know if my IP is blacklisted?
Enter it above. If your mail is being refused, the bounce message usually names the list that rejected it, with an SMTP code such as 550 or 554. A listing here together with those symptoms means the address needs removal from that list.
Why is my IP blacklisted?
IPs usually get blacklisted because spam or abuse traffic came from them, a mail server or script was compromised, a relay or proxy was left open, malware was active on the network, or a previous owner of the address left a bad history. Sudden spikes in sending volume can also trigger a listing.
How do I check if my IP is blacklisted?
Paste your public IPv4 address into the box above and run the check. The page asks each list directly and shows how many of them include the address.
Does this check every blocklist?
No. It asks a set of public spam blocklists that allow free lookups. Other lists exist and each keeps its own records, so a bounce message that names a different list needs a lookup on that list.
Why does a list show as Not checked?
The list did not answer in time, refused the question or failed its own test lookup. Some lists refuse requests that come from shared hosting networks. Run the check again in a few minutes.
How do I remove my IP from a blacklist?
First fix the root cause: stop the spam or abuse, secure compromised systems and close open relays. Then ask each list that includes the address to remove it, because every list runs its own removal process and some drop an address on their own once the reports stop.
How fresh is the result?
Each list is asked directly, and the answer is kept for ten minutes so repeat checks of the same address do not keep hitting the lists. A removal shows up here once the list has dropped the address and the ten minutes have passed.
Can I check an IPv6 address?
You can enter one, but the blocklist fields show Not checked, because not every list covers IPv6. Use an IPv4 address for a real answer.
Can I test the checker with a known listing?
Yes. Enter 127.0.0.2, the test address RFC 5782 requires every IPv4 blocklist to carry. The lists that answer it as a listing show as Listed, so you can see what a listing looks like.
How does a blacklisted IP affect email deliverability?
When your sending IP is on a spam blocklist, receiving mail servers may reject your messages, defer them or route them to the spam folder. That hurts deliverability and engagement, so checking and clearing listings is a key step in protecting your email program.
What is the difference between a blacklist check and a fraud score?
A blacklist check answers one question: is this address on a spam database. A fraud score rates how risky a connection looks from signals such as VPN, proxy, Tor and datacenter use. The free IP fraud score checker covers the second.
Can I check IPs in bulk or through an API?
This page checks one address at a time. For many addresses, the 1Lookup IP lookup API returns the fraud score, risk level and VPN, proxy and Tor flags in one call per address, and a 7-day free trial lets you test it on your own traffic.
These pages check the same address in other ways.
- IP fraud score checkerA risk level and the VPN, proxy, Tor and datacenter flags for the same address.
- VPN and proxy detectionWhether the address is a VPN, proxy, Tor exit node or datacenter host.
- SPF record checkerWhether your domain's SPF record lets your mail server send for it.
- DMARC checkerThe policy that tells receivers what to do with mail that fails authentication.