IP and mail server blacklist checker
Find out whether a mail server's IP address is on the spam blocklists that receivers use, with what each listing means and how to get off.
Results for lp.www.cloudflare.com
Not listed
Not on any of the 24 lists that answered
Mailbox providers also use private reputation systems, so this is good news rather than a guarantee.
24 lists asked2 addresses
At a glance
0 listed, 24 clean, 0 did not answer.
- lp.www.cloudflare.com has no MX record, so mail goes to its own address (RFC 5321). That address was checked.
Mail servers2
104.16.123.96Clean on 12
BackscatterNot listed
- List
- Backscatterer.org
- Counts as
- Advisory: few mail servers block on it
- Result
- Not listed.
- Answered in
- 37 ms
BarracudaNot listed
- List
- Barracuda Reputation Block List
- Counts as
- Serious: widely used by mail servers
- Result
- Not listed.
- Answered in
- 196 ms
blocklist.deNot listed
- List
- blocklist.de
- Counts as
- Advisory: few mail servers block on it
- Result
- Not listed.
- Answered in
- 32 ms
DroneBLNot listed
- List
- DroneBL
- Counts as
- Serious: widely used by mail servers
- Result
- Not listed.
- Answered in
- 104 ms
MailspikeNot listed
- List
- Mailspike BL
- Counts as
- Serious: widely used by mail servers
- Result
- Not listed.
- Answered in
- 55 ms
PSBLNot listed
- List
- Passive Spam Block List (PSBL)
- Counts as
- Advisory: few mail servers block on it
- Result
- Not listed.
- Answered in
- 122 ms
SpamCopNot listed
- List
- SpamCop
- Counts as
- Serious: widely used by mail servers
- Result
- Not listed.
- Answered in
- 19 ms
SEM-BLNot listed
- List
- SpamEatingMonkey SEM-BL
- Counts as
- Advisory: few mail servers block on it
- Result
- Not listed.
- Answered in
- 202 ms
Spamhaus ZENNot listed
- List
- Spamhaus ZEN
- Counts as
- Serious: widely used by mail servers
- Result
- Not listed.
- Answered in
- 91 ms
UCEPROTECT 1Not listed
- List
- UCEPROTECT Level 1
- Counts as
- Advisory: few mail servers block on it
- Result
- Not listed.
- Answered in
- 26 ms
UCEPROTECT 2Not listed
- List
- UCEPROTECT Level 2
- Counts as
- Advisory: few mail servers block on it
- Result
- Not listed.
- Answered in
- 37 ms
UCEPROTECT 3Not listed
- List
- UCEPROTECT Level 3
- Counts as
- Advisory: few mail servers block on it
- Result
- Not listed.
- Answered in
- 37 ms
104.16.124.96Clean on 12
BackscatterNot listed
- List
- Backscatterer.org
- Counts as
- Advisory: few mail servers block on it
- Result
- Not listed.
- Answered in
- 41 ms
BarracudaNot listed
- List
- Barracuda Reputation Block List
- Counts as
- Serious: widely used by mail servers
- Result
- Not listed.
- Answered in
- 193 ms
blocklist.deNot listed
- List
- blocklist.de
- Counts as
- Advisory: few mail servers block on it
- Result
- Not listed.
- Answered in
- 29 ms
DroneBLNot listed
- List
- DroneBL
- Counts as
- Serious: widely used by mail servers
- Result
- Not listed.
- Answered in
- 102 ms
MailspikeNot listed
- List
- Mailspike BL
- Counts as
- Serious: widely used by mail servers
- Result
- Not listed.
- Answered in
- 34 ms
PSBLNot listed
- List
- Passive Spam Block List (PSBL)
- Counts as
- Advisory: few mail servers block on it
- Result
- Not listed.
- Answered in
- 120 ms
SpamCopNot listed
- List
- SpamCop
- Counts as
- Serious: widely used by mail servers
- Result
- Not listed.
- Answered in
- 20 ms
SEM-BLNot listed
- List
- SpamEatingMonkey SEM-BL
- Counts as
- Advisory: few mail servers block on it
- Result
- Not listed.
- Answered in
- 112 ms
Spamhaus ZENNot listed
- List
- Spamhaus ZEN
- Counts as
- Serious: widely used by mail servers
- Result
- Not listed.
- Answered in
- 121 ms
UCEPROTECT 1Not listed
- List
- UCEPROTECT Level 1
- Counts as
- Advisory: few mail servers block on it
- Result
- Not listed.
- Answered in
- 26 ms
UCEPROTECT 2Not listed
- List
- UCEPROTECT Level 2
- Counts as
- Advisory: few mail servers block on it
- Result
- Not listed.
- Answered in
- 35 ms
UCEPROTECT 3Not listed
- List
- UCEPROTECT Level 3
- Counts as
- Advisory: few mail servers block on it
- Result
- Not listed.
- Answered in
- 51 ms
Not checked
Our list of blocklists was last checked against live test queries on 2026-11-14. Dead lists (SORBS, CBL and others) are left out, so a list you know may be missing on purpose.
Structured result (JSON) · 15 KB
{
"target": "lp.www.cloudflare.com",
"mode": "ip",
"scope": "mx",
"registryVerified": "2026-11-14",
"notChecked": [],
"verdict": "clean",
"subjects": [
{
"kind": "ip",
"value": "104.16.123.96",
"source": "a",
"listed": 0,
"clean": 12,
"errors": 0,
"refused": 0,
"skipped": 0,
"results": [
{
"id": "backscatterer",
"name": "Backscatterer.org",
"shortName": "Backscatter",
"zone": "ips.backscatterer.org",
"delistUrl": "https://www.backscatterer.org/?target=test",
"delistNote": "Make your mail server reject bad mail while the sender is still connected, instead of bouncing it. The listing then lapses.",
"codes": [],
"weight": 0,
"weightClass": "low",
"policy": false,
"category": "backscatter",
"status": "clean",
"meaning": "Not listed.",
"ms": 37
},
{
"id": "barracuda",
"name": "Barracuda Reputation Block List",
"shortName": "Barracuda",
"zone": "b.barracudacentral.org",
"delistUrl": "https://www.barracudacentral.org/rbl/removal-request",
"delistNote": "Ask for removal with Barracuda's request form, once the cause is fixed.",
"codes": [],
"weight": 0,
"weightClass": "high",
"policy": false,
"category": "reputation",
"status": "clean",
"meaning": "Not listed.",
"ms": 196
},
{
"id": "blocklist-de",
"name": "blocklist.de",
"shortName": "blocklist.de",
"zone": "bl.blocklist.de",
"delistUrl": "https://www.blocklist.de/en/delist.html",
"delistNote": "Listings last about 48 hours after the last report. Fix the attacked or hacked service first, then use its delist page.",
"codes": [],
"weight": 0,
"weightClass": "low",
"policy": false,
"category": "exploit",
"status": "clean",
"meaning": "Not listed.",
"ms": 32
},
{
"id": "dronebl",
"name": "DroneBL",
"shortName": "DroneBL",
"zone": "dnsbl.dronebl.org",
"delistUrl": "https://dronebl.org/lookup",
"delistNote": "Look the address up on DroneBL to see what it saw, then ask for removal once the machine is cleaned.",
"codes": [],
"weight": 0,
"weightClass": "high",
"policy": false,
"category": "exploit",
"status": "clean",
"meaning": "Not listed.",
"ms": 104
},
{
"id": "mailspike",
"name": "Mailspike BL",
"shortName": "Mailspike",
"zone": "bl.mailspike.net",
"delistUrl": "https://mailspike.io/ip_verify",
"delistNote": "Use Mailspike's address check page to see the score and ask for a review.",
"codes": [],
"weight": 0,
"weightClass": "high",
"policy": false,
"category": "reputation",
"status": "clean",
"meaning": "Not listed.",
"ms": 55
},
{
"id": "psbl",
"name": "Passive Spam Block List (PSBL)",
"shortName": "PSBL",
"zone": "psbl.surriel.com",
"delistUrl": "https://psbl.org/remove",
"delistNote": "Use the web form on the PSBL site once the spam source is fixed.",
"codes": [],
"weight": 0,
"weightClass": "low",
"policy": false,
"category": "spam-source",
"status": "clean",
"meaning": "Not listed.",
"ms": 122
},
{
"id": "spamcop",
"name": "SpamCop",
"shortName": "SpamCop",
"zone": "bl.spamcop.net",
"delistUrl": "https://www.spamcop.net/bl.shtml",
"delistNote": "Listings expire 24 hours after the last report. There is no form to fill in.",
"codes": [],
"weight": 0,
"weightClass": "high",
"policy": false,
"category": "spam-source",
"status": "clean",
"meaning": "Not listed.",
"ms": 19
},
{
"id": "sem-bl",
"name": "SpamEatingMonkey SEM-BL",
"shortName": "SEM-BL",
"zone": "bl.spameatingmonkey.net",
"delistUrl": "https://spameatingmonkey.com/services",
"delistNote": "Use SpamEatingMonkey's own page once the spam has stopped.",
"codes": [],
"weight": 0,
"weightClass": "low",
"policy": false,
"category": "spam-source",
"status": "clean",
"meaning": "Not listed.",
"ms": 202
},
{
"id": "spamhaus-zen",
"name": "Spamhaus ZEN",
"shortName": "Spamhaus ZEN",
"zone": "zen.spamhaus.org",
"delistUrl": "https://check.spamhaus.org/",
"delistNote": "Look the address up on Spamhaus's own checker: it shows which list it is on and how to ask. A PBL listing is lifted by the network that owns the range, not by you.",
"codes": [],
"weight": 0,
"weightClass": "high",
"policy": false,
"category": "spam-source",
"status": "clean",
"meaning": "Not listed.",
"ms": 91
},
{
"id": "uceprotect-1",
"name": "UCEPROTECT Level 1",
"shortName": "UCEPROTECT 1",
"zone": "dnsbl-1.uceprotect.net",
"delistUrl": "https://www.uceprotect.net/en/rblcheck.php",
"delistNote": "Expires after 7 days without new trap hits. Paid express removal is offered; you don't need it.",
"codes": [],
"weight": 0,
"weightClass": "low",
"policy": false,
"category": "spam-source",
"status": "clean",
"meaning": "Not listed.",
"ms": 26
},
{
"id": "uceprotect-2",
"name": "UCEPROTECT Level 2",
"shortName": "UCEPROTECT 2",
"zone": "dnsbl-2.uceprotect.net",
"delistUrl": "https://www.uceprotect.net/en/rblcheck.php",
"delistNote": "This lists a whole network, not your address, so it cannot be removed on request. Ask your hosting provider, or wait for it to expire.",
"codes": [],
"weight": 0,
"weightClass": "low",
"policy": false,
"category": "collateral",
"status": "clean",
"meaning": "Not listed.",
"ms": 37
},
{
"id": "uceprotect-3",
"name": "UCEPROTECT Level 3",
"shortName": "UCEPROTECT 3",
"zone": "dnsbl-3.uceprotect.net",
"delistUrl": "https://www.uceprotect.net/en/rblcheck.php",
"delistNote": "This lists a whole hosting network, so only the provider can fix it. Ask your hosting provider.",
"codes": [],
"weight": 0,
"weightClass": "low",
"policy": false,
"category": "collateral",
"status": "clean",
"meaning": "Not listed.",
"ms": 37
}
]
},
{
"kind": "ip",
"value": "104.16.124.96",
"source": "a",
"listed": 0,
"clean": 12,
"errors": 0,
"refused": 0,
"skipped": 0,
"results": [
{
"id": "backscatterer",
"name": "Backscatterer.org",
"shortName": "Backscatter",
"zone": "ips.backscatterer.org",
"delistUrl": "https://www.backscatterer.org/?target=test",
"delistNote": "Make your mail server reject bad mail while the sender is still connected, instead of bouncing it. The listing then lapses.",
"codes": [],
"weight": 0,
"weightClass": "low",
"policy": false,
"category": "backscatter",
"status": "clean",
"meaning": "Not listed.",
"ms": 41
},
{
"id": "barracuda",
"name": "Barracuda Reputation Block List",
"shortName": "Barracuda",
"zone": "b.barracudacentral.org",
"delistUrl": "https://www.barracudacentral.org/rbl/removal-request",
"delistNote": "Ask for removal with Barracuda's request form, once the cause is fixed.",
"codes": [],
"weight": 0,
"weightClass": "high",
"policy": false,
"category": "reputation",
"status": "clean",
"meaning": "Not listed.",
"ms": 193
},
{
"id": "blocklist-de",
"name": "blocklist.de",
"shortName": "blocklist.de",
"zone": "bl.blocklist.de",
"delistUrl": "https://www.blocklist.de/en/delist.html",
"delistNote": "Listings last about 48 hours after the last report. Fix the attacked or hacked service first, then use its delist page.",
"codes": [],
"weight": 0,
"weightClass": "low",
"policy": false,
"category": "exploit",
"status": "clean",
"meaning": "Not listed.",
"ms": 29
},
{
"id": "dronebl",
"name": "DroneBL",
"shortName": "DroneBL",
"zone": "dnsbl.dronebl.org",
"delistUrl": "https://dronebl.org/lookup",
"delistNote": "Look the address up on DroneBL to see what it saw, then ask for removal once the machine is cleaned.",
"codes": [],
"weight": 0,
"weightClass": "high",
"policy": false,
"category": "exploit",
"status": "clean",
"meaning": "Not listed.",
"ms": 102
},
{
"id": "mailspike",
"name": "Mailspike BL",
"shortName": "Mailspike",
"zone": "bl.mailspike.net",
"delistUrl": "https://mailspike.io/ip_verify",
"delistNote": "Use Mailspike's address check page to see the score and ask for a review.",
"codes": [],
"weight": 0,
"weightClass": "high",
"policy": false,
"category": "reputation",
"status": "clean",
"meaning": "Not listed.",
"ms": 34
},
{
"id": "psbl",
"name": "Passive Spam Block List (PSBL)",
"shortName": "PSBL",
"zone": "psbl.surriel.com",
"delistUrl": "https://psbl.org/remove",
"delistNote": "Use the web form on the PSBL site once the spam source is fixed.",
"codes": [],
"weight": 0,
"weightClass": "low",
"policy": false,
"category": "spam-source",
"status": "clean",
"meaning": "Not listed.",
"ms": 120
},
{
"id": "spamcop",
"name": "SpamCop",
"shortName": "SpamCop",
"zone": "bl.spamcop.net",
"delistUrl": "https://www.spamcop.net/bl.shtml",
"delistNote": "Listings expire 24 hours after the last report. There is no form to fill in.",
"codes": [],
"weight": 0,
"weightClass": "high",
"policy": false,
"category": "spam-source",
"status": "clean",
"meaning": "Not listed.",
"ms": 20
},
{
"id": "sem-bl",
"name": "SpamEatingMonkey SEM-BL",
"shortName": "SEM-BL",
"zone": "bl.spameatingmonkey.net",
"delistUrl": "https://spameatingmonkey.com/services",
"delistNote": "Use SpamEatingMonkey's own page once the spam has stopped.",
"codes": [],
"weight": 0,
"weightClass": "low",
"policy": false,
"category": "spam-source",
"status": "clean",
"meaning": "Not listed.",
"ms": 112
},
{
"id": "spamhaus-zen",
"name": "Spamhaus ZEN",
"shortName": "Spamhaus ZEN",
"zone": "zen.spamhaus.org",
"delistUrl": "https://check.spamhaus.org/",
"delistNote": "Look the address up on Spamhaus's own checker: it shows which list it is on and how to ask. A PBL listing is lifted by the network that owns the range, not by you.",
"codes": [],
"weight": 0,
"weightClass": "high",
"policy": false,
"category": "spam-source",
"status": "clean",
"meaning": "Not listed.",
"ms": 121
},
{
"id": "uceprotect-1",
"name": "UCEPROTECT Level 1",
"shortName": "UCEPROTECT 1",
"zone": "dnsbl-1.uceprotect.net",
"delistUrl": "https://www.uceprotect.net/en/rblcheck.php",
"delistNote": "Expires after 7 days without new trap hits. Paid express removal is offered; you don't need it.",
"codes": [],
"weight": 0,
"weightClass": "low",
"policy": false,
"category": "spam-source",
"status": "clean",
"meaning": "Not listed.",
"ms": 26
},
{
"id": "uceprotect-2",
"name": "UCEPROTECT Level 2",
"shortName": "UCEPROTECT 2",
"zone": "dnsbl-2.uceprotect.net",
"delistUrl": "https://www.uceprotect.net/en/rblcheck.php",
"delistNote": "This lists a whole network, not your address, so it cannot be removed on request. Ask your hosting provider, or wait for it to expire.",
"codes": [],
"weight": 0,
"weightClass": "low",
"policy": false,
"category": "collateral",
"status": "clean",
"meaning": "Not listed.",
"ms": 35
},
{
"id": "uceprotect-3",
"name": "UCEPROTECT Level 3",
"shortName": "UCEPROTECT 3",
"zone": "dnsbl-3.uceprotect.net",
"delistUrl": "https://www.uceprotect.net/en/rblcheck.php",
"delistNote": "This lists a whole hosting network, so only the provider can fix it. Ask your hosting provider.",
"codes": [],
"weight": 0,
"weightClass": "low",
"policy": false,
"category": "collateral",
"status": "clean",
"meaning": "Not listed.",
"ms": 51
}
]
}
],
"summary": {
"subjects": 2,
"asked": 24,
"listed": 0,
"clean": 24,
"errors": 0,
"refused": 0,
"skipped": 0,
"weightedScore": 0
},
"notes": [
"lp.www.cloudflare.com has no MX record, so mail goes to its own address (RFC 5321). That address was checked.",
"A clean result here does not guarantee delivery: Gmail, Outlook and Yahoo judge senders with their own reputation systems, which no public list shows."
],
"dnsQueries": 26
}Next step
- IP lookupWhose network is the address on?Check lp.www.cloudflare.com in IP lookup
- Reverse DNSDoes the address have a matching name?Check lp.www.cloudflare.com in Reverse DNS
- Ping from many placesDoes the address answer?Check lp.www.cloudflare.com in Ping from many places
What a blocklist check tells you
A DNS blocklist (DNSBL, sometimes called an RBL) is a public list of IP addresses that sent spam, were hacked, or should not send mail directly. A receiving mail server looks up the sender's address on the list in DNS, and may reject or junk the message when it finds a match.
Enter an IP address, or a domain to check its mail servers. For a domain we read its MX records and check up to three of the addresses behind them. For each address we ask a dozen live lists and show listed, not listed, or no answer for each.
Which lists we ask, and which we leave out
Many blocklist sites still query lists that closed years ago. SORBS shut down in June 2024, and the CBL was folded into Spamhaus. Asking a dead list gives nothing, or worse, an answer for everything. Each list was tried against known listed and clean addresses before we added it, and we keep only the ones that behaved. The date of that check is shown with every result.
| List | What it lists | How much it matters |
|---|---|---|
| Spamhaus ZEN | Spam sources, hijacked ranges, infected machines and dynamic ranges | High for SBL and XBL, low for the policy list PBL |
| SpamCop | Addresses reported by users or caught in traps in the last day or so | Medium, and clears itself |
| Barracuda | Addresses Barracuda filters rate as poor reputation | Medium, important if you mail Barracuda customers |
| UCEPROTECT 1, 2, 3 | One address, its network block, or its whole provider | Level 1 matters, levels 2 and 3 are collateral |
| PSBL, SEM, blocklist.de | Trap hits and reported attacks | Medium |
| Mailspike, DroneBL, Backscatterer | Reputation scores, infected machines, bounce abuse | Medium to low |
Each list has a weight, and the summary adds up the weights of the lists you are on. A listing on the Policy Block List only says that the range is meant for end users, such as a home connection, and is not a reputation problem.
If you are listed
- Find the cause firstA hacked website form, a compromised mailbox, a computer with malware, an open relay or a bulk campaign to an old list are the usual reasons. Removal requests made before the cause is fixed lead to a new listing within days.
- Check your mail setupMake sure the server has reverse DNS that matches its name, and that SPF, DKIM and DMARC pass. Several lists weigh this when they decide whether to remove you.
- Ask each list to delist youEach list that has you gets a removal link under How to get removed, and on its cell. Many remove an address on their own after a few days of clean behaviour, and some charge for faster service, which you do not need.
- Check again laterCome back after the list says it has removed you. Lists refresh at different speeds, and a cached answer at a receiver can last a few hours.
Domain names have blocklists as well, for the links in your mail. Use the domain blocklist check for those.
What a clean result does not cover
Gmail, Outlook and Yahoo judge senders with private reputation systems built on their own traffic. None of that appears on a public list, so a clean result here does not guarantee delivery. It tells you that the public lists that spam filters commonly use have nothing against you.
Public lists run on donated servers and ask users to keep volume low. We pace our own questions to each list and keep recent answers for a short time, so repeated checks of the same address may show the previous answer. Use the fresh option when you have just been removed.
Questions people ask
What is a DNSBL?
A DNS-based blocklist is a list of IP addresses or domains kept in DNS, so a mail server can check a sender with one fast lookup. Listings have return codes that say why, and each list has its own rules about who is added and how they are removed.
Why does the checker say a list refused us?
Some lists limit free use. Spamhaus, for one, answers with a special error code when it thinks a query is too heavy or comes from a shared resolver. We show that as a refusal, because it tells you nothing about your address. Use the list's own website for a definite answer.
Am I blocked everywhere if I am on one list?
No. Each receiver chooses which lists it uses and how much weight to give them. Being on Spamhaus SBL or XBL is serious because many large receivers use it. A listing on a small list or a policy list affects far fewer messages.
What is the difference between UCEPROTECT levels 1, 2 and 3?
Level 1 lists single addresses that sent spam to its traps. Level 2 lists whole network blocks with several bad senders, and level 3 lists all of a provider's network. Levels 2 and 3 describe your neighbours, so only the provider can clear them.
How long does it take to be removed?
It depends on the list. SpamCop and several trap-based lists expire a listing in a day or two after the spam stops. Others need a request. After removal, receivers may keep the old answer in their cache for a few hours.
Why is a shared hosting or cloud IP listed?
Other customers on the same address or network may have sent spam. Ask your provider to move you to a clean address or to clean up its range, since one customer cannot get a network-wide listing lifted.
Does this check IPv6 addresses?
Yes, but fewer lists cover IPv6. For an IPv6 address we ask only the lists that support it and mark the rest as not asked, so a short list does not look like a full clean bill.
Use it from AI, the API or the command line
Every LookupOwl tool is also a free API and an MCP tool, with no key and no account. This one is blacklist_check. Please be kind to the rate limits.
curl "https://lookupowl.com/api/v1/tools/blacklist-checker?q=8.8.8.8"claude mcp add --transport http lookupowl https://lookupowl.com/mcp