IP Blacklist Checker
Check your sending IP address against more than 100 real-time email blacklists (DNSBLs)
IP Blacklists
Your emails can be written well and still never arrive. If the IP address your mail server sends from has been blacklisted, the receiving server can reject or quietly drop your messages before a spam filter ever reads the content.
This page explains what an IP blacklist is, how the lookups work, why an address ends up on one, and how to get it removed. Enter an IP above to check it against more than 100 blacklists at once.
What Is an IP Blacklist?
An IP blacklist, usually called a DNSBL (DNS-based blocklist) or RBL (real-time blocklist), is a published list of IP addresses linked to spam or abuse. Mail servers query these lists during the SMTP handshake: when your server connects to deliver a message, the receiving server looks up your IP and decides whether to accept, reject, or flag the email.
Each list is run by a separate operator with its own listing rules, so an IP can sit on one list and be absent from a dozen others.
Some of the most widely queried IP blacklists include:
- Spamhaus ZEN: A single lookup that combines the SBL, XBL, and PBL zones. Most large mailbox providers check it, which makes a ZEN listing one of the more consequential ones to fix.
- Spamhaus PBL (Policy Block List): Ranges of addresses that the operator or the ISP says should not be delivering mail directly to the internet, such as residential and dynamically assigned IPs. A PBL listing does not mean the address sent spam.
- Spamhaus XBL: Addresses of compromised machines running open proxies, worms, or bots. It includes the data that was previously published as the Composite Blocking List (CBL).
- SpamCop Blocking List (SCBL): Built from SpamCop user reports and spam-trap hits. Listings expire on their own once the reported spam stops.
- Barracuda Reputation Block List (BRBL): A free list of IPs known to send spam. You register the address you run queries from, then you can use it at no cost.
- UCEPROTECT: A tiered list that, at its higher levels, can list entire network ranges. That breadth catches innocent neighbors along with the actual spammers, so context matters when you read a UCEPROTECT result.
Google, Microsoft, and other large providers also run private reputation systems you cannot query directly. A clean public record helps, but it does not guarantee inbox placement at those providers.
How Do IP Blacklists Work?
A DNSBL is queried over ordinary DNS. To check an IPv4 address, the receiving server reverses the four octets, appends the blocklist's zone, and asks for an A record.
For example, to check 192.0.2.45 against Spamhaus ZEN, the server looks up 45.2.0.192.zen.spamhaus.org:
- If the lookup returns an address in the 127.0.0.0/8 range, the IP is listed, and the exact return code says why. With Spamhaus, 127.0.0.2 means the SBL, 127.0.0.4 to 127.0.0.7 indicate the XBL or CSS, and 127.0.0.10 or 127.0.0.11 mean the PBL.
- If the lookup returns NXDOMAIN, meaning no record exists, the IP is not on that list.
Because the whole exchange is a single DNS query, a receiving server can check several blocklists in the few hundred milliseconds before it decides whether to accept your connection. That speed is why these lists run at the front of mail acceptance, ahead of content filtering.
Why Does an IP Get Blacklisted?
An IP earns a listing through behavior the operator treats as abusive, or through where it sits on the network.
- Hitting spam traps. These are addresses that never signed up for anything. A trap hit is strong evidence that a list contains scraped or purchased addresses.
- A sudden jump in volume. A new or quiet IP that starts sending tens of thousands of messages looks like a hijacked machine, and filters react accordingly.
- Spam complaints. When recipients press the report-spam button often enough, feedback loops pass that signal back to the blocklists and the mailbox providers.
- Compromised infrastructure. A server running an open relay, an open proxy, or malware gets listed on the XBL once it starts emitting spam.
- The neighborhood. On shared hosting or a shared sending IP, another customer's behavior can list the address you also send from. The PBL can list an entire residential or dynamic range regardless of what any single host does.
- Missing or generic reverse DNS. An IP with no PTR record, or a default PTR like 192-0-2-45.dynamic.example.net, reads as a low-trust sender to many receivers.
How to Check If Your IP Is Blacklisted
Find the public IP your mail actually leaves from. For a hosted mail service that is their outbound IP, not your office connection. Then run it through a checker that queries many lists at once, like the tool at the top of this page. Check the IP itself, not only your domain, since the two can hold completely different reputations.
If you send through Google Workspace, Microsoft 365, or a provider like Mailchimp or SendGrid, you usually share their IPs and cannot delist them yourself. A listing there is the provider's to manage, though your own sending habits still affect the shared reputation.
How to Remove Your IP from a Blacklist
Removal starts with fixing whatever caused the listing. Delisting a server that is still sending spam just gets it relisted within hours.
For Spamhaus, use the Blocklist Removal Center. SBL listings are reviewed by Spamhaus staff. XBL and CSS listings usually allow a one-time self-service removal, but the IP returns if the underlying infection or misconfiguration is still active. A PBL listing on a static IP you control can be removed through the same center; otherwise the ISP has to authorize it.
Report-driven lists such as SpamCop expire on their own, often within a day, once the spam stops, so there is frequently nothing to submit. For smaller lists with no automated form, email the operator, explain what changed, and ask for removal. Keep the message short and factual.
Email warmup tools like Warmup Inbox can help you rebuild the reputation of a sending IP after a listing.How to Keep Your Sending IP Off Blacklists
Staying off blacklists is ongoing work. The steps below cover the parts that matter most for a sending IP.
Set Up rDNS and Authentication
Give your sending IP a PTR record that matches the hostname your server announces in its SMTP greeting, and make sure forward and reverse DNS agree (forward-confirmed reverse DNS). Publish SPF, DKIM, and DMARC for your domain. Receivers use these together to judge whether an unfamiliar IP is worth trusting.
Warm Up New IPs
A brand-new IP has no reputation, and pushing full volume onto it reads as an attack. Start with a few hundred messages a day to your most engaged recipients, then roughly double the volume every few days while you watch bounce and complaint rates.
Clean Your List Before You Send
Spam traps and dead addresses are the quickest route onto the XBL and the report-driven lists. Verifying your list with a tool like EmailListVerify removes the invalid addresses and known traps that trigger those listings in the first place.
Watch Complaint and Bounce Rates
A complaint rate above roughly 0.1%, or one in a thousand, is enough to draw attention at the major mailbox providers. Honor unsubscribes right away, keep the unsubscribe link easy to find, and stop mailing addresses that bounce.
Keep Volume Steady
Receivers learn what normal looks like for your IP. Large, irregular spikes, such as a five-fold jump for a single campaign, can trip volume-based filters even when the mail is wanted. Spread big sends out where you can.
Frequently Asked Questions
How is an IP blacklist different from a domain blacklist?
An IP blacklist (a DNSBL) lists the address of the server connecting to deliver mail. A domain or URI blacklist, such as URIBL or SURBL, lists domains that appear inside the message body. A message can be stopped by either: a bad sending IP ends the connection, while a blacklisted link in the content gets the mail filtered after it is read.
How long does an IP stay blacklisted?
It depends on the list. Report-driven lists like SpamCop drop an IP automatically once the spam stops, sometimes within hours. Lists like Spamhaus keep an entry until you fix the cause and request removal, or until the listed condition clears on its own.
Can one blacklisting block my email?
It can, if the list is one the large providers consult. A Spamhaus ZEN listing carries far more weight than an entry on an obscure list almost no one queries. Check which lists flagged the IP before you worry about all of them.
I'm on a shared IP I don't control. What can I do?
Raise it with your host or email service provider, since only they can request delisting for an address you share. In the meantime, keep your own sending clean so you are not adding to the shared reputation problem.
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