What an IP blacklist check tells you
An IP blacklist (also called a DNSBL or RBL) is a public list of IP addresses that have sent spam, hosted malware, or show signs of a compromised or misconfigured server. Mailbox providers and corporate spam filters query these lists in real time when your server connects to them. If your sending IP is on a list they trust, your mail can be rejected outright, delayed, or sent straight to the spam folder.
Our checker asks each list one simple DNS question about your IP and reports the answer. A listed result shows the list name, the return code the list gave, and a link to that list's removal steps in our blacklist directory. A clean result means none of the lists we query has your IP right now. If you want the background first, our guide on what an IP blacklist is covers how listings happen.
How to check an IP manually
You can run the same lookup yourself from a terminal. DNS blacklists work by reversing the four parts of the IP and adding the list's zone name. For the IP 203.0.113.10 and Spamhaus ZEN, you would query 10.113.0.203.zen.spamhaus.org.
- 1 Reverse the octets of the IP, so 203.0.113.10 becomes 10.113.0.203.
- 2 Append the list zone, for example zen.spamhaus.org or b.barracudacentral.org.
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3
Run
dig +short 10.113.0.203.zen.spamhaus.org Aor the same name with nslookup. - 4 No answer (NXDOMAIN) means not listed. An answer in the 127.0.0.x range means listed, and the last number tells you why.
- 5 Repeat for every list you care about. That is the slow part, which is why a checker runs them all at once.
Which blacklists matter most
Not every list carries the same weight. A few are used by a large share of the world's mail servers, while others are small and rarely consulted. Here is how the main ones compare.
| Blacklist | What it lists | Impact |
|---|---|---|
| Spamhaus ZEN | Spam sources, hijacked hosts, dynamic IP ranges (SBL, XBL, PBL combined) | Very high, widely used by providers and filters |
| Barracuda BRBL | IPs seen sending spam to Barracuda customers | High in business mail filtering |
| SpamCop | IPs reported by users, listings expire on their own | Medium, short lived |
| UCEPROTECT L1 | Single IPs that hit spam traps | Low to medium, L2 and L3 list whole networks |
| PSBL, Mailspike, SpamRATS | Spam trap hits and suspicious behavior | Varies by receiver |
What to do if your IP is listed
Do not request removal first. Lists that see the same problem continue after delisting will relist you, and some make the second removal harder. Find the cause, fix it, then ask for removal.
- 1 Read the return code and the list's lookup page. It usually says whether the listing came from spam trap hits, user complaints, or a known infected host.
- 2 Check the server for compromised accounts, open relays, or a script sending mail you did not plan. On shared hosting, ask your provider.
- 3 Look at your list sources. Purchased lists and old addresses are the most common cause of spam trap hits.
- 4 Make sure the IP has a PTR record (reverse DNS) that matches a hostname which resolves back to the same IP.
- 5 Submit the removal request on the list's own site. Some lists, like SpamCop, expire on their own within a day or two once the problem stops.
IP vs domain blacklists
This page checks the IP your mail leaves from. Spam filters also check the domains inside your message, such as the domain in your links and your From address, against domain lists like Spamhaus DBL, SURBL and URIBL. An IP can be clean while your domain is listed, and the reverse. Run a domain blacklist check as well, and look at the wider picture with the IP reputation checker, which adds reverse DNS and provider signals to the list results.
If you send through a shared platform like a newsletter or CRM tool, the sending IP belongs to that provider. A listing there is usually theirs to fix, but it still affects your mail, so it is worth knowing about.
Why a one-off check is not enough
Listings happen without warning. A compromised mailbox can send thousands of messages overnight, and a listing on a major list can block mail to many receivers before anyone notices. Most teams find out from a bounce or a customer complaint, often days later.
BlacklistMonitoring checks every domain and IP you send from on 100+ lists as often as every 5 minutes, depending on your plan, and alerts you by email, Slack, Microsoft Teams or webhook the moment a listing appears. Each alert includes the list, the reason code and the removal steps. You also get listing history, so you can see when a problem started and how long it lasted. See IP blacklist monitoring for how it works, or compare plans on the pricing page.
- Starter covers 10 domains and IPs with checks every 60 minutes.
- Business covers 100 domains and IPs with checks every 15 minutes.
- Scale adds CIDR range monitoring, so you can watch a whole block of sending IPs.
- All checks are DNS lookups only. Nothing is ever sent from or to your mail server.
Frequently asked questions
How do I check if my IP is blacklisted?
Enter the IP in the checker above and it queries 100+ DNS blacklists at once. You can also check a single list by reversing the IP octets, adding the list zone, and running a DNS lookup. An answer in 127.0.0.x means listed.
How long does it take to get off a blacklist?
It depends on the list. SpamCop listings expire on their own within about 24 hours after the spam stops. Spamhaus and Barracuda usually act on a removal request within hours to a day, once the cause is fixed. UCEPROTECT L1 expires after 7 days without new hits.
Why is my IP blacklisted when I never sent spam?
Common reasons are a compromised account or website script sending mail, an IP you inherited from a previous user, a dynamic or residential IP range listed by Spamhaus PBL, or a network-wide listing like UCEPROTECT L2 or L3 caused by other customers of your host.
Is this IP blacklist checker free?
Yes. The one-off check is free and needs no account. Creating an account unlocks the full report once. Continuous monitoring and alerts are part of the paid plans, starting with Starter.
Does a blacklist listing mean my emails are blocked everywhere?
No. Each receiver chooses which lists to use. A Spamhaus ZEN listing affects a large share of receivers, while a listing on a small list may affect very few. That is why the impact column matters more than the total count.