IP Blacklist Check (DNSBL) + Spam Score
Check whether an IP address sits on a DNS blacklist (DNSBL) — the reputation lists that mail servers consult before accepting a message — and get its public spam score. Enter an IPv4 address or a domain (SysGlass resolves the domain to its IPv4), and the tool queries 13 reputable blacklists in parallel plus StopForumSpam (a free 0-100 spam confidence). A single listing can quietly send your outbound mail to the spam folder or get it rejected at the door, so this is a first stop when email stops being delivered.
Reviewed by the SysGlass team · Updated July 21, 2026
What it checks
- Tests one IPv4 address — or a domain resolved to its first IPv4 (A record) — against 13 DNS blacklists.
- Lists checked include Spamhaus ZEN, SpamCop, Barracuda, SORBS, PSBL, Mailspike, UCEPROTECT L1, NiX Spam, DroneBL, SpamRATS and more.
- A StopForumSpam spam score: a free, keyless 0-100 confidence plus how often and how recently the IP was reported (and whether it's a Tor exit). Best-effort — if the source is down we say 'unavailable' rather than guess.
- Returns a listed/clean status for every list, plus a count of how many list the IP.
- Distinguishes a genuine listing (a 127.0.0.0/8 DNS answer) from a DNSBL error or info code (the reserved 127.255.255.0/24 range), which is not counted as a listing.
- Shows the equivalent dig command for the check (e.g. dig +short <reversed-ip>.zen.spamhaus.org) so you can reproduce it yourself.
- When the IP is listed, returns delisting guidance pointing to each list's own removal page (such as spamhaus.org/lookup).
How to read the result
- Clean (pass): a message like "<IP> is not listed on any of the 13 blacklists checked and clean on StopForumSpam" means no list is blocking that address.
- Listed (fail): the summary names which lists flagged the IP and the count, e.g. "listed on 2 of 13: Spamhaus ZEN, SORBS", and includes a high StopForumSpam spam confidence when present.
- Each result row shows a list name with either clean or LISTED — read the per-list rows to see exactly where the problem is.
- A LISTED status means receivers that use that list may defer, reject, or spam-folder mail sent from this IP.
- Spamhaus ZEN is the most consequential listing — it is consulted by many large mailbox providers, so a hit there has the biggest deliverability impact.
- Error verdict: the input could not be resolved to an IPv4 address, or the results could not be read — check that the host has an A record and is reachable.
Frequently asked questions
Can I check a domain instead of an IP?
Yes. If you enter a domain, SysGlass resolves it to its first IPv4 (A record) and checks that address. DNSBLs list IP addresses rather than domain names, so for mail sending the IP your server uses is what actually gets evaluated by receivers.
Which blacklists does this tool check?
Thirteen widely used, reputable DNSBLs: Spamhaus ZEN, SpamCop, Barracuda, SORBS, PSBL, Mailspike, UCEPROTECT L1, NiX Spam, WPBL, GBUdb Truncate, DroneBL, SpamRATS and s5h. Spamhaus ZEN is the single most important because so many providers consult it; the others add coverage for different listing reasons.
What is the spam score, and is it the same as CleanTalk's?
It's a free, public per-IP spam reputation from StopForumSpam: a 0-100 confidence plus how many times and how recently the IP was reported. It's an equivalent free signal to a vendor score like CleanTalk's — not the same proprietary number, but built from open data you can verify. A high confidence is a real reputation hit even before a DNSBL catches up.
My IP is listed — how do I get delisted?
First find and fix the underlying cause: an open relay, a compromised host or mailbox sending spam, or reputation inherited from a shared IP. Once the cause is resolved, request removal at each list's own site (for example, spamhaus.org/lookup). Delisting is not instant, and recent listings can take time to clear even after the problem is fixed.
Does this check IPv6 addresses?
No — the check is IPv4 only. If you pass an IPv6 address, or a domain that only has AAAA records, the tool cannot run the lookup and will report that it could not resolve an IPv4 address.
Will a listing actually block my email?
It depends on the receiving server. Many mail servers reject or spam-folder messages based on these lists, so even one listing on a major DNSBL like Spamhaus ZEN can noticeably hurt deliverability. A clean result here doesn't guarantee inbox placement, but a listing is a concrete, fixable cause of delivery problems.
How does it tell a real listing from a DNSBL error?
DNSBLs answer queries with addresses in 127.0.0.0/8. The 127.255.255.0/24 block is reserved for error and info codes — for example, a warning that queries via a public resolver are rate-limited. SysGlass treats those reserved codes as not listed, so they don't produce a false positive.
Is the result live or cached?
It is a live lookup. Each run queries the 13 blacklist zones and StopForumSpam in real time (with a short overall timeout), so the result reflects the reputation at the moment you run it.