IP blacklist check
Probes an IPv4 against 16 public DNS blocklists in one pass.
How this tool works
When emails from your mail server land in spam or get rejected, the sending IP is very likely on a DNS blocklist (DNSBL). This check probes an IPv4 against 16 public reputable DNSBLs — including Spamhaus ZEN (the most-used), Barracuda Reputation Block List, SpamCop, CBL/Abuseat, UCEPROTECT in three tiers, plus specialised lists like Mailspike, SpamRats and PSBL. On top come the URI lists SURBL and URIBL: they list IPs that appear as link targets in spam, not the sending server. Per listing the return codes are shown — they tell you the cause (spam, open relay, snowshoe, botnet). A list that does not answer is reported as not determined, never counted as clean.
Typical use cases
- Mail server diagnosis on "mail goes to spam" reports
- Before IP change or cloud migration, check the new IP reputation
- After incident (compromised account, spam wave), track listings until they clear
- When choosing an outbound provider — which provider IP is potentially already tainted?
Frequently asked questions
Which DNSBLs are most important?
Spamhaus ZEN first — it combines SBL, CSS, XBL and PBL in one lookup. Barracuda BRBL, CBL/Abuseat and SpamCop follow. UCEPROTECT L1 is relevant, L2 and L3 are aggressive and selectively used.
How do I get off a blacklist?
Spamhaus, Barracuda and SpamCop offer removal forms. Prerequisite: the issue (open relay, compromised account, spam script) is fixed. Auto-delisting after 24-48h is common but not guaranteed.
Are URIBL/SURBL relevant for mail servers?
Differently from the other lists: URIBL and SURBL list domains and IP addresses that appear as link targets in spam — not the sending mail server. A hit there means emails linking to that IP or domain get flagged. The other 14 lists rate the sending mail server itself.
Are IPv6 addresses supported?
Not currently — the check only accepts IPv4, although Spamhaus has answered IPv6 lookups since 2016 (SBL and CSS).
Why is my IP on a list even though I did not send anything?
Three common reasons: (1) The IP was newly assigned to you by the provider, was likely compromised before. (2) UCEPROTECT L2/L3 lists entire provider ranges. (3) On shared hosting, other customers on the same server affect your IP reputation.
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