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Relaymetry

Blacklist lookup

Check whether your mail-server IPs are listed on email blacklists. Instant, no signup, plain English.

Quick answer: DNS-based blocklists are public lookup services that flag IPs and domains observed sending unwanted mail. This tool resolves your MX records, then queries each MX-target IP against several DNSBL zones (Barracuda, SpamCop, UCEPROTECT, Mailspike, PSBL, Spamhaus ZEN). A clean blocklist result is one signal of healthy outbound mail; a listing usually means investigation and delisting are needed before mail flows reliably.

What this checks

DNSBL (DNS-based blocklist) zones are public lookup services that list IP addresses or domains observed sending unwanted mail. Per RFC 5782, the lookup format is a reversed-octet IP query against the zone's apex (e.g., 4.3.2.1.zen.spamhaus.org); a returned A record (127.0.0.x) signals a listing, with the last octet encoding the listing reason. Relaymetry first resolves the requested domain's MX records, then queries each MX target's IPv4 address against a curated set of public zones: Barracuda, SpamCop, UCEPROTECT L1/L2, Mailspike, PSBL, and Spamhaus ZEN. We do not query commercial subscription zones, do not list IPv6-only mail hosts (per accepted-limitation L2), and do not query zones with restricted query policies.

How to read the result

Each MX-target IP is shown as a row, with a column per blocklist zone. Green ('clean') means the IP is not currently listed on that zone. Red ('listed') means the IP appears in the zone — click through for details and the operator's reason code. The aggregate severity at the top reflects the worst single listing across all rows: any listing on a high-impact zone like Spamhaus ZEN downgrades the whole result. UCEPROTECT L1/L2 are common false-positive sources because they list entire ASN ranges; weight them less heavily than per-IP zones. Multiple zones agreeing on a listing is a stronger signal than one zone alone. Mail providers like Google or Microsoft do not publish their internal blocklists; receivers may filter you to spam without your IP appearing on any public DNSBL.

Common failures

IP listed on Spamhaus ZEN: the highest-impact public listing. Most receivers consult ZEN and treat listings as strong filtering signals. Identify the listing reason in Spamhaus's lookup tool and submit the documented delisting request once the cause is fixed. UCEPROTECT L1 listing on a shared cloud IP: UCEPROTECT often lists IP ranges (L1) belonging to cloud providers like AWS, Azure, GCP. If your IP is in such a range, this listing may be unavoidable in the short term — switch to a dedicated mail-sending IP from a deliverability vendor (Postmark, SendGrid, Mailgun, Resend) instead of relying on raw cloud IPs. Reverse DNS missing or inconsistent: not directly a blocklist failure, but most DNSBLs and major receivers expect outbound mail IPs to have valid reverse DNS matching the HELO/EHLO hostname. Compromised account or open relay: a compromise causes an IP to send spam, which causes listings within hours. Investigate sending logs immediately, rotate credentials, and submit delisting requests after fixing the root cause. Old listing from previous owner: shared/reused IPs sometimes carry forward listings from a prior tenant. Most blocklists have a documented self-removal flow once you can demonstrate cleanup. IPv6-only mail host: per accepted-limitation L2, our blacklist coverage is IPv4-only — IPv6-only domains will show 'unsupported' rather than a real result.

What this does not prove

A clean public-blocklist result does not guarantee inbox placement. Major receivers (Gmail, Outlook, Yahoo) maintain internal reputation systems separate from public DNSBLs, and your domain or IP can be filtered to spam by those systems even with a perfectly clean public-blocklist record. Conversely, a single listing on a low-trust zone may have minimal impact on real-world delivery. We only check publicly queryable DNSBL zones; commercial subscription-only zones (Cloudmark, Symantec, etc.) are not queried. End-to-end deliverability requires real test sends and reading the receiver's response codes.

Common questions

Why is my domain blacklisted?

Common causes: (1) the IP sent spam (compromised account, misconfigured forwarder, or actual abuse); (2) the IP is shared with other senders behaving badly (cloud-provider ranges); (3) the IP was previously used by a spammer (carry-forward listing); (4) excessive bounce or complaint rates triggered automatic listing. Identify the listing reason on the operator's site, fix the root cause, then submit the documented delisting request.

Can I be blacklisted without knowing?

Yes — listings happen automatically based on observed traffic. You will not receive notification from most blocklist operators. The first sign is usually a spike in mail-rejection bounces or customer reports of missing email. Periodic blocklist checks are part of routine email-infrastructure hygiene.

How long does it take to get off a blacklist?

Varies by operator. Spamhaus and SpamCop typically remove within 24-72 hours of a documented self-removal request, provided the cause is fixed. Some operators auto-expire listings after a fixed period (often 7-14 days) if no further bad traffic is observed. UCEPROTECT range-based listings (L2/L3) usually require contacting the IP-range owner, not just yourself.

How do I unblock a blacklisted email?

Identify which blocklist is causing the rejection (the receiver's bounce message usually names the blocklist or includes the URL). Visit that blocklist's lookup tool, find your IP, follow the documented self-removal flow (often a form requiring you to confirm the cause is fixed). For range-based listings, contact your IP provider — you cannot delist a range you do not own.