Blacklist status

This takes the addresses behind the domain's MX records and queries them against a set of DNS blocklists — Spamhaus ZEN, SpamCop, Barracuda, PSBL and Spam Eating Monkey among them — plus domain-based lists for the domain itself. Results are cached for an hour and keyed by address rather than by domain, so a hundred domains sharing one host cost one lookup.

The thing to understand before acting on it: MX records name the servers that receive your mail, and those are frequently but not always the servers that send it. A listing on a receiving address does not by itself affect your outbound deliverability. If your outbound mail leaves by another route — a relay, an ESP, an application server — those are the addresses that matter for delivery, and they are not visible from your DNS.

A refused query is reported separately and deliberately. Spamhaus and others answer 127.255.255.252 through 127.255.255.254 when a query arrives via a public resolver or the querier is over quota, and reading one of those as a listing would tell a blameless domain owner they are blocklisted. That case is surfaced as unmeasured — neither clean nor listed.

The lists do not carry equal weight with receivers. A Spamhaus ZEN listing is acted on by a very large share of the internet; some of the smaller lists are used by few receivers and are noisier. Read a single listing on an obscure list differently from one on the list everybody uses.

Work out whose address it is first. If the MX belongs to a mail provider, the listing is theirs to resolve and there is usually nothing for you to do.

Fix the cause before requesting delisting. The usual ones are a compromised mailbox sending spam through your relay, an open relay or an application form that will send mail to any address it is given, and a marketing send to a list that was not opted in. Delisting without fixing it gets you relisted, and repeat listings are harder to clear.

Use each list's own removal process — the report links straight to them. Most are automatic and quick for a first listing.

Then get visibility on the addresses that actually send. DMARC aggregate reports name the sources sending as your domain, and feedback loops from the large mailbox providers report complaints. Both tell you about a problem earlier than a blocklist does.