Mail blocklist (DNSBL) check
We resolve your MX hosts and your website address, then ask the main public anti-spam lists whether those addresses are listed, and why.
Try: google.com · wikipedia.org · github.com · elpais.com
A listing is not the end of the world
Every list publishes its own delisting form, and most honest listings disappear once the cause is fixed: an open relay, a compromised mailbox, a shared address at a cheap hosting provider, or a form on your site that lets anyone send mail.
Queries are sent from our servers over plain DNS. Some lists refuse queries that arrive through large public resolvers and answer with an error code instead of a verdict; those answers are discarded rather than reported as a listing.
Before asking for delisting
Make sure the address has a PTR record that matches its host name, that SPF and DKIM pass, and that DMARC is at least in quarantine. Otherwise you will be listed again within days.