Pro move: type dmarc:yourdomain.com or blacklist:1.2.3.4 straight into the box — it switches tools for you.
About this tool. MX records tell the world which mail servers accept email for a domain. If they're missing or wrong, email simply doesn't arrive. This lookup lists every MX host in priority order, resolves each one to its IP addresses, and tells you which provider is behind it in plain English.