Pro move: type dmarc:yourdomain.com or blacklist:1.2.3.4 straight into the box — it switches tools for you.
About this tool. Opens a raw TCP connection to any host and port from our edge and times the handshake. Handy for checking whether a service is reachable at all. Ports 80/443 are reserved for the HTTP checks, and port 25 is blocked platform-wide — the SMTP tool covers mail servers.