Online network diagnostics — DNS, GeoIP, ping, SSL, Whois, HTTP headers, and more. No login required.
The report gathers the public signals mail filters and browsers weigh: whether the domain or address is on the public blacklists, how the domain protects its mail (SPF, DMARC, MX), whether its HTTPS certificate is valid, how long it has been registered, and for an address whether it has a reverse DNS name that points back. Each finding says what was seen and what it costs; the score is 100 minus those costs.