CaptainDNS lets you diagnose DNS zones and audit email security records, SPF, DKIM, DMARC, MTA-STS, BIMI and DNSSEC, for free. Unlike basic DNS checkers, it covers the full resolution chain across 18 resolvers on 4 continents. Already used to analyse 48K+ domains, it gives developers and IT teams actionable diagnostics in one place, without switching between multiple tools.