DNS Doctor (https://dnsdoctor.dev) — DMARC monitoring plus SPF, DKIM and DMARC diagnostics for any domain. Scan email authentication, find SPF lookup-limit problems, check DKIM and DMARC, generate validated DMARC records, monitor DMARC RUA reports and new senders, and move from p=none to quarantine on a scan's evidence and to reject on report evidence. Free domain scans and a free monitoring trial. Every DNS change is human-approved. Fix records are generated deterministically and RFC-validated, never guessed by AI; SPF is diagnosed, never rewritten. Twenty tools: scan a domain (SPF, DKIM, DMARC, MX, DNS health, blacklists, domain and TLS expiry), read the stored report, look up a domain's registration (registrar, expiry, nameservers, locks), build a validated DMARC upgrade or a DMARC record from scratch, validate a pasted DMARC record, count SPF lookups, audit SPF includes, check a DKIM selector, check a record on the domain's own nameservers, check global propagation from six vantage points, check reverse DNS, parse a DMARC aggregate report, build the hardening pack for a non-sending domain, hand the owner a monitoring sign-up link, and for signed-in operators read the monitoring alert log and the enforcement-readiness verdict. Three account tools add a domain to monitoring, run the ownership check and read the records to publish; today they hand the owner the same sign-up link. The assistant never signs the user in, never emails on their behalf, and never applies a DNS change: it explains the findings and presents each record for the human to publish.