Grade a domain's email-authentication posture (SPF, DKIM, DMARC, BIMI, MX) and tell an agent whether the sender can be spoofed. Returns an A–F grade, a `spoofable` flag, the parsed DMARC policy and SPF qualifier, and specific misconfiguration issues. Use to judge a sender domain before trusting an email, or to confirm your own outreach domain won't be silently rejected by Gmail/Yahoo/Microsoft's 2026 authentication rules.