Email validation API: RFC-style syntax check plus live MX-record lookup (with RFC 5321 A-record fallback) over DNS-over-HTTPS — no third-party service, nothing stored. Returns parsed domain, sorted MX hosts, and a 'deliverable' flag meaning DNS will accept mail for the domain — it does NOT verify the mailbox exists. Use for lead cleaning, signup validation, and contact verification by agents. Cached up to 1 hour per address.