Check email syntax, DNS and MX records, disposable providers, role addresses, free providers and SPF/DMARC presence. Returns likely-deliverable, risky, undeliverable or invalid with reasons. No message is sent and the mail server is not contacted. These are DNS and syntax signals, not proof that a mailbox exists or accepts delivery. Use before sending mail or saving a signup. Example: address=support@cloudflare.com. Price $0.003/call via x402 USDC or a card key (/credits), first 25 free; failed calls free. Reads or computes only and changes nothing; each call is charged, so repeats are not free.