Use when you need to check whether a domain is protected against email spoofing or set up for deliverability: reads MX (and guesses the mail provider), SPF (qualifier, lookup count), DMARC (policy, pct, report addresses), DKIM on common selectors, MTA-STS (record and policy mode), TLS-RPT and BIMI, and returns a grade A-F, a score and a list of concrete issues. Paid tool: x402 USDC on Base, $0.003 per successful call; call without payment to receive the PaymentRequired object.