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Reverse DNS Lookup
PTR record lookup for IPv4 and IPv6 addresses, plus forward-confirmation: whether the returned hostname resolves back to the same IP. Mail servers without forward-confirmed reverse DNS get their outbound mail distrusted or refused.
PTR records live in the address owner's zone (usually the ISP or cloud provider), not the domain owner's, so a missing or generic PTR is fixed through whoever owns the IP block. Lookups run read-only through Cloudflare's public resolver; nothing is stored or logged.