DNS
What is Reverse DNS (rDNS)?
The lookup that resolves an IP address back to a hostname, the opposite of normal DNS resolution.
Reverse DNS uses PTR records in the in-addr.arpa (IPv4) or ip6.arpa (IPv6) zones to answer the question of which hostname is at a given IP. Mail servers use it, often alongside a forward lookup, to perform forward-confirmed reverse DNS (FCrDNS), where the PTR hostname must itself resolve back to the same IP. It is configured on the IP owner's side, so senders usually request it from their host or ESP.
Why it matters for cold email
Reverse DNS that matches the sending hostname is a core sender-legitimacy signal, and cold-email IPs without proper rDNS get throttled or blocked by Gmail, Outlook, and others. Verifying FCrDNS is one of the first things to fix when inbox placement is poor on a dedicated IP.
Related terms
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