reverse DNS

Reverse DNS (rDNS) maps an IP address back to a hostname, the opposite of normal DNS lookup. You query a PTR record instead of an A record. Mail servers use it heavily: they check if incoming mail's source IP resolves to a legitimate hostname, and if the hostname resolves back to that same IP (forward confirmation). If it fails, spam filters flag you harder. Running a bulletproof domain means your mail infrastructure needs solid reverse DNS—sloppy setup kills deliverability fast. Some hosting providers give you free rDNS setup; others charge or refuse anonymous customers. This is why offshore and crypto-friendly hosts matter: they don't demand KYC just to point a PTR record. Reverse DNS doesn't hide your IP, but it does validate it. Important for anyone sending mail at scale, running mail servers, or operating infrastructure that doesn't want to look like a botnet.