What is Reverse DNS (rDNS)?
Reverse DNS (rDNS) maps an IP address to a hostname. It is the opposite of forward DNS (which maps hostname to IP).
Forward: mail.tidalmail.com → 192.0.2.1
Reverse: 192.0.2.1 → mail.tidalmail.com
How it works: PTR records in special reverse DNS zones (in-addr.arpa for IPv4) store the mapping.
Email importance:
- Receivers check if sending IP has valid reverse DNS
- Missing or mismatched rDNS is a spam signal
- Legitimate mail servers always have proper rDNS
Reverse DNS proves the IP owner has configured it properly. It is a basic trust indicator.
Verifying a ship's registration by looking up its hull number rather than its name.
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