DNS & Glossary

Reverse DNS (rDNS)

Looking up the hostname for an IP address, the inverse of normal resolution. Mail servers and security tools rely on it, especially forward-confirmed reverse DNS.

What it is

Reverse DNS uses PTR records in the in-addr.arpa / ip6.arpa zones to map an address to a name. Forward-Confirmed reverse DNS (FCrDNS) — where the name's forward record points back to the same IP — is what mail servers check to judge sender legitimacy.

Why it matters

  • Correct rDNS is important for email deliverability and reputation.
  • It makes logs and diagnostics human-readable.

Common mistakes

  • Missing PTR or a PTR whose forward record does not match, hurting mail reputation.
  • Expecting to control rDNS in your own zone when the IP owner sets it.

How WebInspect checks this

  • The Network Inspector performs reverse lookups and forward-confirmation checks and reports the result.