Reverse DNS
Articles, guides, and in-depth tips for the Reverse DNS — everything you need to get the most out of it.
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How to Read a PTR Record Like a Network Investigator — Email Forensics, ISP Naming Patterns, and FCrDNS
Reverse DNS Is an Assertion, Not a Proof — Here's What FCrDNS Actually Verifies
A PTR record saying "mail.example.com" for an IP doesn't prove that IP is operated by example.com — it proves whoever controls the reverse DNS zone for that IP chose to set that name. Here's the fundamental asymmetry between forward and reverse DNS, why "forward-confirmed reverse DNS" (FCrDNS) provides substantially more confidence than PTR alone, how Google uses FCrDNS to verify Googlebot traffic, and when PTR records are legitimately useful for logging even without cryptographic verification.
Reverse DNS for IPv4 vs IPv6: Why ip6.arpa Delegation Works So Differently from in-addr.arpa
IPv4 and IPv6 reverse DNS use the same in-addr.arpa/ip6.arpa concept — but IPv6's vastly larger address space means most addresses simply don't have PTR records, by practical necessity rather than oversight. Here's how each zone's delegation works, who controls PTR record configuration, and why "no PTR record" is a much more common and unremarkable result for IPv6.
IP Geolocation: How It Works, Why City-Level Accuracy Is Unreliable, and the VPN Problem
IP geolocation is 95–99% accurate at country level and 50–80% accurate at city level — and VPN users are always wrong by design. Here's how geolocation databases work, the legitimate business uses, the VPN problem for geo-dependent services, and what an IP lookup actually reveals beyond location.
Reverse DNS and Email Deliverability: Why Your PTR Record Silently Matters
A missing PTR record silently degrades email deliverability. Here's how forward-confirmed reverse DNS works, why it matters for email authentication, who controls PTR records, and how reverse DNS is used in security investigation.
Reverse DNS Lookup — Translate Any IP Address to Its Hostname
Learn how reverse DNS works, what PTR records reveal about IP addresses, why forward-confirmed reverse DNS matters for email, and how to use a free reverse DNS lookup for security and diagnostics.
