Glossary
Reverse DNS (PTR)
Reverse DNS resolves an IP address back to a hostname using a PTR record, commonly checked to verify mail servers and identify hosts.
Reverse DNS (rDNS) is the inverse of normal resolution: instead of name to ip-address, it maps an IP back to a hostname. The lookup uses a PTR record stored in a special reverse zone (in-addr.arpa for IPv4, ip6.arpa for IPv6).
How it works
For 93.184.216.34, the resolver queries 34.216.184.93.in-addr.arpa for its PTR record, which returns a hostname such as server.example.com.
Why it matters for hosting
- Email deliverability — receiving mail servers often reject or distrust messages from IPs whose PTR does not match a forward
a-record(forward-confirmed reverse DNS). Setting correct rDNS is essential for self-hosted mail. - Identification — rDNS frequently reveals the
datacenteror provider behind an IP.
Crucially, PTR records are controlled by whoever owns the IP block (the asn operator or host), not by the domain owner — so you usually request rDNS changes through your hosting provider.
See also
IP Address
An IP address is the unique numeric label assigned to each device on a network, used to route data to the right destination across the internet.
ASN (Autonomous System Number)
An ASN is a unique number identifying a network of IP ranges under one operator, used by BGP to route traffic across the internet.
MX Record
An MX record is the DNS entry that directs a domain’s email to the correct mail servers, with priority values choosing primary and backups.
DNS (Domain Name System)
DNS is the internet phone book that translates human-readable domain names like example.com into the IP addresses computers use to connect.