Unlike a normal DNS lookup, which translates a domain name into an IP address, Reverse DNS (rDNS) translates an IP address back into a hostname.
Reverse DNS is implemented using PTR (Pointer) records.
Forward DNS:
example.com
│
▼
93.184.216.34
Reverse DNS:
93.184.216.34
│
▼
example.com
Forward DNS uses A or AAAA records.
Reverse DNS uses PTR records.
Reverse DNS helps verify that an IP address belongs to a particular hostname.
Many services use PTR records to:
Reverse DNS uses a special namespace.
For IPv4:
93.184.216.34 becomes 34.216.184.93.in-addr.arpa
A resolver queries that name for a PTR record.
Example:
34.216.184.93.in-addr.arpa PTR example.com
IPv6 uses the ip6.arpa domain.
Example:
2001:db8::1 ↓ ...ip6.arpa
The lookup principle is the same as IPv4.
Unlike normal DNS records, PTR records are not controlled by the domain owner.
PTR records are controlled by the owner of the IP address.
Usually this is:
Therefore, changing a PTR record often requires contacting your hosting provider.
Many mail servers perform an additional check called Forward-Confirmed Reverse DNS.
The process is:
IP Address
│
▼
PTR Record
mail.example.com
│
▼
A Record
mail.example.com
│
▼
Same IP Address
If the forward lookup returns the original IP address, the reverse DNS is considered consistent.
Many email providers, including Gmail, Outlook, and Yahoo, verify the sending server's PTR record.
If a mail server has:
messages may be rejected or marked as spam.
Typical error:
550-5.7.25 The sending IP does not have a PTR record.
This is one of the most common email configuration problems.
Suppose your mail server is:
mail.example.com A Record mail.example.com ↓ 203.0.113.15
The corresponding PTR record should be:
203.0.113.15 PTR mail.example.com
This creates a consistent forward and reverse mapping.
PTR records are commonly used for:
Most websites themselves do not require PTR records.
A DNS lookup for a PTR record differs from an A record lookup.
Instead of querying a hostname:
example.com
the resolver queries the reversed IP under in-addr.arpa (IPv4) or ip6.arpa (IPv6).
Telenegar DNS Check supports PTR lookups.
Given an IPv4 or IPv6 address, the tool can display:
This is useful for diagnosing: