You can think of the PTR record as an opposite of the A record. While the A record points a domain name to an IP address, the PTR record resolves the IP address to a domain/hostname.
PTR records are used for the reverse DNS (Domain Name System) lookup. Using the IP address you can get the associated domain/hostname. An A record should exist for every PTR record.
The usage of a reverse DNS setup for a mail server is a good solution. Some external mail exchange servers make reverse DNS lookups before accepting messages originating from your mail server.
You can check whether there is a PTR record set for a defined IP address. The syntax of the commands on a Linux OS are:
dig -x IP
or
host IP
For example, you can run the following commands in your Linux terminal:
dig -x 96.31.83.163
and the result would be:
; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.30.rc1.el6_6.1 <<>> -x 96.31.83.163
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 59024
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;163.83.31.96.in-addr.arpa. IN PTR
;; ANSWER SECTION:
163.83.31.96.in-addr.arpa. 15161 IN PTR enterprisevpssolutions.com.
;; Query time: 7 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Mon Jan 5 21:48:31 2015
;; MSG SIZE rcvd: 83
or
host 96.31.83.163
and the result would be:
163.83.31.96.in-addr.arpa domain name pointer enterprisevpssolutions.com.
The corresponding command under the Windows OS command prompt is:
nslookup IP
The reverse DNS lookup for IP version 4 uses a special domain – in-addr.arpa., while the lookup towards IPs version 6 uses ip6.arpa..
Detailed explanation of the reverse DNS lookup can be found in the following article:
http://en.wikipedia.org/wiki/Reverse_DNS_lookup
The rDNS service is provided for free and it can be requested by submitting a ticket to our support team from the client portal. There can be only one PTR record per IP address. Multiple PTR records can not be set for one IP.
