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.
While in the domain DNS zone the hostname is pointed to an IP address, using the reverse zone allows to point an IP address to a hostname.
In the Reverse DNS zone, you need to use a PTR Record. The PTR Record resolves the IP address to a domain/hostname.
PTR records provides trust that the given hostname or a domain are connected to the IP address. The PTR records are must have for outgoing mail servers, because most of the mail providers reject or mark as spam messages received by mail servers without valid reverse dns configuration (missing PTR or missmatch A record for the hostname).
In order to create a PTR record, at first need to be created a Reverse DNS zone (read more about the reverse dns zones here). The reverse DNS zone depends on the size of your IP network. In our example we will use an IPv4 /24 network. In the /24 network, you have 255 unique IP addresses. For an example, if our network is 192.168.0.0/24, the available IPs in this network are from 192.168.0.1 to 192.168.0.255 and our reverse zone has following format: 0.168.192.in-addr.arpa
In order to create a reverse DNS zone go to the Control Panel, click on the Add new zone button and choose Master Reverse DNS zone and fill the reverse zone name of your IP network. In our case this is 0.168.192.in-addr.arpa
Now in our reverse zone 0.168.192.in-addr.arpa we can add PTR records for each IP from the network. From the button "Add new record" we can add new PTR record and here are few examples for the first two IP address:
Points to: hostname1.example.com
Points to: hostname2.example.com
Here is a video tutorial how to add the PTR records step by step:
The PTR records has the following look in the Control Panel:
After creating the PTR record, make sure that the hosts have corresponding A records. In our example, hostname1.example.com must be with A record pointed to 192.168.0.1 and hostname2.example.com with 192.168.0.2
To be completed the reverse DNS configuration, you need to change the name servers of your reverse zone at your IP provider or ask him to assist you with the modification. In our case, there must be configured NS records at the IP provider pointed to the name servers listed at the dashboard of your control panel.
ClouDNS supports Reverse DNS zones both for IPv4 and IPv6 networks. Just write to our technical support, if you need any assistance with the configuration of the Reverse DNS and PTR records for your network and IPs.