It is useful for outgoing mail servers. Most mail servers check the PTR record of the IP address of the server from which the email came before making a decision to put an email in the "Inbox" or reject it as SPAM. If there is this record and it matches the name of the domain from which the message came, it will be one of the facts for a positive decision (that the message is not SPAM).
In order to add a PTR record you need to do the following steps
Go to Settings menu of your order and in section IPv4/IPv6 → rDNS and press the button Edit.
Enter the Domain Name and click the Checkbox to save.
To see the PTR record:
OS Windows you need to open the command line Start → Run → cmd and type in:
nslookup -type=PTR ip-address
On Unix-like systems, open a terminal Ctrl+Alt+T and run the command:
dig -x ip-address
If you have configuration difficulties or have additional questions, you can always contact our support team via ticket system.