PTR. Set up PTR record
A PTR record maps an IP address to a domain name as opposed to an A record which points a domain name to an IP address.
What is PTR record used for?
Usually, PTR records are used for outbound email servers since incoming mail servers might not even consider accepting a message from an IP address which does not identify itself with a PTR record. If there is a PTR record and it matches the domain name from which an email has been received it is one of the ways not to get an email into the spam folder.
How to set it up?
Choose a server in the Control Panel and click on IP addresses.
Choose the IP address for which you want to set or change a PTR record and click on Edit.
In a new window put a domain name into Domain field. The PTR record will be created automatically.