PTR records in brief
Server or hosting owners may have come across the term PTR record. In short, it is reverse DNS. When a domain is added to a server, an A record is created at the domain name registrar linking the domain name to an IP address, while PTR works the other way around: it links the IP address to the domain.
When a PTR record is needed
You need to set up reverse DNS for your sites if you plan to send mail from the server with the sender shown as @vashdomen.com. Most modern mail services check each message against a number of criteria and then decide whether to place it in the SPAM folder or the INBOX. And one of the key factors in deciding which folder an incoming message lands in is whether the domain has a PTR record.
How and where to set up a PTR record
To set up a PTR record, contact the support service of the hosting provider from which you rent your dedicated or virtual server. Provide your IP address and the domain the rule should be created for. Usually everything is up and running within 30 minutes (after support replies).
How to check whether an IP address has a PTR record
Open the command prompt and enter the command:
#nslookup 135.45.456.23
where 135.45.456.23 is your IP.
If the record is working, this command should return the domain name in response.
You can also check using online services, for example 2whois.ru