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.
Why you need a PTR records?
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).
Here is an example of a PTR record for 111.222.333.444 would look like:
444.333.222.111.in-addr.arpa. 33692 IN PTR host.example.com.
This example of a PTR record for an IPv6 address shows the nibble format of the reverse of Google's IPv6 DNS Server 2001:4860:4860::8888.
8.8.8.8.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.6.8.4.0.6.8.4.1.0.0.2.ip6.arpa. 86400IN PTR google-public-dns-a.google.com.
The command line tool dig with the -x flag can be used to look up the reverse DNS name of an IP address.
Here is an example of a dig command. The +short is appended to reduce the output to the reverse DNS name.
- dig -x 8.8.4.4 +short
The output for the dig command above will be the domain name in the PTR record for the IP address:
google-public-dns-b.google.com.
Servers on the Internet use PTR records to place domain names within log entries, make informed spam handling decisions, and display easy-to-read details about other devices.
Most commonly-used email servers will look up the PTR record of an IP address it receives email from. If the source IP address does not have a PTR record associated with it, the emails being sent may be treated as spam and rejected. It is not important that the FQDN in the PTR matches the domain name of the email being sent. What is important is that there is a valid PTR record with a corresponding and matching forward A record.
Most providers offering dedicated servers or VPS services will give customers the ability to set a PTR record for their IP address. SimpleCloudHosting will automatically assign the PTR record of any Droplet when the Droplet is named with a domain name. The Droplet name is assigned during creation and can be edited later using the settings page of the Droplet control panel.
Note: It is important that the FQDN in the PTR record has a corresponding and matching forward A record. Example: 111.222.333.444 has a PTR of server.example.com and server.example.com is an A record that points to 111.222.333.444.
Alert: For Control Panel Help & Tutorials, click here: Panel Tutorials
