What is a reverse DNS entry (rDNS) and why do I need it?
Posted by Help Desk (6), Last modified by NOC Desk Monitors on 07 August 2018 11:42 AM
A DNS normally consists of ‘Forward’ lookups such as A records. An example of this would be the domain name ‘helpdesk.hostnetworks.com’ has the A record of 202.174.100.9.

A Reverse DNS entry, known as a PTR (Pointer) record does the opposite and matches the IP to the domain name.
So using the above example, performing a reverse DNS whois lookup of 202.174.00.9 results in helpdesk.hostnetworks.com.

This is found by asking the name servers responsible for the IP address.

For this to work a forward record must exist and match the PTR record. If the PTR record does not match the Forward record then errors will occur.


Why do I need a rDNS entry?
Just about every mail server on the internet uses a basic check to verify that the sender is legit and isn’t spam. It does this by checking that a rDNS entry exists for the IP sending the email. If it doesn’t the mail will bounce.

This is only required on the IP sending email and isn’t required for every IP address you may have with your service.


How to get an Reverse DNS PTR Record added?
Simply lodge a ticket in the helpdesk asking for a PTR record to be created for x.x.x.x (IP Address) with the name X.X.X (A valid A record you have setup for that IP).
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