The reverse DNS record is also known as the PTR record, pointer record, or IP resolvers.
A PTR is a reverse record for an IP address, which allows an IP to map to a domain, and vice versa. That means you can make hostgator.com point to 10.0.0.1, and make a ptr record so that 10.0.0.1, if checked, would tell you that it belongs to hostgator.com. It lets the receiver of your emails check for possible spoof emails, which will be treated as spam. Without this record, the receiver must rely on guessing if your email might be spam.
Generally, when you have a PTR record, your emails have a better chance to deliver to my inbox instead of my spam folder.
Now what do most mail servers do, if they actually check this?
When the sending server, lets say a VPS, tacocat.hostgator.com for instance, sends an email to gmail, from the address random@somedomain.com, it will connect to the gmail server and tell it "Hello, I'm tacocat.hostgator.com"
Gmail then has the option to either say "What email do you have for me?" or "Let me look into this..."
If it's the latter, Gmail will pull a rDNS record on the ip that tacocat.hostgator.com is connecting from. It does NOT check the domain somedomain.com, that would only occur for reverse user checking, which has nothing to do with rDNS records. (Or if the admin of the mailserver felt especially evil.)
If the rDNS record comes up as tacocat.hostgator.com, then Gmail will be happy.
Additionally, in some cases, if the rDNS comes up as somedomain.com, and somedomain.com points to that IP address, some email servers will accept that, since the mail server ip is able to map back to itself, even if its hostname claim does not match. Do not rely on the external mail server being that smart though.
Times when this is not true, is when exim is configured to send from other IP's, dependent on it's hostname, this can be seen by checking /etc/mailips. Most clients do not have this, and do not need it.
How do I add a PTR record for my HostGator account?
Shared and Reseller:
HostGator has already setup default PTR records for shared and reseller servers by default.
Dedicated and VPS
We can create this record on your domains per request. Just contact us via phone, live chat, or email support@hostgator.com with the domain name.
