Through the classic DNS system, one can resolve a hostname or a domainname to an ip address. This way www.google.com is translated to 74.125.77.103. The server setup to listen for that ip address will serve the website.

Through “Reverse DNS“,or rDNS, you can become the opposite;you can look up the hostname through the ip address. This way the ip address translates itself, through reverse DNS, to “ew-in-f103.google.com”.

At first there doesn’t seem to be a practical advantage to setup reverse dns. Because we can almost always reach the wanted destination through hostname or domainname, as we don’t enter ip addresses in the address bar of our browser, but domain names.

However, reverse DNS is used intensively to verify email traffic on its authenticity. A mailserver should be configured with an FQDN – Fully Qualified Domain Name. Thus the mailserver identifies itself to other systems.
This way, when a mailserver identifies itself as “smtp.nucleus.be”, the recipient is able to verify this.

Subsequently, using the normal DNS lookup, “smtp.nucleus.be” is translated to “195.207.48.20”. The extra verification occurs through reverse DNS. This way one can verify whether the mailserver identifying itself as “smtp.nucleus.be”, is the one he claims to be. A reverse lookup is performed on “195.207.48.20”, translating itself to “smtp.nucleus.be”.

A spamserver identifying itself as “smtp.nucleus.be” while sending mail from an other ip address will be detected using reverse DNS. The message will not be delivered to the recipient domain but will probably be marked as “spam“.
Ofcourse this depends on the spamfilter; not every spamfilter has this option enabled.

Reverse DNS records, also called PTR records, can only be managed through the administrator of the ip addresses, i.e. the ISP.
If you have a server hosted at Nucleus, you can request reverse DNS by mailing tosupport@nucleus.be. We are happy to set this up for you.

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