We put “unauthenticated” in quotes because having a Reverse DNS record attached to your domain does not automatically guarantee acceptance of email originating from your domain by the recipient’s email server.It’s just that non-matching or generic reverse DNS lookup settings are often rejected out of hand.Having a reverse DNS record for your domain will prevent email originating from your domain from getting immediately rejected.RDNS can also be very useful when tracking down network issues and was the original driving force of RDNS.to 172.20.4.205 Jul 19 morgan dhcpd: unable to add reverse map from 205.4.20.172.

Here is part of the syslog output: Jul 19 morgan dhcpd: Added new forward map from tech-Coordinator.gilman.k12us.

A lesser-known task that DNS performs is determining the hostname from an IPv4 address, commonly called reverse resolution.

This is normally used by servers to find the human-friendly name associated with the IP address.

For example, in IPv4, you could have a /23 network registered with ARIN that is comprised of two /24 delegations.

In this case, you are able to delegate one set of nameservers to the first delegation and another set of nameservers to the second delegation. Occasional users can manage their delegations via ARIN Online, but users who manage a large number of delegations can programmatically modify their delegations using ARIN’s RESTful provisioning system.