Is Reverse DNS Necessary?
Some junior DNS administrators configure forward DNS and forget to configure reverse DNS. When they do this, some things work fine. Internet web browsing, for example, works great. However, not everything works. Reverse DNS is required by some Internet protocols and by extensions to some other Internet protocols. Without reverse DNS, you will experience trouble with r-commands, IRC, some SMTP servers, most enterprise management systems, and many network backup systems. Troubleshooting problems caused by faulty or non-existant reverse DNS can take considerable time and effort. It is much better to ensure that reverse DNS is configured correctly from the beginning.