Reverse DNS is not a valid hostname. What is the reason?

Question

Mail server

Vps - Hetzner Centos 7
Mail server on ISPmanager 5 Lite.



hostname: spelled correctly "gud-lid"
IP: spelled correctly "gud-lid"

Tech ISP support is at a loss to answer.

Problem: Reverse DNS is not a valid Hostname

Where to look for the cause?

Answer 1

You have 116.203.81.234 = gud-lid.ru in the reverse zone, but it should be mail.gud-lid.ru
Do nslookup 116.203.81.234 and see for yourself.