You can configure the reverse DNS record (PTR) for the Hetzner server in the control panel robot.your-server.de
Clicking on the left “Servers” – selecting the server, and clicking on the IP address of the north will appear the input field “Reverse DNS”, where it should be specified.
After adjustment, in my practice, the changes took effect during the day.
Configure the PTR record on the DNS server
At Hetzner, I recently purchased a second IP address for my server for sending mail as, unfortunately, the primary IP address had a bad sender reputation.
Is it OK to to have the same reverse DNS entry for both IP addresses?