VPS
Setting reverse DNS (PTR)
Point your VPS IP addresses back at your hostname, e.g. for mail servers.
Create the forward record first
Add an A record (IPv4) or AAAA record (IPv6) for your hostname pointing at the VPS address, and wait for it to propagate.
Set the PTR
Open the Network tab on your VPS, enter the hostname next to the address and save. We check that the hostname resolves to the address before changing reverse DNS.