Reverse DNS and hosting multiple domains

[xianaier]

I'm having trouble understanding reverse DNS properly.

From what I understand, rDNS can be used to help verify that an IP address matches a domain name for email. What I don't get is how that works when you have multiple domains from one IP address. If I ask my VPS host to set up rDNS and 123.123.123.123 points to domainA.com, then what about domainB.com, domainC.com and so on?

Am I wrong in assuming that rDNS can only have one domain point to one IP address?

Are there implications for me using a service like Cloudflare for DNS?

[carl owen]

Normally, the mailserver routes the mails of all the domains through the main IP address of the server and the rDNS is pointed to the hostname. And you are right in assuming that rDNS can only have one domain point to one IP address.