Reverse DNS record can't point to Domain name but it can point to IP [closed]

I am using parallels plesk for hosting my websites,

Some days ago I tried to send emails from my mail server and the mails were going to spam,So i tried spam assassin to detect whats wrong. Here is output of that:

 pts rule name               description
---- ---------------------- --------------------------------------------------
 0.0 URIBL_BLOCKED          ADMINISTRATOR NOTICE: The query to URIBL was blocked.
                            See
                            http://wiki.apache.org/spamassassin/DnsBlocklists#dnsbl-block
                             for more information.
                            [URIs: xyz.org]
 0.0 HTML_MESSAGE           BODY: HTML included in message
 1.3 RDNS_NONE              Delivered to internal network by a host with no rDNS 

So as per that I had come to know that I need to setup an RDNS for xyz.org, But it can't be done by my side; It should be done by my ISP.

So i had contacted them and told them to set an RDNS for my domain(xyz.org) on IP(say1.2.3.4).

That is It should output something like:

4.3.2.1.in-addr.arpa. TTL(86400) IN PTR smtp.xyz.org.

But Here is what they are saying to me: Reverse DNS record can't point to Domain name but it can point to entire IP

What is that?? I mean why can't it point to my domain name? it is right now pointing to somehing like: pingaworks.managedns.org.? Is that why I'm getting spam assassins error? Is there any simple way to create RDNS for your VPN using parallels plesk? also I'm the admin of server.

Also after further reading I had come to know that, RDNS is required if you're planning to have a mail server afterwards(and yes I'm planning for it); What should I do now?

BUT

I don't understand what my ISP is saying. Hope experts here will help me. Please.

Thanks in advance.

MOST Importantly:

How To setup RDNS for domain name?

I had wasted 96hrs on this, but without success.

Solution 1:

Reverse DNS points an IP to a domain name. An ISP/Hosting company should own the IP range, and it should be no problem at all for them to create a reverse DNS entry for your IP, unless it's not just your IP (you're on shared hosting).

Should that be the case, you are not going to get anywhere. Your ISP/Hosting probably can get you your own individual IP, but I'll imagine you will be paying more for it.