Q:

550 No RDNS entry for my ip (in reply to RCPT TO command)

Some recipients are making RDNS verification to my mail server and being refused.
I have a CentOS VPS with my website and mail server for my business.
Is there anything wrong here? I can provice my postfix configs as well. Any help pointing me in the right direction would be really appreciated
Undelivered Mail Returned to Sender This is the mail system at host mail.domain.com.
I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<user@destinationdomain.com>: host mail.[destination_ip] said: 550 No
    RDNS entry for 100.200.300.400 (in reply to RCPT TO command)

/etc/named.conf
zone "300.200.100.in-addr.arpa" {
type master;
file "/var/named/300.200.100.in-addr.arpa"
};

/var/named/300.200.100.in-addr.arpa
$TTL 3600
@          IN SOA clark.ns.cloudflare.com. elma.ns.cloudflare.com. (
              2012020801       ; Serial
              21600             ; refresh
              3600              ; retry
              3600000           ; expire
              86400 )           ; minimum

           IN  NS clark.ns.cloudflare.com.
           IN  NS elma.ns.cloudflare.com.

; ----------- ENREGISTREMENTS -----------
$ORIGIN 300.200.100.in-addr.arpa.
400                      IN PTR                  domain.com.
; ----------- ENREGISTREMENTS SPECIAUX -----------

On cloudflare I have this relevant entries:
A mail points to VPS IP
MX domain.com mail handled by domain.com
TXT _dmarc v=DMARC1;p=none;rua=mailto:user@domain.com;
TXT domain.com v=spf1 mx a ~all

Domain being used for IMAP and SMTP
mail.domain.com

A:

You cannot control the reverse DNS records for the VPS's IP address directly yourself. Your VPS provider controls these records. Contact that provider for instructions on how to set the reverse DNS record.

