Merhaba,
Windows hyperV üzerinde çalışan bir Centos sunucum var (WHM kurulu) bu sunucudaki mail adresinden Gmail'e mail atamıyorum geriye böyle bir mail dönüyor.

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

  serefseven@gmail.com
    host gmail-smtp-in.l.google.com [66.102.1.26]
    SMTP error from remote mail server after end of data:
    550-5.7.1 [185.124.86.138] The IP address sending this message does not have a
    550-5.7.1 PTR record setup. As a policy, Gmail does not accept messages from
    550-5.7.1 IPs with missing PTR records. Please visit
    550-5.7.1  https://support.google.com/mail/answer/81126#authentication for more
    550 5.7.1 information. y187si26143569wmc.112 - gsmtp
Reporting-MTA: dns; ln1.postoflscell.com

Action: failed
Final-Recipient: rfc822;serefseven@gmail.com
Status: 5.0.0
Remote-MTA: dns; gmail-smtp-in.l.google.com
Diagnostic-Code: smtp; 550-5.7.1 [185.124.86.138] The IP address sending this message does not have a
 550-5.7.1 PTR record setup. As a policy, Gmail does not accept messages from
 550-5.7.1 IPs with missing PTR records. Please visit
 550-5.7.1  https://support.google.com/mail/answer/81126#authentication for more
 550 5.7.1 information. y187si26143569wmc.112 - gsmtp
mxtoolbox.com dan smtp test yaptığımda bu uyarıları alıyorum

SMTP Reverse DNS Mismatch	Reverse DNS does not contain the hostname

SMTP Banner Check	Reverse DNS does not match SMTP Banner	 

SMTP TLS	Warning - Does not support TLS.

SMTP Transaction Time	15.485 seconds - Not good! on Transaction Time	 

SMTP Valid Hostname	OK - Reverse DNS is a valid Hostname	

SMTP Connection Time	0 seconds - Good on Connection time	

SMTP Open Relay	OK - Not an open relay.
bu sorunu nasıl çözebilirim? neden kaynaklanıyor?