How to solve Zimbra error "message does not meet IPv6 sending guidelines regarding PTR"

As we are using MTA hence i have logged in to MTA server and checked postfix inet protocol and found it was enabled for all

Log into your server SSH and run the following commands:

root@mta:/etc/postfix# postconf inet_protocols

inet_protocols = all

root@mta:/etc/postfix# postconf inet_protocols=ipv4

root@mta:/etc/postfix# postconf inet_protocols

inet_protocols = ipv4

root@mta:/etc/postfix# service postfix restart

root@mta:/etc/postfix#

Thank you!