your provider sets the rDNS you'd need to contact them to give the rDNS pointer a name.
i can set the rdns through solusVM cp.
i found it is a problem with /etc/hosts i modified it like below and got working. but if i rebooted it get reverted back to the old one.
# Auto-generated hostname. Please do not remove this comment.
host file is controlled by some process and when i searched for this, it said to be dealt with openvz.
what i did to solve it,
Edited the line in /etc/hosts like this
127.0.0.1 xx.example.com xx localhost localhost.localdomain
Locked the host file from auto modification
chattr +i /etc/hosts
Rebooted. Done