smtp; 553 sorry, invalid HELO hostname (#5.7.1)

Hi,
my email server is sending emails to gmail, yahoo and other free email service providers but when i send email to rediffmail.com it gives the following error

smtp; 553 sorry, invalid HELO hostname (#5.7.1)

after looking at the internet for solution it says that this type of error comes when the hostname set inside cpanel doesn't lead to an ip address or is not FQDN but in my case i have checked the hostname and checked if my hostname leads to an ip address on pinging it does

Please recommend

 

Hi,
following is the output of the above command, i have just replaced my sending email id with demo.value@ourownserver.com and rediff email id to demo.value@rediffmail.com and the ip from which i am sending to xxx.xxx.xxx.xxx to keep my info private

Code:

2016-01-04 05:34:06 1aG1ee-000383-SW ** demo.value@rediffmail.com R=dkim_loo                                                                                        kuphost T=dkim_remote_smtp H=mx.rediffmail.rediff.akadns.net [202.137.234.30] X=                                                                                        TLSv1:DHE-RSA-AES256-SHA:256 CV=no: SMTP error from remote mail server after RCP                                                                                        T TO:<demo.value@rediffmail.com>: 553 sorry, invalid HELO hostname (#5.7.1)
2016-01-04 05:34:06 1aG1ee-000383-SW Completed