No reverse DNS, MX host should have rDNS - RFC1912 2.1

No reverse DNS, MX host should have rDNS - RFC1912 2.1

Hi there, 

I have been facing problem sending emails. Everytime we send email it goes to SPAM in recipient side. Specially when i use zoho from office. MX tools says our IP is 

Added to SPAMCANNIBAL
And reason from Spam cannibal is " no reverse DNS, MX host should have rDNS - RFC1912 2.1" 

could anyone help me how to fix this as we are loosing clients due to our email delivery. 

Thank you