Here I am trying to send mail using Java Mail API. When I am trying to test this to send mail to users from my office public IP address, it works but when I deploy my application to main server then it fails to send the mail, simply getting error message "Relaying denied. IP name lookup failed [IP-Address]" Here all articles says you have to allow relay from certain hosts is to add those hosts to /etc/mail/local-host-names You just need to make those changes to the mailserver that is running on your droplet. Can you guys help me , where I have to configure this ??