The part that you will be adding is: -f'user@domain.com'
This method works because the php mail function calls sendmail (a program on the server) directly using the path defined in your php.ini. Placing the -f flag here allows us to work directly with sendmail without PHP getting in the way. Passing a "From" header to the php mail function will override the -f flag set in your php.ini.
For scripts such as Joomla and Wordpress, you will need to follow their documentation for formatting the from fields properly.
Note: The email address you use must be a valid created account in the cPanel.