If you’re unable to send email usign a form, either via wordpress using any of their many plugins or via a php form page, it’s not wordpress or the script, most likely it’s your server configuration.
Make sure that sendmail for PHP is enabled (most likely it is since by default it should be). But check with your hosting provider to make sure it is.
Also make sure you have a root user email enabled for your server. This is most likely the problem. Whatever your root user user name is, make sure an email box has been created for it. A Virtmap or user box.