Some servers do not handle modern PHP code well.
If you get an error message something like Warning: getmxrr() is not supported
this means that the DNS look-up email validation function will not work. You can remove the
offending code from feedback1.php so that the page now looks like this:
Other possible errors may arise if your server does not have 'Register globals' switched on.
You may be able to switch these on by sending an .htaccess file
(how to make) up to your root directory,
which contains the following line of text: php_flag register_globals on