there are a couple of problems:
1) the action of the form is to post to the /HDWForm2Mail/Form2Mail.php file.
All form processing must occur on the forms action page.
this means that the server validation behavior must be added to the /HDWForm2Mail/Form2Mail.php file.
open that file, go to the binding panel. Click the plus button, select Form Data, click the folder icon and select the form page.
now go to the server behaviors panel and add the Server Validation Server behavior.
2) You have a server validation behavior for each form element, you only need one server validation behavior that is configured to validate all of the form elements.