A good starting point for your PHP form is this article: http://64.13.255.16/articles/bulletproof_contact_form_with_php/
To get this form to work with our hosting properly you will need to set the "From" address in the code as below:
Where the code says:
mail($to,$subject,$message,$headers);
You need to add the from address in this format:
mail($to,$subject,$message,$headers,"-f your@email.here");
The address should be one thats activated on your server.
PHP safe mode will also need to be turned off in your plesk control panel.