Ciao
Prova cosi 
Codice PHP:
<?php
//elabora_form.php
function ControlloEmail($email) {
if (function_exists('filter_var')) {
return filter_var($email, FILTER_VALIDATE_EMAIL) !== FALSE;
} else {
return preg_match('/^(?:[\w\!\#\$\%\&\'\*\+\-\/\=\?\^\`\{\|\}\~]+\.)*[\w\!\#\$\%\&\'\*\+\-\/\=\?\^\`\{\|\}\~]+@(?:(?:(?:[a-zA-Z0-9_](?:[a-zA-Z0-9_\-](?!\.)){0,61}[a-zA-Z0-9_-]?\.)+[a-zA-Z0-9_](?:[a-zA-Z0-9_\-](?!$)){0,61}[a-zA-Z0-9_]?)|(?:\[(?:(?:[01]?\d{1,2}|2[0-4]\d|25[0-5])\.){3}(?:[01]?\d{1,2}|2[0-4]\d|25[0-5])\]))$/', $email);
}
}
$email = $_POST['email'];
$testo = $_POST['banner'];
if($email== null ){
echo"inserire un email";
}elseif($testo==null){
echo"inserire un testo";
}elseif(!ControlloEmail($email)){
echo"inserire un email valida";
}else{
mail('TuaEmail', 'Soggetto', $testo);
}
?>