You need to add line breaks to the first line of your headers too:
if( $_POST['email'] && !preg_match( "/[\r\n]/", $_POST['email']) ) {
$headers = "From: $_POST[email]\r\n";
} else {
$headers = "From: $youremail\r\n";
}
$headers .= "Bcc: yyy@yyy.com\r\n";
mail($youremail, 'Richiesta Informazioni dal Sito Web', $body, $headers );
}