Código PHP:
$link = new PDO($dns,$user, $password);
$mail=$_POST['mail'];
$link->quote($mail);
$sql="SELECT idusers WHERE mail='".$mail."'";
$resulset=$link->query($sql);
if($resulset->rowCount()!=0){
echo 'Gracias por esperar.';
}else{
}
Call to a member function rowCount()
saludos