Почему не приходит сообщение на почту? PHP

`<?php
$name = $_POST['name'];
$face = $_POST['face'];
$personal_account = $_POST['personal_account'];
$addres = $_POST['addres'];
$email = $_POST['email'];
$phone = $_POST['phone'];
$text = $_POST['text'];

$name = htmlspecialchars($name);
$face = htmlspecialchars($face);
$personal_account = htmlspecialchars($personal_account);
$addres = htmlspecialchars($addres);
$email = htmlspecialchars($email);
$phone = htmlspecialchars($phone);
$text = htmlspecialchars($text);

$name = urldecode($name);
$face = urldecode($face);
$personal_account = urldecode($personal_account);
$addres = urldecode($addres);
$email = urldecode($email);
$phone = urldecode($phone);
$text = urldecode($text);

mail("official_deh9@mail.ru","Заявка с сайта", "Имя: " . "$name" . "\n" . "Телефон: " . "$phone" . "\n" . "E-mail: " . "$email" . "\n\n" . "Сообщение: " . "\n" . "$mess");
if (mail == TRUE) {
echo "Заявка отправлена.";
} else {
echo "Ошибка отправки.";
}
?>`