<?php
$names = Array(
    "name"         => "Имя",
    "email"        => "Емаил",
    "phone"        => "Телефон",
    "product_name" => "Продукт",
);
foreach ($_POST as $key => $value) {
    if (array_key_exists($key, $names)) {
        $n = $names[$key];
        $text .= "$n : $value \n";
    }
}

$to      = "mail@mail.ru";
$headers = "Content-type: text/plain; charset = utf-8";
$subject = "письмо";
$send    = mail($to, $subject, $text, $headers);

if ($send) {
    echo "success";
}