Php邮件功能随机工作，其他时间不起作用..可能出错？

Question

所以我正在使用PHP邮件功能发送邮件，它有时随机工作，有时则没有..可能出现什么问题？以下是我的代码

// send notification to enquiry owner
    $sql = 'SELECT `title`, `classified_poster_name`, `email` FROM `table_classified` WHERE `ad_id` = '.$clsID.' LIMIT 1';
    $result = mysql_query($sql); 
    if($row = mysql_fetch_array($result)) {
        $body =
            "You have received a new enquiry for classified '{$row['title']}' !\n\n"
            ."Sender name: {$sender_name}\n"
            ."Sender email: {$sender_email}\n"
            ."Message:\n{$sender_msg}\n\n"
            .'Sent: '.date('Y-m-d H:i')."\n";
        $body = nl2br($body);
        $fromAddress = "From: $sender_email\r\n" .
      "Reply-To: support@" . $_SERVER['SERVER_NAME'] . "\r\n" .
     "X-Mailer: PHP/" . phpversion();

     mail($row['email'], "New enquiry for classified '{$row['title']}' on $comp_name ", $body, $fromAddress);




    }