Filter_validate_email无法在实时服务器上运行，但在localhost

Question

我使用php的FILTER_VALIDATE_EMAIL来检查电子邮件的格式是否正确。 当我还在我的本地机器上运行xampp时它工作正常（php 5.5）。 将其上传到实时服务器后，我一直收到电子邮件无效＆＃34;消息电子邮件是否正确（已检查过php 5.3,5.5和5.6）。

以下是代码：

<?php 
     //Variables used for registering
        $username = mysql_real_escape_string($_POST['username']);   
        $email = mysql_real_escape_string($_POST['email']);
        $password = mysql_real_escape_string($_POST['password']);
        $submit = $_POST['register'];
        $joindate = date("y.m.d");
        //Get data from database to check if a user exists

        $userssql = mysql_query("SELECT * FROM users WHERE username = '$username'");

        if(isset($submit)) {
            if(mysql_num_rows($userssql) == 0) {
                if(filter_var($email, FILTER_VALIDATE_EMAIL)) {
                    $encryptpass = password_hash($password, PASSWORD_DEFAULT);
                    $register = mysqli_query("INSERT INTO users(username, email, password, joindate) VALUES('$username', '$email', '$encryptpass', '$joindate')");
                    header("location: login.php");
                }
                else {
                 ?>
                 <script type="text/javascript">
                  $('#email-error').text("Invalid email");
                 </script>
                            <?php
                }
            }
            else {
                ?>
                <script type="text/javascript">
                    $('#username-error').text("Username already exists");
                </script>
                <?php 
            }     
        }
    ?>

任何想法可能出错？