php验证邮箱

<?php
if(isset($_POST['email'])){
    $email = $_POST['email'];
    if(filter_var($email, FILTER_VALIDATE_EMAIL)){
        echo '<p>This is a valid email.<p>';
    }else{
        echo '<p>This is an invalid email.</p>';
    }
}
?>
<form action="" method="post">
    Email: <input type="text" name="email" value=" <?php echo $_POST['email']; ?> ">
    <input type="submit" value="Check Email">
</form>