电子邮件不发送它重定向到页面未请求的网页

Question

我只是在学习并且正在尝试将邮件表单从sql更改为PDO。 提交邮件时，将返回“页面未请求的常规错误”网页。 任何人都可以看到我做错了什么并帮助我排序吗？ 这是代码，表单首先成功提交到数据库。

<?php 
//mail and inert section start here====================================
if (isset($_POST['submit'])) {

// These set initial variables.
//$sendto is echoed checkbox, name="sendto[]"
$sendto = $_POST['sendto'];
$username = $_POST['username'];
$return_email = $_POST['email'];
$subject = $_POST['subject'];
$message = $_POST['message'];
//$errorurl = "../pages/Errorurl_contact.php";
 if($sendto=='') {


       echo"<div id ='message'><p style='padding: .5em; border: 2px solid red;'>You must pick a member to email, please click on the back button and check one of the member boxes&nbsp;&nbsp;<a href='../admin/users.php'><input type='button' value = 'Back'></a></p></div>";

 }

   //  set variables  before setting them programatically.
 if($username==''){


       echo"<div id ='message'><p style='padding: .5em; border: 2px solid red;'>Username is required, please click on the back button and fill in your username&nbsp;&nbsp;<a href='../admin/users.php'><input type='button' value = 'Back'></a></p></div>";

 }
   if (strlen($_POST['username']) >12) {

       echo"<div id ='message'><p style='padding: .5em; border: 2px solid red;'>Username has to be less than 12 characters, please click on the back button and try again&nbsp;&nbsp;<a href='../admin/users.php'><input type='button' value = 'Back'></a></p></div>";

   }

   if (!filter_var($return_email, FILTER_VALIDATE_EMAIL))
{   
    echo "<div id ='message'><p style='padding: .5em; border: 2px solid red;'>Invalid email address, please click the back button and re enter your email&nbsp;&nbsp;<a href='../admin/users.php'><input type='button' value = 'Back'></a></p></div>";

}
 if($subject==''){

       echo "<div id ='message'><p style='padding: .5em; border: 2px solid red;'>A subject is required, please click the back button and fill in a subject for your message&nbsp;&nbsp;<a href='../admin/users.php'><input type='button' value = 'Back'></a></p></div>";

 }
    if (isset($subject)) {
   $subject = trim($subject);
   $subject = strip_tags($subject);
   }
   if (strlen($_POST['subject']) >60) {

       echo"<div id = 'message'><p style='padding: .5em; border: 2px solid red;'>Subject has to be less than 60 characters&nbsp;&nbsp;<a href='../admin/users.php'><input type='button' value = 'Back'></a></P></div>";

   }
   else {
     if (isset($message)) {
   $message = trim($message);
   $message = strip_tags($message);
   }
//Check appropriate checkboxes are echoeing correct value====ERROR CHECKING===

//if(isset($_POST['sendto']))
 //      {
 //        foreach ($_POST['sendto'] as $value)
  //     {
  //       echo "sendto #{$value} was selected!\n";
  //     }
 //}
//insert to database section==============================================   
$mode="mysqli";
   if($mode == "mysqli") {

if(isset($_POST['sendto']) && is_array($_POST["sendto"])){
    $sendto = join('; ', $sendto);  
// sql query for INSERT form submission INTO
try {
/* Prepared statement, bind and execute */ 
                $stmt = $db->prepare("INSERT INTO mail (mailto,username,return_email,subject,message) VALUES (:sendto, :username,:return_email,:subject,:message)");


    //bind parameters           
   $stmt->bindValue(':sendto', $sendto, PDO::PARAM_STR);
   $stmt->bindParam(':username', $_POST['username'],PDO::PARAM_STR, 12);
   $stmt->bindParam(':return_email', $_POST['email']);
   $stmt->bindParam(':subject', $_POST['subject'], PDO::PARAM_STR, 60);
   $stmt->bindParam(':message', $_POST['message'], PDO::PARAM_STR);

    //protect against attacks       
                $username = htmlentities($username, ENT_QUOTES);
                $return_email = htmlentities($return_email, ENT_QUOTES);
                $subject = htmlentities($subject, ENT_QUOTES);
                $message = htmlentities($message, ENT_QUOTES);
                $stmt->execute();
}

             catch (PDOException $e) 
            {
                echo $e->getMessage();
            }
            echo "<p>Data submitted successfully</p>";

}
   }
   $mode = 'email';
  if ($mode == "email"){    
   if(isset($_POST['sendto'])) {

//email variables

// email send to recipients  
        $email_to = "xxx@example.com";
        $forward_to = implode(", ", $_POST['sendto']);
        $to = "$email_to; $forward_to";// required

        $email = $_POST['email']; // required         
        $username = $_POST['username']; // required     
        $subject = $_POST['subject']; // required
        $message = $_POST['message'];
        $from = $_POST['email'];
        $headers = "From:" . $from;
mail($to, $email, $username, $subject, $message, $headers);
echo "Mail Sent.";



//testing variables present
    #var_dump($username);
     #var_dump($subject);
      #var_dump($_POST['email']);
        #var_dump($to);
         #var_dump($email_message);
          #var_dump($email_from);
          //all good

    }
   }
  }
}