php - html/phpコメントボックスがメールを送信しない

Question

phpファイルにリクエストを送信する単純なhtmlフォームがあり、phpファイルはメールを送信する必要があります。phpファイルへのリクエストは機能し、確認テキストが表示されますが、電子メールは送信されません。

私は本当に立ち往生していて、なぜ電子メールが送信されないのか理解できません。私のPHPに問題はありますか？

HTML

<form name="htmlform" method="post" action="html_form_send.php">
    <table width="450px">
     </tr>
     <tr>
     <td valign="top">
         <label for="first_name">First Name *</label>
     </td>
     <td valign="top">
       <input  type="text" name="first_name" maxlength="50" size="30">
     </td>
        </tr>

       <tr>
       <td valign="top">
           <label for="last_name">Last Name *</label>
       </td>
       <td valign="top">
          <input  type="text" name="last_name" maxlength="50" size="30">
       </td>
       </tr>
        <tr>
        <td valign="top">
             <label for="email">Email Address *</label>
        </td>
        <td valign="top">
              <input  type="text" name="email" maxlength="80" size="30">
        </td>

         </tr>
         <tr>
         <td valign="top">
             <label for="telephone">Estimated Quantity</label>
         </td>
          <td valign="top">
                <input  type="text" name="telephone" maxlength="30" size="30">
          </td>
          </tr>
         <tr>
          <td valign="top">
                <label for="comments">Product wanted for import *</label>
          </td>
          <td valign="top">
               <textarea  name="comments" maxlength="1000" cols="25" rows="6">  
           </textarea>
          </td>

          </tr>
           <tr>
           <td colspan="2" style="text-align:center">
               <input type="submit" value="Submit"> 
           </td>
           </tr>
    </table>
 </form>

PHP

<?php
if(isset($_POST['email'])) {

    $email_to = "jplustradingltd@gmail.com";

    $email_subject = "J Plus Trading Website Query";


    function died($error) {
        // your error code can go here
        echo "We are very sorry, but there were error(s) found with the form you submitted. ";
        echo "These errors appear below.<br /><br />";
        echo $error."<br /><br />";
        echo "Please go back and fix these errors.<br /><br />";
        die();
    }

    // validation expected data exists
    if(!isset($_POST['first_name']) ||
        !isset($_POST['last_name']) ||
        !isset($_POST['email']) ||
        !isset($_POST['telephone']) ||
        !isset($_POST['comments'])) {
        died('We are sorry, but there appears to be a problem with the form you submitted.');       
    }

    $first_name = $_POST['first_name']; // required
    $last_name = $_POST['last_name']; // required
    $email_from = $_POST['email']; // required
    $telephone = $_POST['telephone']; // not required
    $comments = $_POST['comments']; // required

    $error_message = "";
    $email_exp = '/^[A-Za-z0-9._%-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}$/';
  if(!preg_match($email_exp,$email_from)) {
    $error_message .= 'The Email Address you entered does not appear to be valid.<br />';
  }
    $string_exp = "/^[A-Za-z .'-]+$/";
  if(!preg_match($string_exp,$first_name)) {
    $error_message .= 'The First Name you entered does not appear to be valid.<br />';
  }
  if(!preg_match($string_exp,$last_name)) {
    $error_message .= 'The Last Name you entered does not appear to be valid.<br />';
  }
  if(strlen($comments) < 2) {
    $error_message .= 'The Comments you entered do not appear to be valid.<br />';
  }
  if(strlen($error_message) > 0) {
    died($error_message);
  }
    $email_message = "Form details below.\n\n";

    function clean_string($string) {
      $bad = array("content-type","bcc:","to:","cc:","href");
      return str_replace($bad,"",$string);
    }

    $email_message .= "First Name: ".clean_string($first_name)."\n";
    $email_message .= "Last Name: ".clean_string($last_name)."\n";
    $email_message .= "Email: ".clean_string($email_from)."\n";
    $email_message .= "Telephone: ".clean_string($telephone)."\n";
    $email_message .= "Comments: ".clean_string($comments)."\n";


// create email headers
$headers = 'From: '.$email_from."\r\n".
'Reply-To: '.$email_from."\r\n" .
'X-Mailer: PHP/' . phpversion();
@mail($email_to, $email_subject, $email_message, $headers);  
?>

<!-- place your own success html below -->

Thank you for contacting us. We will be in touch with you very soon.

<?php
}
die();
?>