An undefined variable is preventing me from continuing with my email form. What's missing?

?php 

if ($_SERVER["REQUEST_METHOD"] == "POST") {
  $name = trim(filter_input(INPUT_POST,"name",FILTER_SANITIZE_STRING));
  $email = trim(filter_input(INPUT_POST,"email",FILTER_SANITIZE_EMAIL));
  $details = trim(filter_input(INPUT_POST,"details",FILTER_SANITIZE_SPECIAL_CHARS));

if ($name == "" || $email == "" || $details == "" ) {
  echo "Please fill in the required fields: Name, E-Mail, and Message";
  exit;
}
if ($_POST["address"] != "") {
  echo "Bad form input";
  exit;
}

require("inc/phpmailer/class.phpmailer.php");

  $email_body = "";
  $email_body .= "Name " . $name . "\n";
  $email_body .= "E-Mail " . $email . "\n";
  $email_body .= "Message " . $details . "\n";

  $mail->setFrom($email, $name);
  $mail->addAddress('treehouse@localhost', 'Alejandro');     // Add a recipient

  $mail->isHTML(false);                                  // Set email format to HTML

  $mail->Subject = 'Personal Media Library Selection from ' . $name;
  $mail->Body    = $email_body;

  if(!$mail->send()) {
    echo 'Message could not be sent.';
    echo 'Mailer Error: ' . $mail->ErrorInfo;
    exit;
}

header("location:suggest.php?status=thanks");

}

$pageTitle = "Suggest a Media Item";
$section = "suggest";

include("inc/header.php"); ?>

<div class="section page">
    <h1>Suggest a Media Item</h1>
  <?php if (isset($_GET["status"]) && $_GET["status"] == "thanks") {
      echo "<p>Thanks for the e-mail! I&rsquo;ll check out your suggestion shortly.</p>";

  } else {
  ?>
    <form method="post" action="suggest.php">
    <table>
      <tr>
        <th><label for="name">Name</label></th>
        <td><input type="text" id="name" name="name"/></td>
      </tr>
      <tr>
        <th><label for="email">E-Mail</label></th>
        <td><input type="text" id="email" name="email"/></td>
      </tr>
      <tr>
        <th><label for="name">Suggest Item Details</label></th>
        <td><textarea name="details" id="details"></textarea></td>
      </tr>
      <tr style="display: none;">
        <th><label for="address">Address</label></th>
        <td><textarea name="address" id="address"></textarea>
        <p>Please leave this field blank</p></td>
      </tr>
    </table>
    <input type="submit" value="send"/>
    </form>
  <?php } ?>
</div>

<?php include("inc/footer.php"); ?>