邮件在刷新时再次发送（PHP邮件功能）

Question

重复的问题，对我来说没有合适的答案...... 我已经看到围绕这个主题的一些威胁，但它们都没有帮助解决我的问题。问题是标题所说的。我有一个邮件脚本，工作正常，但我的脚本继续刷新时再次发送表单的输入。我该如何解决这个问题？

PS：我使用header('Location: http://www.intu.nl/versie2/contact'); 这是我的代码：

        <?php
    //if "submitted" variable is filled out, send email
      if (isset($_REQUEST['submitted']))  {
        $errors = array();
        $ontvanger = "my@email.com";

        //emailchek
        if (!empty($_REQUEST['email'])) {
          $afzender = $_REQUEST['email'];
          if (!filter_var($afzender, FILTER_VALIDATE_EMAIL) === false) {
            $afzender = $_REQUEST['email'];
          }
          else {
            $errors[] = "Uw E-mail adres niet juist is ingevuld.";
          }
        } else {
          $errors[] = 'Uw E-Mail adres niet is ingevuld.';
        }
        // Naam check
        if (!empty($_REQUEST['name'])) {
          $naam = $_REQUEST['name'];
        } else {
          $naam = 'is niet ingevuld.';
        }
        //nummer check
        if (!empty($_REQUEST['phone'])) {
          $telefoon = $_REQUEST['phone'];
          if(!ctype_digit($telefoon)){
            $telefoon = "geen telefoonnummer meegegeven";
          }
        } else {
          $telefoon = "geen telefoon nummer meegegeven";
        }
        if (!empty($_REQUEST['comment'])) {
          $inhoud = $_REQUEST['comment'];
        } else {
          $errors[ ] = "Uw bericht was leeg";
        }

        $headers = array();
        $headers[ ] = "MIME-Version: 1.0";
        $headers[ ] = "Content-type: text/plain; charset=utf-8";
        $headers[ ] = "Email: " . $afzender;
        $headers[ ] = "Telefoon nummer: " . $telefoon;
        $headers[ ] = "naam: " . $naam;
        $headers[ ] = "Inhoud van het bericht:";

        //send email
        if (empty($errors)) {
          mail($ontvanger, "Een E-Mail verzonden van INTUhome.nl", $inhoud, implode("\r\n", $headers), "-f".$afzender);
          print('<h2 class="green"><i class="icon-ok"></i>Bedankt voor uw bericht! </h2><h3> Wij zullen zo snel mogelijk contact met u opnemen.</h3>');
          header('Location: http://www.intu.nl/versie2/contact');
        }
        else {
          echo "<h2 class='green'>De E-Mail is niet verzonden omdat:</h2>";
          foreach ($errors as $msg) {
            echo '<li><h3>' . $msg . '</h3></li>';
          }
          echo '</br>';
          echo '<A HREF="../contact"><h4>Ga terug</h4></A>';
        }
      } else{
    ?>
    <form method="get">
      <div class="input-group input-group-lg"><span class="input-group-addon"><span class="glyphicon glyphicon-user"></span></span>
        <input name="name" type="text" placeholder="Naam" class="form-control">
      </div>
      <div class="input-group input-group-lg"><span class="input-group-addon"><span class="glyphicon glyphicon-earphone"></span></span>
        <input name="phone" type="text" placeholder="Telefoon-nummer" class="form-control">
      </div>
      <div class="input-group input-group-lg"><span class="input-group-addon"><span class="glyphicon glyphicon-envelope"></span></span>
        <input name="email" type="text" placeholder="Email address" class="form-control">
      </div>
      <div class="input-group input-group-lg">
        <textarea rows="5" name="comment" class="form-control"></textarea>
      </div>
      <input name="submitted" type="submit" class="btn btn-default">
    </form>
    <?php
      }
     ?>