title: Add attachments to existing eml file
body: <p>I have an existing eml file which contain among others body and attachments.</p>
  
  <p>I simply want to add attachments to this file, not erase existing onlt to add attachments.</p>
  
  <p>I have this code to create eml:</p>
  
  <pre><code>public static void createMessage(String to, String from, String subject, String body, List&lt;File&gt; attachments) {
  try {
      Message message = new MimeMessage(Session.getInstance(System.getProperties()));
      message.setFrom(new InternetAddress(from));
      message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(to));
      message.setSubject(subject);
      // create the message part 
      MimeBodyPart content = new MimeBodyPart();
      // fill message
      content.setText(body);
      Multipart multipart = new MimeMultipart();
      multipart.addBodyPart(content);
      // add attachments
      for(File file : attachments) {
          MimeBodyPart attachment = new MimeBodyPart();
          DataSource source = new FileDataSource(file);
          attachment.setDataHandler(new DataHandler(source));
          attachment.setFileName(file.getName());
          multipart.addBodyPart(attachment);
      }
      // integration
      message.setContent(multipart);
      // store file
      message.writeTo(new FileOutputStream(new File("c:/mail.eml")));
  } catch (MessagingException ex) {
      Logger.getLogger(Mailkit.class.getName()).log(Level.SEVERE, null, ex);
  } catch (IOException ex) {
      Logger.getLogger(Mailkit.class.getName()).log(Level.SEVERE, null, ex);
  }
  </code></pre>
  
  <p>}</p>
  
  <p>But how do i add to existing rather then create?</p>