title: python3 use google app engine to receive email, than how to get date and size properly
body: <p>I used GAE-mail to receive email, in the email handle, I am able to received body, sender, subject etc from mail_message.</p>
  <pre><code>mail_message = mail.InboundEmailMessage(data)
  # supported attributes is=&gt;{
           'amp_html',
           'attachments',
           'bcc',
           'body',
           'cc',
           'headers',
           'html',
           'reply_to',
           'sender',
           'subject',
           'to'
          }
  </code></pre>
  <p>however, I want some additional attributes, email_size and sentdate, what is the best practice to get these two attributes?</p>
  <p>thanks in advance</p>