title: OAuth2 authentication error using 'python-o365' library
body: <p>I have able to successfully connect and read emails using the '<a href="https://github.com/Narcolapser/python-o365" rel="nofollow noreferrer">python-o365</a>' library:</p>
  
  <pre><code>Connection.oauth2('Client_ID','Client_Secret',store_token=True)
  inbox = FluentInbox()
  for message in inbox.fetch_next(2):
     print(message.getSubject())
  </code></pre>
  
  <p>However, when I try to send an email using a more basic example, I am receiving a <code>401</code> response from the server.</p>
  
  <pre><code>Connection.oauth2('Client_ID','Client_Secret',store_token=True)
  att = Attachment(path=FilePath)
  m = Message()
  m.setRecipients(EmailTo)
  m.setSubject('DBM Errors Identified - ' + FileName)
  m.setBody(MessageBody)
  m.attachments.append(att)
  m.sendMessage()
  </code></pre>
  
  <p>I have also tried setting the connection object and passing it through as a parameter: </p>
  
  <pre><code>auth = Connection.oauth2('Client_ID','Client_Secret',store_token=True)
  m = Message(*auth=auth*)
  </code></pre>
  
  <p>That however results in an error message of:</p>
  
  <p><code>TypeError: 'Connection' object is not callable</code></p>
  
  <p>Thanks for the help!</p>