title: Why am I getting smtplib.SMTPAuthenticationError: (500, b'5.3.3 Unrecognized command') using code that worked a month ago?
body: <p>I used the following code successfully last month to connect to and send mail through an Exchange server. I am using python 3.5.</p>
  
  <pre><code>import smtplib
  # ...
  s=smtplib.SMTP('outlook.office365.com', 587)
  s.starttls()
  s.login(user, pwd)
  </code></pre>
  
  <p>Today, it gives me</p>
  
  <p><code>smtplib.SMTPAuthenticationError: (500, b'5.3.3 Unrecognized command')</code></p>
  
  <p>I see a related bug report <a href="https://bugs.python.org/issue25446" rel="nofollow">here</a> but cannot figure out how that helps me.</p>
  
  <p>What am I doing wrong?</p>