title: TTK progress bar blocked when sending email
body: <p>I am writing an app in python using tkinter. In this app I am trying to send out a batch of emails and I want to show a progress bar while they are being sent. I am able to create the progress bar and start it, but when the emails are being sent, the bar just stops moving (If it is started way before the emails are sent, I want to start the bar just before the emails are sent, but it just hangs and nothing moves on the bar when I do it like this.</p>
  
  <pre><code>startProgressBar()
  sendEmails()
  stopProgressBar()
  </code></pre>
  
  <p>I have tried putting the sending of emails into a separate thread, but I don't seem to be having any luck. I am using the high-level Threading module. Are there any suggestions on what to do? Perhaps I am not getting the threading part correct. I am using the smtplib to send emails.</p>