title: Django settings - dynamic value for DEFAULT_FROM_EMAIL
body: <p>I'd like to be able to change sender email address from the admin. However, the default sender email is specified in <code>settings.py</code> with <code>DEFAULT_FROM_EMAIL</code>. </p>
  
  <p>What's a good approach to achieving this?</p>
  
  <p>Edit:<br>
  The main problem here is that <code>DEFAULT_FROM_EMAIL</code> is used by third-party apps included in my project, and I'd like to avoid messing with their code, for obvious reasons...</p>