title: Flask-Mail breaks Celery
body: <p>I've got a Flask app where celery works fine and Flask-Mail on its own works fine as well.</p>
  
  <pre><code>from celery import Celery
  from flask_mail import Mail, Message
  app = Flask(__name__)
  mail = Mail(app)
  
  celery = Celery('main_app', 
                   broker='mongodb://localhost',
                   backend='mongodb://localhost')
  @celery.task
  def cel_test():
       return 'cel_test'
  
  @app.route('/works_maybe')
  def works_maybe():
      return cel_test.delay()
  </code></pre>
  
  <h1>SO FAR, SO GOOD</h1>
  
  <p>cel_test works fine with the celery worker; everything shows up in mongo.</p>
  
  <p>But here's where it gets weird. The "signup" plus mail method works 100% without <code>@celery.task</code>, but blows up when it becomes a task.</p>
  
  <pre><code>@celery.task
  def send_email(some_arg, name, email):
      msg = Message(…message details..)
      return mail.send(msg)
  
  @app.route("/signup", methods=['POST'])
  def signup():
      return send_email.delay(...stuff for the message…)
  </code></pre>
  
  <h1>THE TRACE</h1>
  
  <pre><code>R = retval = fun(*args, **kwargs)
  File "/Users/username/pymods/virtualenvs/directory/lib/python2.7/site-packages/celery-3.0.15-py2.7.egg/celery/task/trace.py", line 415, in __protected_call__
  return self.run(*args, **kwargs)
  File "/Users/username/pymods/directory/directory/main_app/main_app.py", line 43, in send_email
  something = 'a string in the Message'),
  File "/Users/username/pymods/virtualenvs/directory/lib/python2.7/site-packages/flask/templating.py", line 123, in render_template
  ctx.app.update_template_context(context)  
  AttributeError: 'NoneType' object has no attribute 'app'
  </code></pre>
  
  <p>Could someone explain why in one case celery works great but when I involve mail.send(msg) it breaks?</p>
  
  <p>Perhaps there is something I need to learn with python more generally?</p>
  
  <p>Any thoughts, if at least as to approach to this type of issue would be greatly appreciated.</p>