No recipients have been added when trying to send message with Flask-Mail
Question: I am trying to send email with Flask-Mail. I create the message with
recipients, but I get `AssertionError: No recipients have been added` when I
try to send it. In the following code, I print out the message recipients and
they are correct. How do I fix this error?

    
    
    from flask import Flask
    from flask_mail import Message, Mail
    
    app = Flask(__name__)
    app.config.update(
        DEBUG=True,
        MAIL_SERVER='smtp.gmail.com',
        MAIL_PORT=465,
        MAIL_USE_SSL=True,
        MAIL_USERNAME='socialcreditsystem@gmail.com',
        MAIL_PASSWORD='mypassword'
    )
    mail = Mail(app)
    
    @app.route('/')
    def hello_world():
        msg=Message('hey hey hey', sender='socialcreditsystem@gmail.com', recipients=['julian.fink1000@gmail.com'])
        print(msg.sender, msg.recipients)
        # ('socialcreditsystem@googlemail.com', ['julian.fink1000@googlemail.com'])
        print(msg.send_to)
        # set(['julian.fink1000@googlemail.com'])
        mail.send_message(msg)
        return 'Hello World!'
    
    if __name__ == '__main__':
        app.run()
    
    
    
    Traceback (most recent call last):
      File "C:\Python27\lib\site-packages\flask\app.py", line 1836, in __call__
        return self.wsgi_app(environ, start_response)
      File "C:\Python27\lib\site-packages\flask\app.py", line 1820, in wsgi_app
        response = self.make_response(self.handle_exception(e))
      File "C:\Python27\lib\site-packages\flask\app.py", line 1403, in handle_exception
        reraise(exc_type, exc_value, tb)
      File "C:\Python27\lib\site-packages\flask\app.py", line 1817, in wsgi_app
        response = self.full_dispatch_request()
      File "C:\Python27\lib\site-packages\flask\app.py", line 1477, in full_dispatch_request
        rv = self.handle_user_exception(e)
      File "C:\Python27\lib\site-packages\flask\app.py", line 1381, in handle_user_exception
        reraise(exc_type, exc_value, tb)
      File "C:\Python27\lib\site-packages\flask\app.py", line 1475, in full_dispatch_request
        rv = self.dispatch_request()
      File "C:\Python27\lib\site-packages\flask\app.py", line 1461, in dispatch_request
        return self.view_functions[rule.endpoint](**req.view_args)
      File "C:\Users\Julian\PycharmProjects\flask_mail_test\flask_mail_test.py", line 26, in hello_world
        mail.send_message(msg)
      File "C:\Python27\lib\site-packages\flask_mail.py", line 503, in send_message
        self.send(Message(*args, **kwargs))
      File "C:\Python27\lib\site-packages\flask_mail.py", line 493, in send
        message.send(connection)
      File "C:\Python27\lib\site-packages\flask_mail.py", line 428, in send
        connection.send(self)
      File "C:\Python27\lib\site-packages\flask_mail.py", line 176, in send
        assert message.send_to, "No recipients have been added"
    AssertionError: No recipients have been added
    


Answer: You're using the wrong function. `mail.send_message` is a shortcut to build
and send a message, it takes the same args as `Message`. Use `mail.send(msg)`
to send an existing `Message` instance.

