Extending Django Organizations backends. Use mixin custom functionality to override default backends using your own application. This example takes an optional `connection` argument and passes it to `send_mail`.

custom_backends.py

from organizations.backends.defaults import RegistrationBackend, InvitationBackend


class SendMailMixin(object):
  
      def _send_email(self, user, subject_template, body_template,
            sender=None, connection=None, **kwargs):
        """Utility method for sending emails to new users"""
        if sender:
            from_email = "%s %s <%s>" % (sender.first_name, sender.last_name,
                    settings.DEFAULT_FROM_EMAIL)
            reply_to = "%s %s <%s>" % (sender.first_name, sender.last_name,
                    sender.email)
        else:
            from_email = settings.DEFAULT_FROM_EMAIL
            reply_to = from_email

        headers = {'Reply-To': reply_to}
        kwargs.update({'sender': sender, 'user': user})
        ctx = Context(kwargs, autoescape=False)

        subject_template = loader.get_template(subject_template)
        body_template = loader.get_template(body_template)
        subject = subject_template.render(ctx).strip() # Remove stray newline characters
        body = body_template.render(ctx)
        return EmailMessage(subject, body, from_email, [user.email],
                headers=headers, connection=connection).send()
                

class MyRegistrationBackend(SendMailMixin, RegistrationBackend):
  pass


class MyInvitationBackend(SendMailMixin, InvitationBackend):
  pass

settings.py

INVITATION_BACKEND = 'myapp.backends.MyInvitationBackend'
REGISTRATION_BACKEND = 'myapp.backends.MyRegistrationBackend'