def _get_from_environ(self, key, default):
        """Access a value from os.environ. Handles proxed variables, e.g. SMTP_LOGIN={{MAILGUN_LOGIN}}.
        Returns a tuple (envvar_key, envvar_value, proxied_key). The ``envvar_key`` will be different from
        the passed key for proxied variables. proxied_key will be None if the envvar isn't proxied.
        """
        env_key = self._get_key(key)
        value = os.environ.get(env_key, default)
        if hasattr(value, "strip"):
            match = _PROXIED_PATTERN.match(value)
            if match:  # Proxied variable
                proxied_key = match.groups()[0]
                return key, self._get_from_environ(proxied_key, default)[1], proxied_key
        return env_key, value, None