def METHOD_NAME(self, fixture_path: str) -> EmailMessage:
    if not self._does_fixture_path_exist(fixture_path):
        raise CommandError(f"Fixture {fixture_path} does not exist")
    if fixture_path.endswith(".json"):
        return self._parse_email_json_fixture(fixture_path)
    else:
        with open(fixture_path, "rb") as fp:
            message = email.message_from_binary_file(fp, policy=email.policy.default)
            # https://github.com/python/typeshed/issues/2417
            assert isinstance(message, EmailMessage)
            return message