def _fetch_attachment_contents(self, content_dict, _mail_service):
        attachments = content_dict.get('attachments', []) if content_dict else []
        for attachment in attachments:
            retrieved_attachment = yield _mail_service.attachment(attachment['ident'])
            attachment['raw'] = retrieved_attachment['content']
        content_dict['attachments'] = attachments
        defer.returnValue(content_dict)