_getAttachmentsRaw(callback) {
    this.getRawEmail(parsedEmail => {
      const attachments = (parsedEmail || {}).attachments || [];
      callback(attachments.map(createAttachment));
    });
  }
Parses raw email to retrieve any encoded attachments (Only applies to raw payloads)
@private
@param {Function} callback Function which will receive an array, of attachments found, as the sole argument