public function getMessageRules()
    {
        $rules = [];
        $rules = array_merge($rules, $this->getMutualRules());
        if (is_string($this->attachmentAttribute) && !empty($this->attachmentAttribute)) {
            $rules[] = [$this->attachmentAttribute, 'safe'];
        }
        if (is_string($this->receivedAtAttribute) && !empty($this->receivedAtAttribute)) {
            $rules[] = [$this->receivedAtAttribute, 'safe'];
        }
        if (is_string($this->readAtAttribute) && !empty($this->readAtAttribute)) {
            $rules[] = [$this->readAtAttribute, 'safe'];
        }
        return $rules;
    }