Controller/ContactController.php
public function send()
    {
        $optInValue = \OxidEsales\Eshop\Core\Registry::getConfig()->getRequestParameter('c_oegdproptin');
        if ($this->isOptInValidationRequired() && !$optInValue) {
            \OxidEsales\Eshop\Core\Registry::get(\OxidEsales\Eshop\Core\UtilsView::class)->addErrorToDisplay('OEGDPROPTIN_CONTACT_FORM_ERROR_MESSAGE');
            $this->optInError = true;
            return false;
        }

        return parent::send();
    }
public function send()
    {
        $optInValue = \OxidEsales\Eshop\Core\Registry::getConfig()->getRequestParameter('c_oegdproptin');
        if ($this->isOptInValidationRequired() && !$optInValue) {
            \OxidEsales\Eshop\Core\Registry::get(\OxidEsales\Eshop\Core\UtilsView::class)->addErrorToDisplay('OEGDPROPTIN_CONTACT_FORM_ERROR_MESSAGE');
            $this->optInError = true;
            return false;
        }

        return parent::send();
    }
Validation and contacts email sending

@return bool