moduleManager = $moduleManager; } /** * @param Observer $observer */ public function execute(Observer $observer) { if ($this->moduleManager->isEnabled('Magento_CustomerSampleData')) { $form = $observer->getForm(); $messages = $form->getElements()->searchById('messages'); /** @var Messages $messagesRender */ $messagesRender = $messages->getRenderer(); $messagesRender->addError( 'Email sending is disabled when the Magento_CustomerSampleData module is installed. Read more here .' ); } } }