Issue #3148982 by Project Update Bot: Automated Drupal 9 compatibility fixes

sys.module

@@ -206,10 +206,10 @@ function sys_cron() {
       foreach ($emails_to as $email) {
         $result = $mailManager->mail($module, $key, trim($email), $langcode, $params, NULL, TRUE);
         if ($result['result'] !== TRUE) {
-          drupal_set_message(t('There was a problem sending your message and it was not sent.'), 'error');
+          \Drupal::messenger()->addError(t('There was a problem sending your message and it was not sent.'));
         }
         else {
-          drupal_set_message(t('Your message has been sent.'));
+          \Drupal::messenger()->addStatus(t('Your message has been sent.'));
         }
       }
       $state->set('sys_settings', date('d/m'));