Fatal error: Uncaught Error: Class "Drupal\Core\Form\ConfigFormBase" not found in /home/www/drupal8/test/modules/contrib/mimemail/src/Form/AdminForm.php:17
Stack trace:
#0 {main}
thrown in /home/www/drupal8/test/modules/contrib/mimemail/src/Form/AdminForm.php on line 17