In order to protect your Drupal application from unwanted messages, you can use the Akismet module for Drupal. This module is based on the Automattic Kismet (Akismet) project, which is dedicated to fighting spam.

The module is installed as any other Drupal module. Once you enable Akismet, you can configure it from your Drupal admin area > Administer > Site Configuration > Akismet. In order to use Akismet, you should enter your WordPress.com API  Key in the corresponding field.