Auto reply for Unknown recipient

1. Create new Google Group from your admin console.
2. Define the settings as shown below.

3. Select Access Settings.

4. Select Email options from the “Settings” menu.

5. And define your message in “Auto replies” and Save the changes.

7. Go to Dashboard – Apps – Google Apps – Gmail – Advanced Settings – Default Routing.

8. Select Add settings.

9. Define the settings mentioned in following image.

10. Done.