To route unknown g suite users to another email server for multiple reasons. One being cost saving of a mailbox. This diagram is a common workflow. 

1. Navigate to https://admin.google.com/ and login

2. Navigate to https://admin.google.com/u/1/ac/apps/gmail/hosts 

3. Click "ADD ROUTE"

4. Click this field.

5. Type "mx1.mailhop.org - unknown users"

6. Click this field.

7. Type "mx1.mailhop.org"

8. Click here.

9. Click this field.

10. Type "25"

11. Click "Test TLS connection"

12. Click "SAVE"

13. Navigate to https://admin.google.com/u/1/ac/apps/gmail/routing

14. Click "ADD ANOTHER RULE"

15. Click this field.

16. Type "Route unknown users"

17. Click inbound.

18. Click internal - receiving.

19. Click Change Route

20. Down Arrow on normal routing

21. Click "Unknown Users - DuoCircle"

22. Suppress Bounces

23. Click "SAVE"

This completes the split delivery setup for your domain name. 

Going forward if any email is sent, the email will be first routed to your Gsuite. If the account exists under Gsuite the mail will be delivered successfully.

In case the email account does not exist, the mail will be routed to your Business/ Enterprise Email server and the message will be delivered to the intended recipient.