How to restrict outgoing emails to external addresses

Problem

You want to restrict outgoing emails from users to external addresses.

Environment

You can set up a routing rule to reject outgoing emails from your domain to external addresses by following these steps:
  1. In your Admin console, go to Apps > Google Workspace > Gmail > Routing.
  2. Click Configure.
  3. Add a description for your rule.
  4. Under Email messages to affect, check the box for Outbound.
  5. Under For the above types of messages, select Reject message.
  6. (Optional) Add a custom rejection message.
  7. Click Show options.
  8. Check the box for Use address lists to bypass or control application of this setting.
  9. Select Apply address lists to correspondents.
  10. Select Bypass this setting for specific addresses / domains.
  11. Click Create or Edit list.
  12. Add a name for the address list.
  13. Click Add.
  14. Enter your domain name.
  15. Click Save.
  16. Back on the routing rule screen, click Save.

Solution

Creating a custom routing rule to reject outbound messages and only allowing emails sent within the domain.

Cause

Default setting will allow outbound emails to all domains.