How to set up Email Rerouting (Split Delivery)?

How to set up Email Rerouting (Split Delivery)?

Google Workspace can be configured with split delivery to support a hybrid architecture where users share the same domain across two different email systems.
In this setup, Google Workspace acts as the primary "gatekeeper" for all incoming mail, delivering messages to its own Google Workspace users and forwarding the remaining Non Google Workspace users' mail to your on-premise server.
Example:
Your domain: abc.com
You have total 5 user/email accounts under this domain hosted with your existing email server/providers.
You want to setup 2 user account for Google Workspace.
So, you first point the MX record of abc.com to SMTP.GOOGLE.COM and setup a email routing in Google Workspace to forward/process the incoming email of non-Google Workspace user to your existing email server.

How the Mail Flows Now

  1. Email for Google User: Internet → Google → Delivered to Gmail inbox.

  2. Email for Non-Google User: Internet → Google → User not found → Route to Legacy Server → Delivered to Legacy inbox.


Before you start:

To implement this hybrid environment, the following conditions must be met:
  • Primary MX Records: Your domain's MX records must point to Google.
  • Recipient Location: Users should have a mailbox in either Gmail or the on-premise system, but typically not both, to avoid confusion.
  • Host Setup: You must define your on-premise mail server as a "Host" within the Google Admin Console using its IP address or hostname.

Step 1: Add your Existing Server as a "Host"

First, you must tell Google where your legacy server is located.

  1. Log in to the Google Admin Console.

  2. Go to Menu > Apps > Google Workspace > Gmail > Hosts.

  3. Click Add Route.

  4. Name: Enter a name (e.g., "Legacy Email Server").

  5. Specify Email Server: Choose Single Host and enter your server's IP address or Hostname.

  6. Port: Use 25 (Standard) or 587.

  7. Security: Check Require CA signed certificate and Validate certificate hostname (recommended for security).

  8. Click Test TLS Connection to ensure Google can talk to your server, then click Save.

Step 2: Create the Split Delivery Routing Rule

Now, create the rule that pushes "unknown" mail to that host.

  1. Navigate back to Gmail Settings and click on Routing.

  2. Scroll down to the Routing section and click Configure (or Add Another Rule).

  3. Name: Enter "Split Delivery to Legacy".

  4. Email messages to affect: Check Inbound and Internal - receiving.

  5. For the above types of messages:

  • Change the dropdown to Modify message.

  • Check the box Change route.

  • Select the host you created in Step 1 (e.g., "Legacy Email Server").

  1. Options (The Most Important Part):

  • Scroll to the bottom and click Show options.

  • Under Account types to affect, UNCHECK "Users" and "Groups".

  • CHECK only Unrecognized / Catch-all.

  • This tells Google: "If you don't recognize the user (the 2 Google users), send the mail to the legacy server instead."

  1. Click Save.

Step 3: Update your DNS (MX Records)

For this to take effect, the world needs to send mail to Google first.

  1. Log in to your domain registrar (GoDaddy, Namecheap, etc.).

  2. Remove your existing MX records.

  3. Add Google’s MX records (Priority 1: SMTP.GOOGLE.COM).

  4. Wait for propagation: This can take 1–24 hours, though usually happens in minutes.

Important: Outgoing Mail (SPF Record)

To ensure your legacy server users can still send emails without being marked as spam, you must update your SPF record to include both servers.




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