How to Set up Google Workspace Email Routing using Split Delivery

Introduction

During a corporate migration to Google Workspace, or when integrating a specialized legacy email server with your primary domain, you may need to route emails to two different platforms simultaneously. This is achieved through Split Delivery. Split Delivery ensures that users on the legacy system and users on Google Workspace share the same domain name (e.g., @company.com) without losing messages. This guide explains how to configure Split Delivery in the Google Admin Console.

Prerequisites

You must have Super Administrator access to Google Workspace. The MX records for your primary domain must be pointed to Google (so Google receives the mail first). You also need the hostname or IP address of your secondary/legacy email server.

Step 1: Add the Secondary Server as a Host

Before creating the routing rule, you must define the destination server.

1. Log in to the Google Admin console.
2. Navigate to Apps > Google Workspace > Gmail > Hosts.
3. Click Add route. Give it a descriptive name (e.g., “Legacy Exchange Server”).
4. Choose Single host and enter the IP address or hostname of the secondary server. Set the port (usually 25 or 587).
5. Check the box for Require secure transport (TLS) to encrypt transit. Click Save.

Step 2: Configure the Routing Rule

Now, you instruct Gmail on how to handle incoming messages for unknown users.

1. Navigate to Apps > Google Workspace > Gmail > Routing.
2. Scroll down to the Routing section and click Add Rule.
3. Name the rule (e.g., “Split Delivery to Legacy Server”).

Step 3: Define the Email Messages to Affect

Under Messages to affect, check the boxes for Inbound and Internal – receiving. This ensures both external emails and internal emails originating from Workspace users are evaluated by the rule.

Step 4: Set the Route Destination

Scroll down to Step 3: For the above types of messages, do the following.

• Under Route, check the box for Change route.
• Select the host you created in Step 1 (“Legacy Exchange Server”) from the dropdown menu.

Step 5: Apply Account Types (The Split Condition)

The most critical step is ensuring Google only forwards emails for users who do not exist in Workspace.

• Scroll down to Show options at the bottom of the rule window.
• Under Account types to affect, ensure Unrecognized / Catch-all is the only option selected. Do not select Users or Groups.

Click Save to activate the rule.

How it Works

When an email arrives for [email protected] (who has migrated to Google), Google recognizes the account and delivers it to their Gmail inbox. When an email arrives for [email protected] (who is still on the legacy server), Google does not recognize the account. Instead of bouncing the email with an NDR, the Split Delivery rule triggers and forwards the message to the legacy host defined in Step 1.