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How To Configure Email Coexistence between Office 365 & Google Workspace

Email services are essential for any organization, regardless of its industry or size. Providers such as Microsoft, Google, Zoho, and others continuously update their offerings to meet customer needs. Sometimes, you may find that your company’s requirements are best met by using a combination of services from different providers. In such cases, setting up a split delivery service is the optimal solution.

What is “Split Delivery”?

Split delivery, as the term implies, involves distributing email services across multiple providers for a single domain or its subdomains. In simpler terms, it’s about configuring a service to host multiple destinations within itself and directing emails to various services as needed. For instance, imagine your organization primarily uses Microsoft 365 for email services. If you decide to introduce Google Workspace or another platform for a select group of users while maintaining Microsoft 365 for current users—without creating new accounts in Microsoft for the newcomers—”Split Delivery” is the strategy you would use.

How Does Split Delivery Work?

When an email is sent to your organization, it first consults the DNS panel to find the appropriate server via an MX lookup. The server then determines the email’s final destination. Suppose your organization has 50 users on Microsoft 365 and 20 on Google Workspace, with the DNS panel’s MX record pointing to Microsoft 365. Emails addressed to Microsoft 365 will go straight to its server. If the recipient doesn’t have an account on Microsoft 365, the email would normally bounce back. To prevent this, you instruct Microsoft’s Exchange server to redirect emails for non-existent users to another server (like Google Workspace) via connectors. This secondary server then delivers the email to the intended mailbox, if it exists.

Prerequisites for Setup

  • Ensure the DNS panel correctly incorporates Microsoft 365 records.
  • Combine the secondary service provider’s SPF records with those of Microsoft 365.
  • Verify that the intended users do not have existing accounts, aliases, Microsoft 365 Groups, or Distribution lists under Microsoft 365. Their SMTP addresses should not be present in the Microsoft 365 Tenant.

Precautions for the Secondary Service Provider

  • Record the MX records of the secondary service provider.
  • Confirm that the secondary service provider supports TLS.
  • For setups involving an on-premises server, use an IP address compatible with TSL. Additionally, ensure your ISP can handle ports 465, 993, 995, 587, 25, and 143.

Steps to Configure Email Coexistence between Office 365 & Google Apps

Setting up split delivery allows emails to be efficiently distributed between Microsoft 365 and another email service, ensuring seamless communication across different platforms within your organization. Here’s a step-by-step guide to configuring split delivery:

Step 1: Modify Your Domain Settings in Microsoft 365

1. Access the Microsoft Admin Portal: Log in at and navigate to Exchange in the left panel.

2. Adjust Accepted Domains: In the Exchange Admin Center, click on “Mail Flow” then “Accepted Domains.” Double-click your primary domain name in the list.

3. Set Domain to Internal Relay: In the pop-up window, change your domain status to ‘Internal Relay’. This ensures emails are delivered to recipients in your organization or relayed elsewhere as needed.

4. Subdomain Setup (Optional): If you have a subdomain not listed under Microsoft 365 but want to set up email delivery for it, enable the “Accept mail for all subdomains” option. This is useful for accepting emails to any subdomain of your primary domain.

Step 2: Create a Connector for Email Flow

1. Navigate to Connectors: Under the “Mail Flow” section, select the “Connectors” tab and click the “+” sign to add a new connector.

2. Define Email Flow: Set the flow condition with “From” as Microsoft 365 and “To” as Your organization’s email server. Proceed by clicking “Next.”

3. Name Your Connector: Provide a name for the connector for easy identification. Optionally, add a description. Ensure options “Turn it on” and “Retain internal Exchange email headers” are selected.

4. Specify Domains: Choose “Only when email messages are sent to these domains” and add your domain name by clicking the “+” button.

Step 3: Configure Smart Host for Secondary Service Delivery

1. Enter Smart Host Details: You’ll need to specify a smart host (e.g., priority 1 MX record of Google Workspace) where Microsoft 365 will route emails. This can be an IP address, FQDN, or MX record. For Google Workspace MX records, visit: Google Support

2. Enable TLS: Keep TLS enabled for secure email delivery and proceed.

Review the configuration details to ensure everything is set up correctly, then click “Next” to continue with the process.

Step 4: Testing and Finalizing the Setup

1. Test the Connector: You’ll be asked for an email address associated with the secondary service (not an Exchange mailbox) to test the connector.

2. Validation: After a successful test, a confirmation screen will appear. Save the connector setup.

Additional Steps:

  • Hydration Process: Post-setup, allow up to 12 hours for the changes to take effect. To expedite, use PowerShell to connect with Exchange Online and run Enable-OrganizationCustomization.
  • Troubleshooting: If you encounter delivery issues, ensure the domain is set as Internal Relay, the connector is turned on, and adjust your DMARC policy to “none” if it’s set to “reject.”


Setting up email split delivery between Microsoft 365 and another email service, such as Google Workspace, ensures a smooth transition and uninterrupted communication for your organization. By following the detailed steps outlined in this guide, you can successfully configure your email systems to work in harmony, regardless of whether emails are hosted on Microsoft 365 or another platform. This setup not only enhances the flexibility of your email infrastructure but also allows you to tailor email delivery to meet specific organizational needs or user preferences.