How to Use Microsoft 365 Email and Third-Party Server Email Together
Question details
The user wants to host specific email accounts on Microsoft 365 and other accounts on a third-party server under the same domain to save on licensing costs.
- Product
- Microsoft 365
- Device & OS
- not provided
- Scenario
- Setting up email coexistence between Microsoft 365 and another hosting provider for different users sharing a single domain.
- Observed behavior
- Simply adding multiple MX records does not split email routing. Explicit internal relay and connector configurations are required to deliver mail correctly across both servers.
Ensure you have Global Administrator privileges for your Microsoft 365 account and access to the DNS management portal of your domain registrar to modify MX records.
Configure Email Coexistence Using Exchange Admin Center
Set up Microsoft 365 as an Internal Relay to route mail to your third-party server for any unrecognized email addresses.
To use Microsoft 365 and a third-party email server together, you cannot simply use multiple MX records to split the mail. Instead, you must point your domain's primary MX record to Microsoft 365, configure your domain as an Internal Relay, and create an outbound connector to route emails for non-Microsoft 365 users to your third-party server.
Confirm with your third-party hosting provider that their server supports mail forwarding and coexistence, and obtain the Smart Host IP address or domain name required for routing.
Log into the Microsoft 365 Exchange Admin Center. Navigate to 'Mail flow' > 'Accepted domains'. Select your domain, change the domain type from 'Authoritative' to 'Internal Relay', and save the changes.
In the Exchange Admin Center, go to 'Mail flow' > 'Connectors'. Add a new connector from 'Office 365' to 'Your organization's email server'. Enter the Smart Host IP address or FQDN of your third-party server.
Log into your domain registrar's control panel. Update your primary MX record to point exclusively to Microsoft 365 (e.g., yourdomain-com.mail.protection.outlook.com). Remove any existing third-party MX records.
Send test emails from external addresses (like Gmail) to both a Microsoft 365 mailbox and a third-party mailbox on your domain to verify that mail routes correctly through the Exchange connector.
Manage Your Documents Effectively with WPS Office
While setting up complex email routing to save on Microsoft 365 licensing, you can further optimize your software costs by switching to WPS Office. It provides robust tools for all your business documentation needs without heavy subscription fees.
- 1. Download the software: Visit the official WPS Office website and download the free installation package.
- 2. Install on your device: Run the installer and follow the quick on-screen prompts to set up the software.
- 3. Open existing files: Launch WPS Office to immediately open, edit, and save your existing Office documents.
Frequently Asked Questions
Can I use multiple MX records to split mail between Microsoft 365 and another host?
No. A single MX destination does not automatically split mail. Secondary MX records are used for fallback if the primary server goes down, not for splitting active users. You must configure mail routing and connectors to achieve coexistence.
What is an Internal Relay in Exchange Online?
Internal Relay is a domain setting in Microsoft 365 indicating that if a recipient is not found in your Microsoft 365 user directory, the Exchange server should forward the email to another specified server (like your third-party host) rather than bouncing it back as undeliverable.
Do I need a specific license to set up email coexistence?
You must have an Office 365 or Microsoft 365 subscription that includes Exchange Online (such as Business Basic, Standard, or Premium). This gives you access to the Exchange Admin Center required to configure the necessary internal relay and outbound connectors.
