How to Use Office 365 and cPanel Email with the Same Domain
Question details
The user needs to configure a split-delivery email system where some mailboxes are hosted on Microsoft 365 and others on cPanel, allowing all users to send and receive internal and external emails using the same domain.
- Product
- Microsoft 365 / cPanel
- Device & OS
- not provided
- Scenario
- Establishing email coexistence across two different hosting environments without relying on simple email forwarders.
- Observed behavior
- Previous attempts using Exchange connectors failed to correctly route and relay mail to the internet and internally across the two platforms.
Ensure you have administrative access to your domain's DNS records, your cPanel hosting account, and the Microsoft 365 Exchange Admin Center before making changes to mail routing.
Configure Internal Relay and Exchange Connectors
This method establishes direct server-to-server routing by setting up connectors in Exchange Admin Center, avoiding the need for individual forwarders.
To achieve true coexistence without forwarding rules, Microsoft 365 must be configured to recognize the domain but understand that it does not host all the mailboxes. This is done by changing the domain type to 'Internal Relay' and creating a connector.
Log in to the Exchange Admin Center. Navigate to 'Mail flow' > 'Accepted domains'. Select your custom domain, change its type from 'Authoritative' to 'Internal Relay', and save your changes. This tells Microsoft 365 to look elsewhere if a mailbox isn't found locally.
Go to 'Mail flow' > 'Connectors' and add a new connector. Choose 'Office 365' as the sender and 'Your organization's email server' as the recipient. Enter your cPanel server's IP address or hostname as the smart host.
Log in to cPanel, navigate to 'Email Routing', select your domain, and change the setting to 'Local Mail Exchanger' if cPanel is handling the MX records directly, or configure Exim to smart-host outbound mail via Microsoft 365 if Microsoft handles the MX.
Ensure your domain's SPF (TXT) record includes the IP addresses of both Microsoft 365 (include:spf.protection.outlook.com) and your cPanel server to prevent outbound emails from being marked as spam.
Pilot Microsoft 365 using Forwarding Rules
If connectors are too complex or fail to authenticate, Microsoft's official pilot method uses a routing subdomain and forwarders to bridge the two systems.
Experience a Seamless Office Alternative with WPS Office
While configuring complex email infrastructures like Microsoft 365 and cPanel split delivery requires intensive IT administration, choosing the right office productivity suite doesn't have to be difficult. WPS Office provides a lightweight, highly compatible, and free alternative to Microsoft Office, ensuring your teams stay productive regardless of their email backend.
Frequently Asked Questions
What is email split delivery or coexistence?
Split delivery is an email configuration where users sharing the exact same custom domain have their mailboxes hosted across two different servers, such as Microsoft 365 and cPanel. This allows both groups to email each other and external contacts seamlessly without changing their email addresses.
Why do internal emails fail between cPanel and Office 365?
This usually happens because cPanel is configured as a 'Local Mail Exchanger'. When a cPanel user emails a Microsoft 365 user on the same domain, cPanel attempts to deliver the mail locally and fails because the mailbox doesn't exist there. Changing cPanel's Email Routing to 'Remote Mail Exchanger' often resolves this.
Can I relay cPanel outbound mail through Microsoft 365?
Yes, but you must configure an inbound connector in the Exchange Admin Center that authenticates your cPanel server's IP address. Additionally, you must update your domain's SPF record to authorize both environments to send mail on your behalf.
Should my domain be Authoritative or Internal Relay in Office 365?
For a split delivery setup where some mailboxes live on an external server like cPanel, the domain in Office 365 must be set to 'Internal Relay'. This setting forces Office 365 to forward emails intended for unknown users to your secondary server via your configured connectors.
