How to Add a New Email Domain and Keep the Old as an Alias in Microsoft 365
Question details
The user needs to add a new custom email domain in Microsoft 365, make it the primary address for users, and retain the previous domain address as an alias.
- Product
- Microsoft 365
- Device & OS
- not provided
- Scenario
- An organization is updating its email addresses to a new domain but wants to ensure that emails sent to the old addresses are still successfully received in the same mailbox.
- Observed behavior
- Users will send emails from the new primary domain, and any messages sent to either the old or new address will be delivered to the same user mailbox.
Ensure you have Global Administrator privileges in Microsoft 365 and access to the DNS settings of the new domain you intend to add.
Set up a new primary domain and retain the old one as an alias
Use the Microsoft 365 admin center to verify your new domain and update user primary addresses without losing the old address functionality.
When you change a user's primary email address, Microsoft 365 automatically keeps the previous email address as an alias. This guarantees uninterrupted email delivery during domain migrations.
Log in to the Microsoft 365 admin center. Navigate to Settings, then click on Domains. Add your new custom domain and follow the prompts to verify it using DNS records.
In the left-hand navigation menu of the admin center, go to Users, and then click on Active users.
Select the users whose email addresses you want to update, and choose 'Change domains'. Select the newly verified domain to set it as the new primary address.
Save your changes. The previous email address will remain as an alias by default, ensuring that messages sent to either address will reach the same mailbox.
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Frequently Asked Questions
Will users lose their old emails when the primary domain is changed?
No, changing the primary domain and keeping the old one as an alias does not affect existing emails. All historical data remains perfectly intact in the mailbox.
Can users reply from their alias email address in Microsoft 365?
Yes, Microsoft 365 supports sending emails from an alias. Administrators can enable this feature in the Exchange admin center under Settings > Mail flow.
How long does it take for the new primary email address to take effect?
Domain changes and alias updates usually take effect within a few minutes, but it can occasionally take up to 24 hours to fully propagate across all Microsoft 365 services.
Do I need to pay for an extra license for the alias address?
No, aliases are included in the user's existing Microsoft 365 license. You can add up to 400 aliases per user without purchasing any additional licenses.
