Exchange Connection Problems

How to Set Up Multiple Domains and Email Aliases for One Microsoft 365 User

Maira Mehtab Sep 21, 2026 868 views

Question details

The user needs to configure multiple custom domains and assign multiple email addresses (aliases) to a single licensed Microsoft 365 user, allowing them to share one mailbox without extra licenses.

Product: Microsoft 365 Business Standard / Premium
Device & OS: not provided
Scenario: Managing custom domains and reducing licensing costs by utilizing email aliases for different domains.
Observed behavior: Messages sent to aliases are delivered to the primary mailbox, but users also need the system to allow sending or replying directly from those specific alias addresses.

Before you start

Ensure you have Global Administrator privileges in your Microsoft 365 tenant to verify new custom domains and execute Exchange Online PowerShell commands.

Solution 1Recommended

Add Custom Domains and Assign User Aliases

Add your secondary domains to the Microsoft 365 tenant and assign the new addresses as aliases to the primary user.

Microsoft 365 allows you to host multiple custom domains within a single tenant. By assigning addresses from these secondary domains as aliases to an existing user, you avoid paying for additional user licenses.

Verify custom domains

Log into the Microsoft 365 admin center. Navigate to Settings > Domains, and follow the prompts to add and verify your additional domains (e.g., mydomain1.com, mydomain2.com).

Select the primary user

Go to Users > Active users and click on the licensed primary user who will manage these emails.

Add the alias addresses

In the user pane, click 'Manage username and email'. Add the new alias addresses, making sure to select the newly added domains from the dropdown menu, and save your changes.

License Optimization: Incoming messages for these newly created aliases will now be delivered directly to the primary user's mailbox without requiring any separate Microsoft 365 licenses.

Solution 2

Enable Sending from Aliases via PowerShell

Configure your tenant to allow users to send outbound emails using their alias addresses.

Solution 3

Contact Microsoft Support for Backend Review

Escalate the issue if alias delivery or sending capabilities remain dysfunctional after correct configuration.

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Frequently Asked Questions

Do I need to buy a separate license for each email domain alias?

No. You can add multiple email aliases from different verified domains to a single licensed user account. All emails sent to those aliases will flow into the same inbox without triggering additional licensing fees.

Why are my email replies sending from my primary address instead of the alias?

By default, Exchange Online uses the primary address for all outbound mail. To fix this, a Global Admin must enable the 'SendFromAliasEnabled' setting using Exchange Online PowerShell, after which you can select the alias in the Outlook 'From' field.

How long does it take for the PowerShell alias setting to take effect?

Changes made via Exchange Online PowerShell, including enabling the send-from-alias configuration, can take anywhere from a few minutes to a few hours to fully propagate throughout the Microsoft 365 servers.

Outlook & Email Problems