How to Create a User Mailbox in Exchange Online

Overview

A user mailbox in Exchange Online stores a user’s email, calendar items, contacts, and related collaboration data. To provision one, you create a user account (typically via the Microsoft 365 admin center) and assign an Exchange-capable license. Once the license is active, the mailbox is automatically created. This approach is supported by Microsoft documentation. Microsoft Learn+1

Steps

Step 1 — Create the user account via Microsoft 365 admin center

1. Sign in to the Microsoft 365 admin center (at admin.microsoft.com) with appropriate admin permissions (e.g., User management admin or Global admin). Microsoft Learn+1

2. Navigate to Users → Active users → Add a user. Microsoft Learn

3. Fill in required details: display name, username/UPN (e.g., alice@contoso.com), select the domain, set password options. Microsoft Learn

4. On the product license page, choose a license that includes Exchange Online, select additional apps if needed. Microsoft Learn+1

5. Finish the user creation process by reviewing and confirming. The user account is now created.

Step 2 — Assign an Exchange-capable license

1. In the user’s properties (or during creation), assign a license that includes Exchange Online (e.g., Microsoft 365 Business Standard, E3, E5).

2. Confirm that the license status shows assigned and active.

3. Once the license is active, Exchange Online services will begin mailbox provisioning. The official doc notes “a new user account … when you assign the user account a license for Exchange Online, a mailbox is automatically created for the user.” Microsoft Learn

Step 3 — Verify the mailbox exists in Exchange Online

1. Open the Exchange Admin Center (EAC) at admin.exchange.microsoft.com (or via admin center → Exchange).

2. Navigate to Recipients → Mailboxes and search for the user.

3. Confirm the mailbox appears as “User mailbox” and shows Active status.

4. Note: The Microsoft documentation states there's a propagation time of at least 24 hours in some scenarios after the license assignment before the mailbox is fully available. Microsoft Learn

Troubleshooting & Important Notes

• If the mailbox doesn’t appear, wait up to 24 hours and verify that the license is assigned correctly. Microsoft Learn

• Ensure the user’s UPN uses a verified domain in your tenant to avoid provisioning issues.

• For users synchronized from on-premises (via Azure AD Connect), follow hybrid provisioning rules rather than creating duplicate users directly in the cloud.

• When using PowerShell to create the mailbox (advanced scenario), remember you must assign a license afterward or the mailbox will be disabled after the 30-day grace period. Microsoft Learn

• Use least-privilege admin roles when creating users; avoid using Global Admin routinely unless necessary. Microsoft Learn