How to Create an Office 365 Mailbox in a Hybrid Configuration

Here’s how to create Office 365 mailboxes using two methods:

1. Add New Users in the Exchange Admin Center (Exchange 2013 and 2016)

This is the simplest way to create an Office 365 mailbox. The process of creating an AD user and setting up the mailbox can be completed in one place and in one step.

The main disadvantage of the Exchange Admin Center is that it only lets you create a new Active Directory account for the user. To create a mailbox for an existing AD user, you’ll need to use PowerShell. Alternatively, you could give that user an on-premises mailbox and then migrate the mailbox to Office 365.

2. Here’s how to get started using the Exchange Admin Center

• Log into the Exchange Admin Center here.
• In the Exchange Admin Center of your on-premises hybrid server, jump over to Recipients > Mailboxes and hit the plus sign right above the “Display Name” column. You’ll notice one of the options is a new “Office 365 mailbox.”

• Complete the information in the Dialog Box and click Save. Once saved, you can edit the user’s mailbox properties to add information such as title, manager, address and phone number.

If you’re creating an Office 365 mailbox this way, there’s no need to set up an AD account for the user beforehand. As part of this process, Exchange automatically creates the AD object for the user in the OU you specify. Simply fill out the details and click save.

• Sync the directory using AD Connect.

On the next synchronization of AD Connect (either automatic or forced), your user will show up in Office 365 and an Exchange Online mailbox provisioned shortly after. Once the user is synced, you’re free to assign the appropriate license to the account.

To force a manual directory sync, log in to the Azure AD Connect server, open an Administrative PowerShell window and execute the following command: Start-ADSyncSyncCycle -PolicyType Delta

• License the User.

1. Browse to https://portal.office.com
2. Click the tiles icon and select the Admin tile
3. Navigate to Users and select Active users
   
4. Select the user in question, locate the Product Licenses field and click Edit
5. Choose a location then click the slider to activate an available license
   
6. At the bottom of the Product licenses pane, click Save

Why Use this method to Create an Office 365 Mailbox?

It is possible to simply create the account in Active Directory and then license that account in Office 365 but creating the Office 365 mailbox this way will not fill in the correct Exchange attributes on the users AD accounts and also with this method you will not be able to see those accounts that were created in AD in the Exchange Admin Center in the on-prem Exchange.

This could also cause the inventory of your on-premises AD Connect domain and Azure AD domain to show incorrect data and conflicting information.