Quick tip for Enabling a Mailbox for a user already active in Active Directory.
Launch the Exchange Management Shell (EMS) and run the following command:
- Enable-Mailbox -Identity UserName
Once it runs you will see the info below the command as shown above, to check the mailbox you can run the following command:
As we can now see, the new mailbox is showing under the list of mailboxes.
Hope it helps.