How to Setup an Alias, Additional Email Address, or Change Addresses

In your Control Panel
Click on the name of your Hosting Plan (typically Exchange Hosting, SharePoint Hosting, etc)
Click Hosted Organizations
Click your domain name
Click Mailboxes
Select your Mailbox
Select the Email Addresses tab

Adding Addresses
Enter the new Email Address and select the appropriate domain
You may use your own domain or the built-in domain

Changing Your Primary Address
Select the new Email Address and choose Set As Primary
This will also change your username for Outlook and Outlook Web Access