In the Add an alias text box, enter the user name. (This name is the portion of the user’s email address that appears before the @ sign.)
Note: As with any other email address, you can’t reuse an alias that’s already been assigned to someone else, either as a primary address or alias.
If multiple domains have been added to your account, the field to the right of the @ sign is a menu listing available domains. Select a domain for the alias address.
Click Save Changes. It can take up to 24 hours for the alias to become available.