1. Sign in to the Google Admin console
  2. Go to the user's account page.
  3. On the user's account page, click Account.
  4. In the Aliases section, click Add an alias.
  5. 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.

  6. 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.
  7. Click Save Changes. It can take up to 24 hours for the alias to become available.