Add Another Email Alias for a User

Email Address tab

How to add an alias email address for an account?
-Open Email Address tab.
Add the email you want.

How to set the primary address?
-Open email Address tab.
-In the below section you will find listed the emails added to that account
you can click on Primary beside the email that you want to set as primary:

primary mail

Note: the one with the green checkmark is the primary email.