You dont manage email by using/adding short names to the user's account.
Every user has their own unique short name. This in effect becomes their email account (it can be something else)
In Workgroup Manager, you need to setup groups - Sales1, Sales2, Sales3, etc. Then add each user to their respective group and then the email for that sales group becomes email@example.com and firstname.lastname@example.org. Also add the manager to the group list and that manager will get a copy of all the mail that group receives.