Exchange 2010 - Need to prevent random domain aliases from being created on mailboxes - Helpdesk added imaginary domain aliases to users... Business cards were made...

Murphy strikes.<o:p></o:p>

We own a domain e.g. newcompanyINC.com (was available for purchase)<o:p></o:p>

Users request alias newcompany.com (was not available for purchase)<o:p></o:p>

Helpdesk adds bad alias to 50 accountsuser@newcompany.com vs good alias user@newcopmanyINC.com 
- Works internal? Does not work external...<o:p></o:p>

Usual end-user complaint about not getting mail and 2 hours latter voila! <o:p></o:p>

I assume this is related to our migration from zimbra to exchange last year... I assume we had to do something to allow non-authoritative domains to be used for aliases... I assume that this allows random aliases to be added to a mailbox...<o:p></o:p>

So... Zimbra would not have allowed the helpdesk to add an alias for a non-existent domain. Is the exchange behavior normal and unchangeable, default and changeable or migration related hack that needs undone?<o:p></o:p>