When you don't know it exists.
Unable to find a solution regarding my previous post "Domain specific", I have moved everyone to our primary domain. (So everyone can see all the resources/locations). They are able to retain their previous association by me going in and changing their default sending address. Something I was unaware of and I'd like to inform everyone of, is that when you change a user's domain, it changes all of their "like" aliases to the new domain (automatically, silently). Cool feature, unless you don't know it's doing that. When I changed everyone out of the domain they are "technically" in to put them into a common one, it removed all their aliases for the specific domain they were supposed to have--making them aliases for the new domain. Created all kinds of havoc for my organization, until I was able to go in and recreate the now missing aliases.
Seems to me that this action the system takes, of changing the aliases silently, should be changed to giving the choice of action to the user. Or at least warn of the pending change.