Windows

I think the easiest approach, and pardon me if you desagree, is to create new distribuition list that more accurately targets the right groups in your organization, then just educate the users to do so. What you do if a user insists on using the wrong list after you create the new lists, just keeping on sending a copy of the original message explaining the new system with a note that the user might have overseeing it.
It works!
Good luck!

Simple answer first, to unhide the DL within Exchange Administrator select the container where the DL's exist (normally 'Recipients') then click 'View' from the Toolbar and then select 'Hidden Recipients'.
Now to Question 1. To stop people emailinga DL you use permissions. To do this from Exchange Administrator open the Distribution list and select the 'Delivery Restrictions' tab. Add users from a 'Hidden'DL to the accept messages from or just the individual mailboxes. This means that only these people will be able to send to this DL. Other users who send to this DL will recieve a Non-Delivery Report stating that they dont have permission to send to this DL. Hope this helps.

Ok, the answer about unhiding the names worked great, thanks!

However the DL permissions thing I'm having a problem with. If I set myself up to be the only person authorized to send a message to the list, it still rejects me. We set it up so that"These 10 users can send" and in the "Reject" box we put every other user on the list. Am I doing something wrong? This sounds like it should work.

In reverse order:

For Hidden Recipients (including DLs) select a GAL or Recipients container in the left pane, go to View menu and click Hidden Recipients. Hidden recipients of the type indicated in the upper part of the View menu (All, Mailboxes, Dist. Lists., etc.) are now visible in the right pane.

To control who sends mail: Use the Delivery Restrictions tabs on the Properties screen for Dist. Lists and Mailboxes to control who can send and receive. Remember, restrictions on individual mailboxes outweigh restrictions on DLs if they conflict.

Do you have a multi-server organization? if so, wait for replication to complete.

do you have the distribution list in the "accept messages from" side?

it's best to create a test Dl with you as a member, then add you as the only person with rights to use this DL, then put a friend in the "reject messages from" side and test results from both of your machines.

good luck. david