I'm working with Outlook 2010 and Exchange 2010 and while writing this post I found another post on the topic but it was for Exchange 2007. It mentioned Address List Segregation which, as it turns out, is not supported in Exchange 2010. So it seems another method is required.

I've successfully hidden a distribution group from the GAL by removing the Authenticated Users group but the group is still visible in the Address Book called "All Groups". I would expect it to be hidden in all address books not just the GAL. Are there any other security groups I should remove to hide it from All Groups?

To give visibility in the GAL I am manually adding the user (the group is being used for Send As purposes).

In the image below the green line represents where the group is visible and the red line indicates the opposite.