I am receiving second-hand reports that users are able to see hidden mailboxes in the GAL. Apparently these ghosts appear and disappear and I'm unable to diagnose. Any thoughs are appreciated..

First get an example mailbox with this behaviour, then check if it's hidden. After an End User says he/she can see it in GAL (or any other address list) check if it's still hidden. You need a pragmatic approch to this since it might just be End User confusion.Jesper Bernle | Microsoft Community Contributor 2011 Awardee