Exchange mailbox malfunctions
I have a relatively small environment that has, over the years, upgraded from WINNT - WIN2k - WIN2003 & Exchange 5 to 5.5 to 2003.
We recently discovered that any user can access the owner's mailbox (he has administrator rights) by opening another user's folder function. His is the only mailbox that can be opened this way. I have spent hours on a support ticket with Microsoft - no luck.
Under the circumstances, given that you've already contacted PSS and most likely taken a good look at permissions on that mailbox, I would recommend dumping the mailbox to a PST, deleting the mailbox and the user account, and then recreating it.
This was first published in July 2006