Windows 2003 Server with Exchange 2003.
All mail boxes have been migrated from an old server same OS.
Some users mail boxes are available to everyone. They simply have to go to File-Open-Other users folder- Browse to username and it opens.
Not every mail box will open, but there is not a difference in the permissions on the users account or mail file on those that will open and those that won't.
We already edited the registry to show all security on the Exchange System manager, and the permissions are the same as a correctly operating Exchange Server that we compared.