Our environment has many shared mailboxes, resource mailboxes, mailboxes opened as secondary (admins for execs, etc.). I noticed that, when moving a shared mailbox from Exchange 2003 - 2007, the user who opens that mailbox as a secondary mailbox cannot access it until I set the mailbox permissions through the Exchange 2007 admin console. I would have thought that these permissions were purely in AD. Could someone shed some insight on this please? This greatly complicates our mailbox migration plan as now we need to document each and every user that has a secondary mailbox and assign permissions immediately post-move.