SO here is the thing, if you are faced with a request that a specific user/group needs full mailbox access to all users and also anyone who is added in the future, you can set a blanket permission to all current and future mailboxes, the way to do it is using the following cmdlet in exchange 2010:
Get-MailboxDatabase -identity “[mailbox database name]” | Add-ADPermission -user [username] -AccessRights GenericAll
You would need run this command again if you add another mailbox database.
Exchange KB 