HowTo: Exchange 2013 – Give admin access to all mailboxes. Disable Automapping.
Open the Exchange Management Shell and type in:
Get-Mailbox | Add-MailboxPermission -user gmatteson -AccessRights FullAccess -InheritanceType All -AutoMapping $false
In Exchange 2010 Service Pack 1 (SP1) Exchange introduced a feature that allows Outlook clients to automatically map to any mailbox to which a user has Full Access permissions. If a user is granted Full Access permissions to another user’s mailbox or to a shared mailbox, Outlook automatically loads all mailboxes to which the user has full access.
To accomplish this, Exchange populates the msExchDelegateListLink attribute in Active Directory to locate mailboxes for which the user has Full Access permission, and then provides this information to the Autodiscover service. Autodiscover then populates the AlternateMailbox attribute with the information necessary for Outlook to open the full access mailboxes. If the user has Full Access permissions to several mailboxes, performance issues may occur when starting Outlook. In Exchange 2010 SP1, there was no way to turn this feature off. However, in Exchange 2010 SP2, you can use the Shell to disable this feature.