Google Message Archiving Microsoft Exchange Journaling Configuration Guide For Exchange Server 2007 and 2010 - Manual (Page 24)

26 Message Archiving - Microsoft Exchange Server 2007 and 2010 Journaling Configuration Guide
Set-Mailbox AMaster -HiddenFromAddressListsEnabled $true
Step 7: Prevent Mail from Going Directly to the Journaling
Mailbox
In Step 2, you set up the journaling mailbox. You now need to set up a delivery
restriction for the
AMaster user to prevent anyone from sending email messages
directly to the journaling mailbox.
To set the delivery restriction:
Use the Set-Mailbox cmdlet to modify the settings for the journaling mailbox to
prevent anyone from sending email messages directly to the that mailbox. Issue
the following command:
Set-Mailbox AMaster -AcceptMessagesOnlyFrom AMaster