Exchange 2007 Clean-MailboxDatabase

When Active Directory accounts are disabled, associated mailboxes are disconnected, but do not show up under the Disconnected Mailxed under Exchange Management console.  Issue the following in the Exchange Management Shell. 

Clean-MailboxDatabase -identity db1


http://technet.microsoft.com/en-us/library/bb124076%28v=exchg.80%29.aspx