Be aware in Exchange 2007 if a Domain account is disabled the mailbox can still receive emails. This was not the default behavior in Exchange 2000 or 2003. Exchange 2003 however did have a hot-fix which changed its behavior to that of 2007. Please see the link below for more information on this. The point here is to make sure everyone is aware disabling an AD account will not necessarily stop email from being delivered to a mailbox.