Mailbox filtering.

[wafer]

I have an existing mailbox on my exchange server, which I need to filter the messages going to it. I only want to stop email being received by the mailbox if the message has also been sent to someone else in either the "To" or "CC" boxes. I would like the account to receive mail though if it is the only recipient of the message. The mail account is used by a helpdesk system, so I do not want it not to receive email when someone sends a message to the whole address book.
Please Help anyone..