I would like to allow my users to send Out of Office replies to external
recipients, but only if the sender appears as an entry in the user's personal
Outlook contacts.

I have my Exchange 2007 server set to "Allow external out-of-office messages
only". In Outlook 2007 Out of Office Assistant properties there are two
options on the "Outside My Organization" tab:

"My Contacts only"
and
"Anyone outside my organization"

This is a user selectable option and I would like to prevent users from
being able to select "Anyone outside my organization". In other words, if
the user chooses to send auto-replies to people outside of the organization
it needs to be based on "My Contacts only", not just anyone.

Is it possible to disable the "Anyone outside my organization" option
through group policy, a registry change, or something else?