Block meeting requests from outside the domain

I need to block the text in the message body of a meeting request (sent from Outlook) to be seen by anyone who has permissions to another user's calender.  I have a situation where a manager is frequently receiving meeting requests (from users outside his domain) with sensitive data in the message body.  His calender is shared to many users, so if he accepts that meeting request, all those users can see the message body.

If this cannot be done, the second option would be to block all meeting requests sent to a user (or all users in my domain) from anyone outside my domain.  I don't want the email for the request to show up in anyone's Outlook.

I would like to avoid using Outlook Rules because the manger does not always access his email through Outlook.

Active Directory 2003 domain, with Exchange 2003 SP2 and Outlook 03/07.
Who is Participating?
Your problem is not a technology issue but rather a user training issue.  It sounds like this manager is improperly sharing his calendar because he does not know any better.

The manager should sharing his calendar only with a small number of trusted users (such as an administrative assistant who helps with scheduling).  As a general rule "many people" should not be getting the meeting requests, so should not be in the share list.

If the manager needs to have some other trusted people have access to open his calender, permissions should be set accordingly on the calender folder.  This is NOT sharing -- it is setting up permissions in the properties of the calender (right-click calendar folder, select properties, go to permissions tab).

People who are not trusted enough to see each and every item in the managers calendar should only have default free / busy permissions.  This allows them to easily schedule a meeting with the manager without having to know what the manager is actually doing during "busy" times.

HopperSIAuthor Commented:
Everyone with permissions to view his calender needs to have it for scheduling reasons.  Once he accepts a meeting request, the message included with it is displayed in his calender, and anyone with permissions can see it. It is only necessary for users to see an appointment at that time, not the message.  If this is not possible, I would like to block all meetings requests sent from email address outside my domain.
Making Bulk Changes to Active Directory

Watch this video to see how easy it is to make mass changes to Active Directory from an external text file without using complicated scripts.

mds-cosConnect With a Mentor Commented:
"Everyone with permissions to view his calender needs to have it for scheduling reasons."  So you are saying that everybody goes to the same meetings that this manager is invited to -- or for some reason should have all of his meetings show up for them?

I question this because all to often I see people "share" their calender because the lack basic understanding of what this is for.  They somehow think that they need to share the calender so that people can schedule meetings with them.  This is patently untrue.  Go to schedule a meeting and invite the manager as an attendee.  Exchange will automatically show you when the manager is busy and when he is not -- without revealing the details of any of his meetings.

"It is only necessary for users to see an appointment at that time, not the message."

This is basically what I am trying to get at.  Users can see the fact of an appointment if they use Outlook tied into Exchange properly -- this does not mean somebody sharing their calender.
Please provide a reason why the answers give are not acceptable.  Both I and FearNoMore tried to give you ways to accomplish your goal within the realm of what Outlook does and does not do.
Question was answered by one or more Expert comments:

FearNoMore -- comment 2 -- provided one approach of marking each item as private.

mds-cos -- comment 1 -- provided another approach of sharing only with people who really need shared access, and having other people use the free/busy time for scheduling rather than having full access to the calendar items.
All Courses

From novice to tech pro — start learning today.