What that tip says is this :
1. Create a Group named, e.g., "Mail Password" and add your own name to the member list.
2. In the Internet address field, put the password followed by your domain, e.g., 987654@yourdomain.net
3. Save the group document.
4. Create a Domino Mail Rule in the Configuration document with this content.
5. If "To or cc" is All Company and "bcc" is not 987654@yourdomain.net, don't accept the message.
Now I am not an admin, so I might be missing something, but when it says "All Company", is that a group name, or a Rule setting ? Because if it is a group name, then once again, this Rule will not prevent someone creating a personal group with everyone in it, or simply using the Address button and selecting everyone.
Pascal.