About the only way to do this is to define it in a .pst file in a system share
and only give those three people permission to use that pst file.  The NTSF
file system is the only facility that provides security.  There is no security
inside an Outlook info store.  Remember, Outlook is designed to facilitate the
access to information, not to restrict it.

Hollis D. Paul [MVP - Outlook]
Hollis@outhousebythesound.com
Using Virtual Access 4.52 build 277 (32-bit), Windows 2000 build 2195
http://search.support.microsoft.com/kb/c.asp?FR=0&SD=TECH&LN=EN-US
     
Mukilteo, WA  USA

You could use some code behind the form to check who the user is and disable the Send button. Note that this would not stop a determined user who really wanted to send it.