Stopping users from sending internal email?

You can stop them from sending Internet EMail by not loading the Internet EMail service within Outlook.

We want to stop them being able to send internal emails.

Oops.  I read that one wrong.  That's a bit weird, but I would suspect it to be possible.  I can't find anything on it, though.  Sorry about that.

Set you people up with Internet mail only, not corporate/workgroup mode.  This will only slightly deter them from sending to each other, because there is NO WAY to restrict them by SMTP address unless you remove it entirely, then they cannot send Internet email.

If you set it up with IMO then it won't use the Exchange Server at all.

Just as you add the smtp address for the user, you can take their mail address away from them. The problem you will have is that while you can remove the other mail handlers, if they can receive mail from SMTP, then they will. Nothing seperates internal SMTP from external SMTP. What your asking is not possible for the simple reason that Internet email is of a higher order than the regular internal email. You can stop them from sending, or receiving Internet email, but once they have it, all mail can be directed through it, even if it originates from inside. The SMTP email that resolves to a internal address will never go out to the internet, it will just be deposited in the internal mailbox. So the answer is that what you want to do can not be done.

The 'reject messages from' option that is on the delivery restrictions tab.