[Exim] How do I limit some users to the local domain only?

Dear all

I'm a new subscriber to this list with a stack of questions I would like to answer before enabling Exim on our school server
(FreeBSD 4.5RELENG.)

My first question is: What should I use as a search string in the archives search engine to see if this question has come up
before, viz. How can I set up Exim to limit some users to local deliveries only, while allowing other users in the same domain
full Internet mail facilities?

Within the school, we wish to allow admin and teaching staff full Internet mail (via Outlook Express), while the pupils should
only be able to send to addresses within the local domain (perhaps limited to certain addressees only.)

Thanks in advance!

Martyn Hill
ICT Teacher and IT Co-ordinator
St James Independent School