[Exim] Preventing mail deliveries

Hi there.

I have Exim running on a slackware 7.0 server. I have 120 users that
require local mail
only. Of the 120 users, only 20 require the ability to receive and
send internet mail.
I have set up the server so that everyone can send and receive mail
internally and externally.
I am using dial-up and Fetchmail and have a domain registered. All
mail for our domain is
dropped into a pop3 account without the origional "TO" address being
changed.

How can I restrict the other 100 users from being able to send mail
out and how do I make them
unable to receive mail from other domains? Users are checking their
email addresses and sending
email to that address from home etc. Internet mail & browsing we want
to keep restricted to managers
and heads of departments until we can get a permanent line in.

I have made 2 mail domains and set up a relay policy that won't allow
"non-local" relaying for
one of the domains. This has prevented the 100 users from mailing out
of the network. They get a
message saying that relaying has been denied, contact your
administrator. I cant use ip based relay
rules because all the clients go through a Citrix server. The drawback
to this solution is that
they can get around this if they change their from address in their
mail client and it doesnt prevent
them receiving outside mail.


Does anyone know of a "better" way of doing this?
Many thanks
Gary


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