In response to "Jonathan Hunter":
> I want to be able to allow users of local machines to be able to use it as a
> relay to send outbound mail - this part is easy. The tricky part is that
> some of the local machines are public-access machines. Potentially somebody
> could use a public machine to relay thousands of messages out through Exim.
Do you mean that the public-access machines could run a mailer that
will act as an open relay? Or that someone might _originate_
unsolicited bulk mail from one of those machines? If it is the first,
then I would suggest proper controls on what software is put on those
machines! If the second, controls on who goes near the machines would
be in order; you don't define "public access" so do you mean your own
students for example?
> This problem would seem to be similar to an ISP with dialup users - the
> dialups would be considered local and allowed to relay through Exim, but the
> ISPs wouldn't want their dialups to be able to send spam to the outside
> world.
>
> How do the big ISPs do it? Are there some rules that can be put in place to
> reject spams like this?
Our solutions at Demon Internet Netherlands are "political" rather
than technical. If we find evidence that anyone has got an open relay
(even on a dial-up, if the person is logged in for a while, an open
relay can be found by senders of unsolicited mail), or a complaint is
made about the sending of unwanted bulk mail, then, after making the
relevant checks, we close them down temporarily or permanently. The
equivalent in a university would presumably be disciplinary
procedures. We don't do anything to try to stop them sending the mail
in the first place -- after all, someone running a small business
might have a legitimate need to contact thousands of customers who
have _asked_ to be put on a mailing list.
This has got nothing to do with configuring Exim so I shan't say any
more than that.
