[exim] How to verify and authenticate only for outgoing mail

Hi,

I have exim configured now to verify sender so that when someone tries to
send a mail from one of the domain address that's hosted by the server, they
have to authenticate first and they can only use their own mail addresses.
This works fine for outgoing mail, but now when I try and send a mail from
my hotmail to one of the mail addresses on the server, it gets rejected
because you need to authenticate first.

How do I configure it so incoming mail from the outside world gets delivered
properly while still forcing my mail users to authenticate first before they
can send mail to the outside world?

Thanks,
Theo