[Exim] relaying?

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Hello.

I have a Exim 3.36 server and it handles the domain reboot.nu
The problem I have is that is "relays" mail for other domains aswell, I have seen *@yahoo.com and other
addresses sending mail thru my system. How do I change so that it only accepts *@reboot.nu for outgoing mail
thru exim?

I want everyone to be able to send mail thru my system, as long as they have a *@reboot.nu domain in their email address.

//Jonas
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