[exim] How I can block send mails to other domains.

Dear Friends,

I am using exim 4 in my RHEL 4 server I hosted many domains on this
server. One of our domain holders needs these settings.
He would like to send and receive on his domain only eg: He would not
allow his users to send mails to yahoo.com or gmail.com.
But this settings only for his domains only other users need normal
settings. Can I do this with exim mail server? Please help me.

Thanks & regards,
Saju.