[Exim] Restricting local users from sending external mail

Hi All,

By reading the Q9802, it seems that Exim can restrict local users from
sending external mail. I am new with the Exim, and currently using
sendmail for corporate email servers. I wonder if I have several
domains, one of my local user domain is SomeUser@??? and he is
allowed only sending email locally with the exception to 'bcd' & 'cde'
domains. How can I achieve this?

Best Regards
Gene Leung