[exim] How to not allow local mail but allow remote mail

Hello,

Yes, I know this is a strange request but I have a special need for a configuration that would deny local-to-loca email while allowing remote email.

In other words:
user1@localdmain to user2@localdomain would be rejected but

user1@localdomain to user2@localdomain, user1@remotedomain would succeed and

user1@localdoamin to user2@localdomain cc user1@localdomain would succeed

In short as long as a local users were sending email to a remote user it will succeed. Only local to local emails would be rejected.

Any suggestions?

Thanks in advance.

Michael