[Exim] Multiple domains question

Hi to all,

I have configuration for two domains on the same Exim mailserver,
domain1.com and domain2.com, and I have one user boris.
When I send mail to boris@??? and to boris@???
there are all going to same mailbox. Also I have a unique list of users.

How can I prevent this, bicouse I don't need mail for boris@???
to be accepted, but for some other user, for example, dragan I need to
receve mail for dragan@??? but no for dragan@???


Thanks in advance