[Exim] Different host_reject for each local user?

Hi,

Im maintaining some addresses only for email forwarding for my friends,
so i want that each of theses addresses is only used by its respective
owner, for example:
only friend1 can do forwarding thru user_fw_1@localhost
only friend2 can do forwarding thru user_fw_2@localhost
..etc..
How can i define a diferent reject policy for each local address?

thanks
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P°$@°4u?