Restrict emails

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we are using RHEL3 with Plesk 8.0.1.

We have domains setup on the server in the following fashion

domain.com
subdom1.domain.com
subdom2.domain.com
*.domain.com

There is one domain among the above which is xyz.domain.com

We require to setup the mailing system in such a fashion that all users on xyz.domain.com can receive emails only from domains on the server VIZ domain.com, subdom1.domain.com, *.domain.com.

Any idea how we can set this up?