Exchange 2000 Server

Exchange + OS + Dns on same machine.
I have two domain configured.
abcinc.com and xyzinc.com

some of users of abcinc.com should not be able to send a mail to some of users and xyzinc.com and also should not able to recieve mails from some of users of xyzinc.com.
And also same from xyzinc.com to abcinc.com

Can anybody can help me ?

how to configure this ?

Thanks in advance

nirav joshi