External mail block to some users or IP/subnets

I have linux enterprise 4 using sendmail I want to block external domain emails like hotmail / yahoo to some internal users or IP/subnet. although they are sending / receiving internal mails.

 

Please clarify your question, dont you want your users to receive mail from yahoo and hotmail

 

External emails

Yes I want my some users which are on different LAN location also sepearted with different subnets could not received external domains email.