authentication of domain to manage mail

[yordangs]

hello to everyone i have the next problem i have a mail server who has a few domains working with sendmail all works fine but one of the owners of the domains wants make like a intranet for his domain example

the example_domain only wants accept mail from the example_domain and only wants to send mail to the example_domain how i could do that ?

i neend to restrict this domain but all the rest of the domains continues working normally theres any way to do this or someone have a idea anything will be apreciated

an thanks a lot for the attention and