[exim] Router configuration for mailman

I'm new to Linux and I have successfully deployed mailman with Exim4. I want
to configure mailman router to accept post from only local domain i.e.
users@???, we have 450+ email accounts and some users are using Gmail,
yahoo and other webmail for pop account. What router configuration do I
choose??? Which allow emails from only local server i.e. abc.com and rejects
mail from webmail pop accounts and emails which are sent from scripts as
well.



Following are the details of my mailman,

List1@???

List2@???

List3@???



Email clients locally used MS outlook and Mozilla thunderbird.



I want that all 3 list member cannot send post to their list from their pop
account from Gmail, yahoo etc.

Please advise.