Create Internal mail that only allows email with two domains

[darthabingdon]

I grabbed mailenable for an attempt to work on a little side project. We would like to make it so we could use it as an internal mailserver for our employees to communicate with each other. My question is is it possible to restrict the server so that users can only email 2 domains? One is our public facing mailserver, the other is the mailenable server. If it isn't possible no worries, I'll look for something else.