Host The Email Sever Over The Router So That Email Can Be Sent Between The Computer?

can use a network router to network two desktops (windows 8) and two laptops (windows 7, xp) using wired and wireless connection, so that i can share files, printers and use remote desktop and host a basic email sever between the four computer without an internet connection if i can how would host the email sever over the router so that email can be sent between the computer i plan to use mercury mail server and have not got a router yet.