Do you want to just send mail between systems on your home network, or send mail to the outside world? Do you want to receive mail from the outside world as well?
If you just want to set up mail on a local network, this is pretty simple. Edit
/etc/hosts on each of your machines to create your own names to map to your IP addresses. So for example you could put this in /etc/hosts on each machine:
192.168.10.1 server1.example.com server1
192.168.10.2 server2.example.com server2
192.168.10.3 server3.example.com server3
and assuming each machine is configured with the given ip address, you could then comunicate between each of them using the server1, server2, or server3 names.