In this exercise we will setup sending mails but this will be filtered with DNS record. I hope that you don't remove your configuration for DNS which we made before. On both machine you should setup that themselves use your DNS. According to this you should change /etc/resolv.conf

search setenforce.com my domain
nameserver 192.168.0.120 IP address for name server

to be sure this is working I will start next command:

[root@security2 ~]# host client
client.setenforce.com has address 192.168.0.20

You should add rule to DNS, so in setenforce.internal (look on next link DNS setup) add next:

20.0.168.192.setenforce.com. IN A 127.0.0.2

and in sendmail.mc file you should add next:

FEATURE(`dnsbl', `setenforce.com', `"550 Message from "$&{client_addr}" blocked." ')dnl

Restart both service and try to send mail from security2. Now you will got something like this:

...
550 5.7.1 Message from 192.168.0.20 blocked.