I want to limit the number of hosts that can relay email.
In Exchange I can say only relay from 192.168.0.10, 192.168.0.20, and only for mydomain.com.
Why? Lets say someone gets a virus or rogue application on their computer I don't want these computers sending email. Currently I can log onto any computer on the local subnet and send an email from myself to anyone without authenticating.
I've tried using 127.0.0.0/8 192.168.0.10/32 192.168.0.20/32
under the MTA and no luck.