blocking certain domains, not acting as a relay

[Simon Karpen <slk@karpes.stu.rpi.edu>]

i've been digging thru zmailer looking for such (fairly new to zmailer but
familiar with *gasp* *barf* sendmail, aka /usr/lib/sendcertadvisories)

anyhow, how does one go about setting zmailer up not to act as a mail
relay for other domains? i'd like to only accept mail that is destined for
local users or aliases, and maybe (for a different machine) accept mail
going to anywhere but only from certain machines, and mail from anywhere
but only going to certain machines. 

i'd also like to know the easiest way to block out a couple of domains
(earthstar.com comes to mind) to get rid of at least some of this UCE at
the source, as all users on the particular system(s) want it to be
blocked. 

Thanks, and I've tried to RTFM but there really isn't much of a FM. 

Simon Karpen
karpes@rpi.edu, slk@acm.rpi.edu, slk@karpes.stu.rpi.edu
When you say "I wrote a program that crashed Windows", people just stare at
you blankly and say "Hey, I got those with the system, *for free*"
	--Linus Torvalds