[geeks] anti-spam question

[Mike Nicewonger]

Hi all,

I have been making some attempts to filter spam off may mailservers. One
question I have is this, when configuring the sendmail feature access_db I want
to block all access from some of the country top level domains like .cn, .kr,
.hk, etc.

I have tried putting lines in my access file like this:

cn	ERROR:"550 Get lost spam monkey"
and
.cn 	ERROR:"550 Get lost spam monkey"
and 
*.cn	ERROR:"550 Get lost spam monkey"

this crap is still getting through. So what I want to know is does the
access_db filter by the actual server sending the mail, by the sent from name
(spammer at somelameisp.cn) or via a lookup of the sending server's IP to DNS
lookup?

The sendmail documentation is a large pile of shiH^H^H^help. I seek clue here.
Dispence politely please.

-Mike N