From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Rob Sterenborg" <rob@sterenborg.info>
Subject: RE: How to block sending mail from local network.
Date: Sat, 7 Feb 2004 21:17:32 +0100
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> I want to block smtp operations from the local network so the 
> viruses/worms will be blocked.
> 
> I tried a command:
> $IPTABLES -A OUTPUT -p TCP -i $LAN_IFACE -s $LAN_IP_RANGE 
> --dport smtp 
> -j DROP
> but it did nothing.

No, the INPUT and OUTPUT chains are for filtering the local machine : de
firewall itself.
If you want to block clients, you should use the FORWARD chain.

You could use a rule like this one :
$IPTABLES -A FORWARD -i $LAN_IFACE -s $LAN_IP_RANGE -p tcp --dport 25 -j
DROP
or
$IPTABLES -A FORWARD -i $LAN_IFACE -s $LAN_IP_RANGE -p tcp --dport 25 -j
REJECT --reject-with tcp-reset

I suppose you're running your own mailserver ? Otherwise none of your
clients are able to send email.


Gr,
Rob