Mike Cardwell wrote:

> * on the Fri, Jul 14, 2006 at 09:39:56AM +0800, W B Hacker wrote:
> 
> 
>>>>>iptables -t nat -A OUTPUT -p tcp --dport 25 -d ! 127.0.0.1 -m owner ! 
>>>>>--uid-owner exim -j DNAT --to-destination 127.0.0.1
>>>>>Someone might find that useful...
>>>>
>>>>The intent is good, but that specific rule is not necessary on Unix, nor 
>>>>will it 
>>>>block outbound traffic.
>>>
>>>I think you are misreading what that line does.  It redirects outbound
>>>traffic destined to port 25 to localhost port 25.  It does not address
>>>what port the query comes from.
>>
>>I understand what it *attempts* to accomplish.
> 
> 
> Attempts and succeeds...
> 

..in preventing a user from reaching port 25 on a remote host, yes.

In preventing a user from sending mail, no, not by itself, it doesn't.

*snip*

> ... How is this related to the
> initial requirements stated at the beginning of this thread?
> 
> Mike
> 

The OP seeks to block users from sending to external destinations.

More things have to be done to accomplishing that than the rule shown.

Bill






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