Redirecting mail

Rob Sterenborg rob at sterenborg.info
Fri Apr 8 12:58:20 CEST 2005


> Now what i would like to know is there a way I could route 
> all out going mail from 172.20.128.56 to 192.168.16.56 using
> iptables DNAT.
>
> First of all, is it possible to do what I want to do? and 

The networks seem to be connected, so can't you just configure a
smtp-forwarder in your MTA configuration ? That would be easier I think.

> would I use iptables or iptables with something else?

No, just iptables would be enough.

> This is what ive tried...
> 
> on 172.20.128.56 (Red Hat Linux release 7.3)
> i issue the command  : 
> iptables -t nat -A OUTPUT -p tcp -m multiport --dports smtp 
> -j DNAT --to-destination 192.168.12.56

There is no need to use multiport because you only DNAT 1 port : smtp.
But that should not be a problem.

iptables -t nat -A OUTPUT -p tcp --dports smtp \
-j DNAT --to-destination 192.168.12.56

> now when im on 192.168.12.56 (Red Hat Linux release 9 (Shrike) )
> and do a tcpdump greping for smtp I see connections from 172.20.128.56
> but not exactly sure what its doing.. but what i know, from  
> 172.20.128.56 I cant make smtp connections out to the internet..

A few obvious tests :
Do you see mail coming in from 172.20.128.56 into the queue of
192.168.12.56 ?
Is mail from 172.20.128.56 "for the internet" being delivered ?

If it's not working, do you have other iptables rules that prohibit this
from working ?


Gr,
Rob




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