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 From:  Chris Buechler <cbuechler at gmail dot com>
 Cc:  m0n0wall at lists dot m0n0 dot ch
 Subject:  Re: [m0n0wall] Outbound NAT
 Date:  Thu, 19 Jan 2006 11:37:48 -0500
On 1/19/06, Richard Parvass <Richard dot Parvass at aaland dot co dot uk> wrote:
> I have a setup where currently a public IP that is different from the
> WAN address is used for SMTP inbound. It is using Server NAT for the
> inbound. Inbound is working correctly. However, when outbound, it
> originates from the WAN address.

that's how it should work by default - server NAT is inbound only.

> How do I configure the NAT so that outgoing SMTP originates on the
> alternate address defined in Server NAT whilst other outbound is
> originated on the WAN address from the same (internal) machine?

You can't be that specific with NAT (i.e. down to the protocol level,
only source/dest IP or network is permitted).  You'll have to set it
up so all outbound traffic from that internal machine gets NAT'ed to
that specific external IP to accomplish that.  Use advanced outbound
NAT, and remember after enabling it, you will have to manually create
the NAT mappings that are otherwise automatic (like the default LAN to
WAN IP mapping, etc.)