Modify sendmail.cf to hide internal IP outgoing mails

Hi,
I have Linux/Debian/sendmail setup on the gateway for my internal network. Mails going out from internal to the Internet shows the following two Received: lines and I want to remove the internal IP on the second Received: line.

Received: from pen.ese.com (6-4-6-4.adsl.snet.net [6.4.6.4])
by atl4mhib39.myregisteredsite.com (8.14.4/8.14.4) with ESMTP id r9OFixjT014615
for <test@gmail.com>; Thu, 24 Oct 2013 11:45:00 -0400

Received: from mac (mac [192.168.0.17])
by pen.ese.com (8.14.3/8.14.3/Debian-5+lenny1) with ESMTP id r9OFYID7014798
for <test@gmail.com>; Thu, 24 Oct 2013 08:34:20 -0700


I found the Header Received: line in sendmail.cf, and I think that if somehow I can check the incoming mail IP, which is ${if_addr}, if equal to 192.168.0.x then just change the line to shows only the internal network number (192.168.0.x) instead of the full internal number. Can anyone have any idea on how to do this?

There is a way to call a rule set such as
HReceived: $>my_rule_set_1
Smy_rule_set_1
R ......

But I really don't know to do the conditional check. I imagine that there is something I can do such as:

if ${if_addr} = 192.168.0.17 then ${valid_send_addr} = 192.168.0.x
else ${valid_send_addr} = $_

And then the header line would be like:
HReceived: $?sfrom $s $.$?{valid_send_addr}($?s$|from $.d${valid_send_addr})
$.$?{auth_type}(authenticated$?{auth_ssf} bits=${auth_ssf}$.)
$.by $j ($v/$Z)$?r with $r$. id $i$?{tls_version}
(version=${tls_version} cipher=${cipher} bits=${cipher_bits} verify=${verify})$.$?u
for $u; $|;
$.$b


Any idea?

What you're proposing to do is against the mail RFC's as both sending and receiving MTAs need to record the route. And nobody is going to do anything with LAN range IP addresses anyway unless you run services that mistakingly allow for unrestricted recon or access. So what's the reason for mutilating mail headers?

Originally Posted by unSpawn What you're proposing to do is against the mail RFC's as both sending and receiving MTAs need to record the route.[] So what's the reason for mutilating mail headers?

We do this within our production environment as (generally) the servers generating the mail will use at least one, sometimes two relay servers before the mail exits the "production" platform. We strip the internal "hops" to remove any outgoing clues to our production architecture.

I just feel too exposing when people see what's on the internal network. That's all! No hidden agenda, just defending.
So if you know how, can you show me?

Originally Posted by TenTenths We do this within our production environment

Then by all means you should be the one to educate Softwiz.

Originally Posted by unSpawn Then by all means you should be the one to educate Softwiz.

I would, but I'm not at the office, couple of days holiday for Halloween / wedding anniversary