Dec 062010

This time i’ll show you how to randomize your smtp outbound’s IP addresses. This can be done via transport map. But, since ordinary Postfix lookup tables store information as (key, value) pairs. it will provide static value only. we need someting that can manipulate the value (right hand side) of a lookup table. In order to answer random transport value.

first come to mind was tcp_tables, tcp_tables lookup table gives some flexibility for us to execute our tiny perl script that will randomizing transport. that’s the basic idea.

Ok, here’s the first part, create perl script call, anyway this script only provide answer in “catch-all” manner. so it will randomized, all outgoing mail.

# cd /etc/postfix
# vi
#!/usr/bin/perl -w
# author: Hari Hendaryanto <hari.h -at->

use strict;
use warnings;
use Sys::Syslog qw(:DEFAULT setlogsock);

# our transports array, we will define this in as transport services

our @array = (

# Initalize and open syslog.

# Autoflush standard output.
select STDOUT; $|++;

while (<>) {
        # randomizing transports array
        my $random_smtp = int(rand(scalar(@array)));
        if (/^get\s(.+)$/i) {
                print "200 $array[$random_smtp]\n";
                syslog("info","Using: %s Transport Service", $random_smtp);

	print "200 smtp:";

Make it executable

# chmod 755 parts

Run the scripts via postfix spawn daemon service. inet  n       n       n       -       0      spawn
          user=nobody argv=/etc/postfix/

add 5 smtp client services called rotate1, rotate2, rotate3, rotate4, rotate5, that bind to its own ip
address and has uniq syslog/helo name.

# random smtp
rotate1  unix -       -       n       -       -       smtp
          -o syslog_name=postfix-rotate1
          -o smtp_bind_address=

rotate2  unix -       -       n       -       -       smtp
          -o syslog_name=postfix-rotate2
          -o smtp_bind_address=

rotate3  unix -       -       n       -       -       smtp
          -o syslog_name=postfix-rotate3
          -o smtp_bind_address=

rotate4  unix -       -       n       -       -       smtp
          -o syslog_name=postfix-rotate4
          -o smtp_bind_address=

rotate5  unix -       -       n       -       -       smtp
          -o syslog_name=postfix-rotate5
          -o smtp_bind_address=

Before we actually implement our randomize transport, let’s make sure that the setting actually work.

Reload postfix

# postfix reload

Run this query fiew times, and you’ll see the perl script will return “random answer” transport

# postmap -q "whatever" tcp:
# postmap -q "whatever" tcp:

And so on..

Note on “whatever”, since the script acted in “catch-all” mode as i’ve mentioned earlier, what ever postfix transport_maps client asked. it will be answered with random values such as rotate1, rotate2, rotate3, rotate4, rotate5 in randomized fashion. parts

Add these lines

transport_maps = tcp:[]:2527 = 3600s

Reload postfix
that’s it. example log would be like these and that’s indicate that randomizer is working.

Month date 12:26:53 host postfix-rotate1/smtp[4252]: A1CA68480A4: to=<>,[]:25], delay=3.6, delays=0.69/0.01/0.81/2, dsn=2.0.0, status=sent (250 ok dirdel)
Month date 12:27:06 host postfix-rotate5/smtp[4253]: 41C2E8480A4: to=<>,[]:25], delay=6, delays=0.14/0.01/0.85/5, dsn=2.0.0, status=sent (250 ok dirdel)
Month date 12:27:22 host postfix-rotate3/smtp[4277]: 4BA9F8480A4: to=<>,[]:25], delay=7.9, delays=0.85/0.02/0.61/6.4, dsn=2.0.0, status=sent (250 ok dirdel)

I’m not taking any responsible if the reader “misuse” this tutorial.the tutorial is provide as-is for experimental purposes.

use Sys::Syslog qw(:DEFAULT setlogsock);

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