jms1 at jms1
Jun 12, 2008, 9:45 PM
Post #3 of 8
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On 2008-06-12, at 1631, Robert - elists wrote:
>
> Since I have been playing with Xen virtualization per JMS1's web
> directions
> at
>
> http://www.jms1.net/xen/
>
> I have found it to be quite excellent and interesting.
virtualization doesn't really have any bearing on your question, but
thanks for the plug just the same.
> If we have an example domain like with DNS mx records
>
> example.com IN MX fake1.example.com
> example.com IN MX real1.example.com
> example.com IN MX backup1.example.com
> example.com IN MX fake2.example.com
these "records" are all missing priority numbers. are they all equal
priority, or ordered in some manner?
> to start - What would be the best way to setup a fake or real port 25
> mailserver that all it does is reject the smtp session with the
> appropriate
> error
don't. it's a waste of your resources. it won't make any difference to
a spammer, he dumps a million messages into his queue and goes out for
drinks with the neighbors.
> It is my understanding that an unpatched qmail will not retry other
> MX under
> certain circumstances.
as kyle explained already, if you have non-equal priorities, qmail
will start with the lowest priority and stick with that, unless all of
the hosts with that priority value fail to answer- in that case it
will "step up" and try a hostname which has a higher priority number.
if any hosts with the lower numbered priority do answer but fail to
accept the message, it will not "step up" to the higher priority
records.
> Now, what I am getting at is that I do not want any sending qmail
> server or
> any other smtp server software to get stuck and only try that ip
> address
> forever
then make sure that whatever SMTP service they end up talking to,
accepts the messages.
> Im thinking if using centos5 in Xen subdomains to have backup mail
> servers
> and some fake smtp servers too as a spam fighting tool and for data
> collection towards spam fighting
i don't see how a "fake SMTP server" is supposed to be a spam fighting
tool, unless you want to set up a honeypot and try to gather data on
what spammers are doing- and if you're going to do that, you need to
be willing to dedicate some bandwidth to it, have enough know-how to
analyze the data properly, and take the time to do it. otherwise,
what's the point?
===
the only possible thing i can think of might be this: create a
service, not connected to qmail, but listening on tcp port 25 of an IP
address which is NOT listed as an MX target for any domain name... the
idea being that if not A or MX records point to it, then the only
people who would ever try to connect to it are people conducting port
scans... which means those IPs are some of the ones from which you
don't want to accept email.
it might look like this:
#!/bin/sh
PATH="/usr/bin:/bin:/usr/local/bin"
exec tcpserver -vR -x /etc/tcp/deny.cdb \
x.x.x.x 25 /bin/true 2>&1
where /etc/tcp/deny.cdb is built from the one line ":deny". then watch
the log file for that service, gather the IPs which try to connect,
and add them to a private blacklist. (come to think of it, that's not
a bad idea... maybe i'll do that on my own server.)
as you can see, the only software requirements are daemontools and
ucspi-tcp. it doesn't need qmail, and it certainly doesn't need xen.
you can do this on any normal machine by adding a second IP address to
the existing interface- you don't need a separate box (or a separate
xen session, same thing.)
- --------------------------------------------------------
| John M. Simpson -- KG4ZOW -- Programmer At Large |
| http://www.jms1.net/ <jms1[at]jms1.net> |
- --------------------------------------------------------
| Hope for America -- http://www.ronpaul2008.com/ |
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