how to stop using *telnet <domain> 25*

[David A. Bandel]

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On Sat, 24 Jan 2004 12:00:15 -0600
Gary <gv-list-linuxsxs at mygirlfriday.info> wrote:

> On Sat, Jan 24, 2004 at 12:43:57PM -0500 or thereabouts, Bruce
> Marshall wrote:
> > On Saturday 24 January 2004 12:29 pm, Ben Duncan wrote:
> > > I think the question here is :
> 
> > > Someone outside our network/domain is using a telnet to
> > > port 25 to use the MTA.
> > >
> > > Anyone more familiar with iptables know if such a "service"
> > > can be blocked ?
>  
> > Assuming you need to have port 25 open to the outside world, then I
> > think you're left with blocking that IP address.   Yes, iptables can
> > block the address.  I do it all the time with shorewall.
>  
> > > Bruce Marshall wrote:
> > > > On Saturday 24 January 2004 10:57 am, Swapana Ghosh wrote:
> > > >>I ?have already blocked that IP. But the question is they can
> > > >use another>IP, which they did before already once IP with
> > > >different net work. So how>many IPs we will block? That is why i
> > > >was wondering , if there is a way>then we can stop our tension
> > > >for ever..
> > > >
> > > > I was going to say  "get rid of the telnet client"  since no one
> > > > really should be using it for anything...  but...   a) There
> > > > might be a need for it, or b) he might already have a copy of
> > > > the client (or could easily get one).
> > > >
> > > > Is there any clue as to who it is?   In the mail sent?
>  
> If they are using port 25, and you have an MTA running, sendmail,
> postfix, or qmail.  You should set your MTA to allow use for only your
> existing internal IP range, and you will not have this problem.. They
> will not be able to send mail period. 
> 
> In short, you have not properly closed down your MTA, and you are an
> open relay. 

Not exactly.  If the addresses the spammer is sending to is on that mail
server, then of course it has to accept the mail (not 100% true, you can
block IPs that don't reverse or resolve as mail servers -- I use
milter-sender to do this).

Ciao,

David A. Bandel
- -- 
Focus on the dream, not the competition.
		Nemesis Racing Team motto
GPG key autoresponder:  mailto:david_key at pananix.com
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