[Mimedefang] MX ->

Steffen Kaiser skmimedefang at smail.inf.fh-bonn-rhein-sieg.de
Tue Sep 13 08:29:10 EDT 2005

On Tue, 13 Sep 2005, Kenneth Porter wrote:

> --On Tuesday, September 13, 2005 1:29 PM +0200 Steffen Kaiser 
> <skmimedefang at smail.inf.fh-bonn-rhein-sieg.de> wrote:
>> Well, the same effort in to detect "bad" MX hosts can be performed by
>> ratware, hence, this technique can last for short while only, perhaps the
>> usefullness is gone by now.
> The 2nd best solution is to use "black hole space" for the last MX, IP space 
> guaranteed to not have a host. This ensures that the spammer has to time out 
> the connection. But it means that the timeout is only as long as the stock 
> TCP SYN timeout.

Good point.

> An even better solution is to point to a host that tarpits port 25 
> connections. Such a host accepts the connection, but then turns the TCP feed 
> into a trickle, effectively forcing the spammer to tie up the connection 
> forever. (You can install a netfilter module on Linux called "TARPIT" for 
> this purpose.)

You still have to ensure that any of the "good" MX hosts must be online 
all over the time. Or at least ignore / tempfail connections, when all the 
other hosts are down.


Steffen Kaiser

More information about the MIMEDefang mailing list