Re: SMTP spoofing ?

[Jon Lewis <jlewis () inorganic5 fdt net>]

On Thu, 19 Feb 1998, Perry E. Metzger wrote:

> John R Levine writes:
> > Are there any routers currently available that can do port 25 spoofing for
> > dialup users?  That is, when the user attempts to connect to port 25
> > anywhere, he in fact connects to port 25 on your own SMTP server instead. 
> >
> > In case it's not obvious, it's for spam management.
>
> It seems simple enough to block all outgoing SMTP to anything but your
> own server, and to apply such a filter on your dialups. I don't know
> if the more complex solution you propose is worth it -- the users will

Couldn't this be done with transparent proxy just as some ISP's do it for
web proxying/caching?

CONFIG_IP_TRANSPARENT_PROXY
  This enables your Linux firewall to transparently redirect any
  network traffic originating from the local network and destined
  for a remote host to a local server, called a "transparent proxy
  server".  This makes the local computers think they are talking to
  the remote end, while in fact they are connected to the local
  proxy. Redirection is activated by defining special input firewall
  rules (using the ipfwadm utility) and/or by doing an appropriate
  bind() system call.


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