Great Circle Associates List-Managers
(September 1996)

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Subject: Re: Blocking Domains
From: jeffw @ smoe . org (Jeff Wasilko)
Organization: Jeff's Personal System
Date: Sun, 8 Sep 1996 14:27:17 -0400 (EDT)
To: marym @ Finesse . COM (Mary Morris)
Cc: List-Managers @ GreatCircle . COM
In-reply-to: <199609081706 . KAA00898 @ thyme> from "Mary Morris" at Sep 8, 96 10:06:51 am

Mary Morris writes:

> Can anyone see a reason to not use firewall techniques to refuse
> a connection to port 25 from specific systems or domains? By refusing
> connection to a known email transit point, email can be denied
> without ever receiving it to examine it. This of course does nothing
> to the good domain with one bad user. I use a piece of software
> called TCPD which refuses connection to any host in a hosts.deny
> file for services. 

The problem here is that the spam source can simply direct the mail via
an innocent third-party system, which will (most-likely) accept it and
then forward it to you. The TCP connection will then be from a
different host than the one you are blocking.


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