Re: [Asrg] What are the IPs that sends mail for a domain?

Ian Eiloart <> Wed, 17 June 2009 10:49 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id DBBF628C228 for <>; Wed, 17 Jun 2009 03:49:05 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -2.276
X-Spam-Status: No, score=-2.276 tagged_above=-999 required=5 tests=[AWL=-0.277, BAYES_00=-2.599, J_CHICKENPOX_31=0.6]
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id 86px1qrmHcQ5 for <>; Wed, 17 Jun 2009 03:49:05 -0700 (PDT)
Received: from ( []) by (Postfix) with ESMTP id 47DE33A69CE for <>; Wed, 17 Jun 2009 03:48:48 -0700 (PDT)
Received: from ([]:61330) by with esmtpsa (TLSv1:AES256-SHA:256) (Exim 4.64) (envelope-from <>) id KLDQ2T-00053C-9H; Wed, 17 Jun 2009 11:49:41 +0100
Date: Wed, 17 Jun 2009 11:48:49 +0100
From: Ian Eiloart <>
To: Anti-Spam Research Group - IRTF <>, Franck Martin <>
Message-ID: <>
In-Reply-To: <>
References: <9112777.1871245190785748.JavaMail.franck@iphone-4.genius.local> <>
Originator-Info: login-token=Mulberry:010NWbuDk2CR0RQu8aPPtDSg4rNk28EjP7RUA=;
X-Mailer: Mulberry/4.0.8 (Mac OS X)
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
X-Sussex: true
X-Sussex-transport: remote_smtp
Subject: Re: [Asrg] What are the IPs that sends mail for a domain?
X-Mailman-Version: 2.1.9
Precedence: list
Reply-To: Anti-Spam Research Group - IRTF <>
List-Id: Anti-Spam Research Group - IRTF <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Wed, 17 Jun 2009 10:49:06 -0000

--On 16 June 2009 19:17:41 -0400 Daniel Feenberg <> wrote:

> I predict that no significant amount of mail ever originates from IPV6.
> Because it would be impossible to maintain a DNSBL for IPV6, I expect
> that enough sites will decline all IPV6 mail that it won't pay to send
> from it.
> Consider that because a spammer could (spoof) a different IPV6 address
> for every message, even a different 48 bit block for every messages, MTAs
> will be left with only content analysis for spam blocking.

Which is why reputation services need to be based on sender domains, not IP 
addresses. Users can then whitelist as required, and use of IP 
addresses/domains without good positive reputation won't work very well.

The advantage of IPV6, of course, is that you'll never have to share an IP 
address with someone with poor reputation.

> I don't expect
> IPV4s will ever be so scarce that enough MTAs will start using them out
> of necessity - ISPs will give each customer 4 IPV4 addresses with their
> million address IPV6 range, and customers will use those 4 addresses for
> the things that really need IPV4 - such as internet facing MTAs.

Ian Eiloart
IT Services, University of Sussex
01273-873148 x3148
For new support requests, see