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

Bill Cole <> Wed, 17 June 2009 05:13 UTC

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Date: Wed, 17 Jun 2009 01:14:02 -0400
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Subject: Re: [Asrg] What are the IPs that sends mail for a domain?
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Franck Martin wrote, On 6/16/09 11:33 PM:
> Knowing that mail servers are not deployed on IPv6, what would it take to
> make all these requirements mandatory for IPv6 and start with a better
> infrastructure than on IPv4?

How do you make anything mandatory on the net?

RFC 821 is one of a handful of Internet Standards, and it is violated 
routinely by spammers and non-spammers for no better reason than that they 
never bothered to read it. That is possible because the major MTA's are 
functional when misconfigured (e.g. with a bogus name for EHLO/HELO use) and 
by default tolerate clients which violate standards.

The only way anything can be functionally mandatory for email transport is 
if major MTA's will not work unless configured to comply and by default will 
not interoperate with clients that do not comply. RFC's are great, but they 
do not enforce themselves. If the big freemail providers and sites running 
Sendmail, Exchange, and Postfix generally accept mail from non-compliant 
clients, there will be a lot of non-compliant clients. To make good behavior 
mandatory, bad behavior has to break with enough frequency that it's easier 
to comply than negotiate exemptions.

> ----- Original Message ----- From: "Bill
> Cole"<> To: "Anti-Spam Research Group -
> IRTF"<> Sent: Tuesday, 16 June, 2009 8:27:27 PM GMT +01:00
> Amsterdam / Berlin / Bern / Rome / Stockholm / Vienna Subject: Re: [Asrg]
> What are the IPs that sends mail for a domain?
> Lyndon Nerenberg wrote, On 6/16/09 9:55 PM:
>> On Tue, 2009-06-16 at 17:24 -0700, Douglas Otis wrote:
>>> IMHO, all outbound MTAs should be required to return CVS records for
>>> their EHLO name and offer MX records for their inbound.
>> Doug, are you sure that's what you meant to say? The sentence is a bit
>> ambiguous. Are you really saying any host that sends mail (is an SMTP
>> client) MUST also host an listed SMTP server?
> I can't testify to what he meant, but I think what he is actually saying
> is that if you have a machine that says "EHLO" then there
> should be both a MX record for and a SRV record for
> (i.e. a CSV/CSA record).
> That doesn't mean requiring inbound SMTP on every outbound, it means
> requiring an affirmation in DNS that a name can be used in EHLO by a
> particular IP address and a way to get mail to the responsible party for
> the machine(s) using that name in EHLO. This is an admirable goal. A
> weaker goal would be to get people running non-spamming mail servers to
> follow the existing accepted standard of using a valid resolvable FQDN in
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