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

Daniel Feenberg <> Thu, 18 June 2009 21:29 UTC

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Date: Thu, 18 Jun 2009 17:22:16 -0400 (EDT)
From: Daniel Feenberg <>
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Subject: Re: [Asrg] What are the IPs that sends mail for a domain?
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On Thu, 18 Jun 2009, Rich Kulawiec wrote:

> On Tue, Jun 16, 2009 at 11:36:37PM -0400, Bill Cole wrote:
>> That said, I think that adding DNS records that map specific network
>> addresses to their legitimate behaviors in a generalized model would be a
>> positive advance.
> +1.  For instance, I (semi-seriously, semi-facetiously) proposed "XM"
> records some years ago, whose value would be 0 or 1: hosts with 1 send
> SMTP traffic, hosts with 0 don't.  Thus every MX's behavior could be
> to reject all port 25 SMTP connections from hosts with XM=0.
> There a lot of problems with this idea, and if memory serves, both
> Dave Crocker and John Levine pointed them out at the time.  But I think

Are there problems that would extend beyond the problems of traders in 
improper material who don't want their material sitting in queues on the 
ISP MTA? This is usually dressed up as "The FBI is after me for my 
advanced political views" or "My ISP is an evil monopolist", but are there 
problems for other users of email?

I would also add that the "end to end" principle, however much it applies 
to voluntary associations between endpoints, can hardly be applied to the 
SMTP protocol, where complete strangers are expected to interact. Sites 
will always be cautious of strangers, and asking that SMTP senders be 
vouched for by their DNS providor is a very small concession indeed.

Furthermore, the "endpoint" in the "end-to-end" principle is a host, not
a user, so it is perfectly within the principle to is a host IP address as 
a discrimination device.

Daniel Feenberg