Subject: draft-delany-nullmx-00.txt good? bad? ugly?

From: wayne <[email-masked]>
Date: Tue, 14 Jun 2005 03:58:05 -0500

The following I-D has been floating around on the various anti-spam
lists: 

http://www.ietf.org/internet-drafts/draft-delany-nullmx-00.txt

Basically it proposes that people should publish records such as:

example.com.      MX  .

This would signify that example.com never receives any email.

Looking at the I-D, I can't see where it mentions the impact on the
root name servers caused by software that doesn't understand this
special convention and goes off and tries to do an SMTP connection to
them.

-wayne

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From: Chris Thompson <[email-masked]>
Date: Tue, 14 Jun 2005 11:37:29 +0100 (BST)

> special convention and goes off and tries to do an SMTP connection to

They wouldn't do that, surely? They would try to look up A (and maybe
AAAA) records records for ".", find there aren't any, and do whatever
their MTA does in that situation ("ignore the MX record and fall back
on the A/AAAA record for the mail domain name" being one obvious
possibility, which would subvert the intention of the I-D).

The NODATA result for the lookup(s) should be cachable by sufficiently
clueful nameservers, but it certainly doesn't seem like a desirable
thing to have happening.

-- 
Chris Thompson
Email: [email-masked]

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From: Peter Koch <[email-masked]>
Date: Tue, 14 Jun 2005 12:39:43 +0200

wayne <[email-masked]> wrote.

> This would signify that example.com never receives any email.

this is another bad example of publishing explict "NO" data points, although
in this case it is based on too liberal decisions in the past.

> special convention and goes off and tries to do an SMTP connection to

First, as an operational matter this might be better discussed on the DNSOP
list. Second, it's not SMTP connections that would cause a traffic increase
("." does not have any A/AAAA RRs associated with it, so there's no address
to connect to), but the additional section processing that would try to resolve
addresses for ".". These resolution attempts would not (or not only) happen in
the MTA but also in the name servers. Adding logic to MX handling that
deprecates ASP for specific targets, "." in this case, doesn't seem convincing.

-Peter