IETF Logo Mail Archive

Re: [spfbis] RFC7208 4.6.4 Interpretation - MX Lookup Count Inconsistencies

Jan Schaumann <jschauma@netmeister.org> Mon, 23 January 2023 04:05 UTC

Return-Path: <jschauma@netmeister.org>
X-Original-To: spfbis@ietfa.amsl.com
Delivered-To: spfbis@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id B805DC14F6EB for <spfbis@ietfa.amsl.com>; Sun, 22 Jan 2023 20:05:57 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.096
X-Spam-Level:
X-Spam-Status: No, score=-2.096 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_ZEN_BLOCKED_OPENDNS=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001, URIBL_DBL_BLOCKED_OPENDNS=0.001, URIBL_ZEN_BLOCKED_OPENDNS=0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=netmeister.org
Received: from mail.ietf.org ([50.223.129.194]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id dHsx7jB1RZka for <spfbis@ietfa.amsl.com>; Sun, 22 Jan 2023 20:05:52 -0800 (PST)
Received: from panix.netmeister.org (panix.netmeister.org [166.84.7.99]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id B099FC14E515 for <spfbis@ietf.org>; Sun, 22 Jan 2023 20:05:52 -0800 (PST)
Received: by panix.netmeister.org (Postfix, from userid 1000) id 5AA5F85861; Sun, 22 Jan 2023 23:05:53 -0500 (EST)
DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=netmeister.org; s=2023; t=1674446753; bh=32HjFjC/Eo7427hZcvi5HD+FgyZ0/GGcSO9lgMhl5e8=; h=From:To:Subject:Content-Type:From:To:Subject; b=qNgYfgEPjo/o0A8ehyzR/uT62KMIzw5MhwVYtWM/IMzcsQj2Kmf6rYnA0rTDNwlG1 QYdCSjRWZwDa734U0FiALbpQdy+chJtHNBUkIFsaa7gmum3dMtoMrrnx/Cv2gN2jJE wxdXuFGpw+oQhewQf+r+AtiCcdwfe+yMOVuikSZstJ6NVpurdIddODX3yhJSLzbxaj 4+cFO7fATSlcFp7r3/vWZQF6CuHqseQdxqUrjwNykb7+DXmtHUvOor6s7UPwrx0B8T +jOOuyYi3Rg5BuYV3QD24tDPBw8pl9eV6Jwx6XUw5OFioSe5+D9t4hS/cw2Qt62pSH fqID4eAJB44HQ==
Date: Sun, 22 Jan 2023 23:05:53 -0500
From: Jan Schaumann <jschauma@netmeister.org>
To: spfbis@ietf.org
Message-ID: <Y84HoTXeVZVMOlfk@netmeister.org>
Mail-Followup-To: spfbis@ietf.org
References: <79ac443e-b0ee-6598-cec0-9cf32c3dc1d1@tekmarc.com> <4155095.WaQZGZ3z5Y@localhost> <Y8SJjkQTFZO/Id/Z@netmeister.org> <13078447.edrPyRMrsX@localhost> <CADyWQ+FRgUPOC3OiMZ74kbD9Mn+r=Z51meY7uTZutfAJDr6ssQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <CADyWQ+FRgUPOC3OiMZ74kbD9Mn+r=Z51meY7uTZutfAJDr6ssQ@mail.gmail.com>
Archived-At: <https://mailarchive.ietf.org/arch/msg/spfbis/VQ2errf2nt6FHEs22d66RIoCoi0>
Subject: Re: [spfbis] RFC7208 4.6.4 Interpretation - MX Lookup Count Inconsistencies
X-BeenThere: spfbis@ietf.org
X-Mailman-Version: 2.1.39
Precedence: list
List-Id: SPFbis discussion list <spfbis.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/spfbis>, <mailto:spfbis-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/spfbis/>
List-Post: <mailto:spfbis@ietf.org>
List-Help: <mailto:spfbis-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/spfbis>, <mailto:spfbis-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 23 Jan 2023 04:05:57 -0000

Tim Wicinski <tjw.ietf@gmail.com> wrote:

> I also feel that technology stacks have matured over time.  Jan, do you see
> real world examples
> of a domain with 11 MX servers?

I just happened to be looking at the MX records for
the top 1M domains for other reasons, and counting
domains that have > 10 MX records, I find at least 265
domains.

The winning price goes to the apparently rather aptly
named domain 'everymailbox.com', with 398 MX records.
Second prize goes to 'preciseify.com' (266 MX
records), 3rd to 'rm02.net' (235 MX records). :-)

Those are obviously rare outliers, of course.

But I'm actually less concerned about domains with >
10 MX records (since the RFC seems reasonably clear
here to immediately fail), and more worried about
domains that have close to 10 total lookups, but where
counting the lookups resulting from turning MX results
into IP addresses would bump them over the limit of
10.

As illustrated by Mark's initial mail (and my own
misunderstanding), there are implementations that will
lead to such domains' SPF records as being marked
invalid when they shouldn't be.

(The last time I looked at SPF records of popular
domains[1], I found >8K domains with >10 total
lookups.)

-Jan

[1] https://www.netmeister.org/blog/spf.html

v2.23.0 | Report a Bug | By Email