I've had a bounce from a mimecast hosted domain that I don't
understand, and should be grateful for any help. I'm redacting
localparts, but nothing else.
The message is sent From: x...@btinternet.com, to a private mailing
list y...@bcrc.org.uk .
That list simply distributes the incoming message to the members,
using a MailFrom of yyy-requ...@bcrc.org.uk, and otherwise leaving all
headers unchanged apart from Return-Path, Received, and a private
X-SB-DKIM-Status header. The relevant incoming message has a valid
btinternet.com DKIM signature
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=btinternet.com;
s=btmx2012311; t=1725539173;
bh=urOLPb3Q/X5gx8ga5bbc2Wtt2iVG68mriPcqcbSGWKc=;
h=From:Mime-Version:Date:Subject:Message-Id:To:X-Mailer;
b=Wi/V5iktJPJtYQDx2bUaDokVYUsD++5KTZxp7+6NMZ7osfN6S9VkjstJ/6djJRaeYfmRHdVK2SwGIgVuhD/xzP8qQm1K9Vn9ARZL88kpalceLsm3A9/836IS3Gd8DOJEKAIY3C6mBwovXcGovtS1v1gV6Iza975s9NqxAkKaCEP3eNDfQTNo8MT+qVB33/RhnXdrC2SQxcmdgZr0ApvhW60yDHUS8eAKWdglYk/+h34it1mdYCYagrsETsdtOeEW4VDjoTuL5AGNtpgAJk/H89hz6EG85+EtV/tKF4nTH2hsD02cCDl03BNkaLwowniWSCjuUOTrCgdXnnvK7R/8YA==
One of the recipients is z...@thomasmore.co.uk, and that delivery
results in a bounce:
z...@thomasmore.co.uk
(generated from y...@bcrc.org.uk)
host eu-smtp-inbound-2.mimecast.com [195.130.217.241]
SMTP error from remote mail server after end of data:
550 DMARC Sender Invalid - envelope rejected -
https://community.mimecast.com/docs/DOC-1369#550 [Mx-vWL2qP5eCQ7y2fByS5w.uk156]
The help reference says that this means the SPF check in DMARC
fails. Well, of course it does, because the MailFrom is no longer the
From:. In fact, vanilla SPF passes, but the envelope is not aligned,
so it's not relevant for DMARC.
However, DKIM passes, as verified on the incoming message by my
server, so DMARC should pass.
What am I missing?
Thanks for any enlightenment!
Julian.
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