Cor Bosman via mailop skrev den 2026-10-13 13:04:
Hi all, we’ve noticed that outlook is returning 4xx for forwards with a
valid DKIM because there is a duplicate signed header. Usually a
Mime-Version header.
Microsoft now verifies the mime structure before DKIM so these fail
DMARC despite a valid DKIM. We’re seeing this with pretty large senders
like TikTok, Volkswagen, and many others.
How do other people deal with this? “Sender problem”?
eq mailop.org
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mailop.org;
s=2026-rsa; t=1791889535;
bh=8lzzIsi57iluUnQzASmuDKH+LmhCpRHdFL6hW5cT37Y=;
h=Mime-Version:Date:To:Subject:List-Id:List-Help:List-Owner:
List-Post:List-Subscribe:List-Unsubscribe:From:Reply-To:
Content-Type:Content-Transfer-Encoding:Autocrypt:Cc:
Content-Transfer-Encoding:Content-Type:Date:From:In-Reply-To:
Mime-Version:Openpgp:References:Reply-To:Resent-To:Sender:Subject:
To;
b=kqdleK9C87G36qmb0w0C9hOhZgYqYC00ASfp8rxU7IXnGxjup7mV/rD5eYVK3l7P0
D7/uX6/+jYt4XEEAPyiICaMVd5gKxoN/hGCRVnDH5J0u3EaFLPnnSCl1Ne0WqQkpCm
NsNbn8M2R2C9hfJT3+VCfY2b1EDTPZMZry1KhFemDFjxs1Qj+kadjBo0GIZrvAByTv
mJPFZGaZpXNaHuxZ+GTU9+2cro4EC7y0Po0hAXpHnJBLK05fnb2B41PJ3dpSmofiLJ
SPmhnPc3h66vYE4gZxAqO2og84fg0a4Of4/DDjiu88MoPJ9K19LXyDZqRuQWwnOPym
uDiiaL60T6mUw==
multiple To: signed
possible a bug in amavisd, not solved, also multiple other headers in
dkim
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