On 2024-07-22 at 18:58:41 UTC-0400 (Tue, 23 Jul 2024 00:58:41 +0200)
Ralph Seichter via Postfix-users <ra...@ml.seichter.de>
is rumored to have said:

Adding *new* headers can't break existing DKIM signatures, because these
headers cannot have been signed before. New in this case means header
names (not values) which have not been present before.


This is not always true. Some systems are configured to "oversign" headers, essentially signing the non-existence. Any addition of headers that are oversigned will break a DKIM signature. Some ill-advised systems oversign List-* headers on every message.

--
Bill Cole
b...@scconsult.com or billc...@apache.org
(AKA @grumpybozo@toad.social and many *@billmail.scconsult.com addresses)
Not Currently Available For Hire
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