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Ralph Seichter macports-ml at
Thu Nov 3 00:08:44 CET 2016

On 02.11.16 23:58, Gabriel Rosenkoetter wrote:

> I may be mistaken, but doesn't passing mail through an intermediate
> mailing list (not just normal STMP routing) inherently invalidate your
> source SMTP server's DKIM signature?

No, it does not, if the mailing list is configured correctly. DKIM
signatures are created for a subset of headers and the message body at
the sending MTA. As long as MTAs along the route don't modify the data
but only add headers -- which is the correct behaviour -- signatures
remain valid. That's exactly what DKIM is about.

Modifying content however invalidates the signatures. For mailing lists,
this typically happens when the subject lines are rewritten, or, as in
this particular list, footers are added to the body. The footer is not
only unnecessary because it does not add any information that is not
present in headers anyway, it is actively harmful. DKIM is used in DMARC,
and if domains use specific quarantine/reject policies based on strict
DKIM alignment, the messages will not propagate.


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