On Fri, 16 Oct 2009, hector wrote:
How does a receiver know that the client is sending list mail? Do they
need to look at some other 2822/5322 header?
In many cases, they don't. Then they have to treat dkim=except-mlist as
dkim=unknown. But they lose nothing from the existence of dkim=except-mlist.
But *I* can treat dkim=except-mlist as dkim=all, because my mailserver is
programmed to specifically recognize the six mailing lists I am subscribed
to, by their bounce addresses.
In theory, a spammer could forge them, since none of them (not even
spf-discuss!!) use SPF. But guessing which list to forge is an SbO that the
spammers have not pierced yet.... Impersonating any list other than those 6
is futile -- it will bounce off my anti-Bcc filter.
Loosely, you could say that dkim=except-mlist is equivalent to dkim=unknown
when the validator is a big ISP, and equivalent to dkim=all when the
validator is a vanity domain.
But you don't need to be a vanity domain to *advertise* except-mlist, and
us vanity domains would appreciate it if you do.
---- Michael Deutschmann <michael(_at_)talamasca(_dot_)ocis(_dot_)net>
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