I don't have specific data, but since ADSP is so controversial and no
third-party authorization mechanism has been endorsed so far, my
guess would be that there are only two possibilities: ESPs are
signing using their own domains to sign, or ESPs have customer key
space delegated to them one way or another. I don't have hard data
about which is more prevalent, but we're definitely seeing both in
the stats reports I'm getting now.
I see three approaches by ESPs: mail signed signed by the ESP's own
domain, mail signed by a per-client subdomain of the ESP's domain,,
and mail signed with a delegated client subdomain. We could easily
write a BCP about them, but I don't think there's any point since it'd
be utterly uncontroversial, and it appears that everyone who needs to
understand it already does.
The mailing list arguments are all about discussion lists like this one
where there are multiple message originators with no connection to the
list itself other than being subscribers.
R's,
John
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