Andy takes a stab at asserting that SPFish syntax is enough, writing:
My first stab is:
+a:zzz/hdr-feedback-bulk=monitor(_at_)ibm(_dot_)com
or
+a:zzz/feedback-policy="dns:feedback.ibm.com?class=TXT"
Of course, there are problems here. In his first try, he says (by
example) that you concatenate the various modifiers together, separated
by "-". But the limits are immediately apparent: The
"=monitor(_at_)ibm(_dot_)com"
really modifies "feedback", but is stuck after "bulk" which is unrelated
to "feedback".
Furthermore, someone pointed out that we'd never really want to receive
a reply message for *every* matching message. So a publisher would
probably also need to stick a "p=.001" (send feedback with probability 1
in 1000) somewhere in there, and it's not obvious where. Andy's fist
example stops well short of showing that it's easy to extend SPF syntax
to get there.
His second example might be somewhat more promising. I assume that it
means "go resolve the URL "dns:feedback.ibm.com?class=TXT", and you'll
find something that gives the feedback policy. Of course, it immediately
begs the question of which URL schemes are allowed (dns? http? gopher?
ftp? mailto?) and what the format and language of the fetched document
is (XML? something else? TBD?)
To add more fuel to the fire of how hard it is to design a new language
with extensibility, nobody has yet noticed that Andy's examples, as well
as all of mine, are bogus: SPF already reserves the '/' character for
other purposes.
-- Jim Lyon