Paul -- quick note:
2. must not affect delivery(latency, integrity, cost, reliability) of
wanted messages to a point that would effect the normal use of email
I would suggest that a broken-out list of what "normal" uses of email are,
would be helpful here.
For example, difficult cases include
a. a small-scale, non-commercial mailing list, operating with confirmed
opt-in subscriptions. (not too hard, but pay-to-send solutions
could be problematic in such a use-case)
b. a user BCC'ing someone they've never met before (can look a lot like
spam to a naive content-based spam filter)
c. a user sending a mail via one ISP's SMTP server, with the rfc-822
"From" address set to another account on another ISP (quite
pathological, but it happens)
A few of the solutions already proposed may cause trouble for, or have
difficulty with, some of the potential use cases, so it'd be worthwhile
having a reference list of what the ASRG considers "normal".
For example, personally I would be happy with a solution that deals with
spam but breaks the c. case, since IMO it's a hack, and the old adage
about omelettes and eggs springs to mind. ;)
--j.
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