Kee Hinckley said:
When you propose a change to the mail system that *requires* a
protocol (either through two supporting MUAs, or one supporting MUA
and one annoyed human :-) you are making a very fundamental change to
how email works. You have introduced a dramatic new level of
complexity. The difference between drop-and-forget and a real
protocol with bi-directional communication is huge. Most
importantly, it introduces a whole new way for things to fail.
FWIW, I *strongly* agree with this. It totally changes the semantics
of mail.
Here are a few to consider--independent of whether we're talking
hashcash, sender-pays, challenge/response, or anything else.
- initial message isn't delivered
- initial message is delivered to wrong person
-- intentionally (person left company, new person replies)
-- intentionally (I'm on vacation, forwarded my email to secretary)
-- unintentionally (something went wrong)
-- unintentionally (new person at ISP using old email address)
- protocol reply isn't delivered (gets lost somewhere)
- protocol reply is delivered late (lost in email)
- protocol reply is delivered late (back from six month vacation)
- protocol reply is misdelivered (see above misdelivery cases)
- protocol reply bounces (no account, mailbox over quota)
- protocol reply gets temporary bounce (host unavailable)
- protocol reply bounces without body in reply
- protocol reply gets on-vacation message
- protocol reply is sent return-receipt requested
I'd add
- protocol reply is sent to an address intended only to receive errors
(e.g. automated mail generated by notification component of an
e-commerce system)
--j.
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