In particular, the social resistance to pay-by-unit systems applies,
and the micropayment infrastructure impossibility applies (and even
more so, because you're positing one micropayment infrastructure per
stamp vendor, so you get less economy of scale).
I agree on the social resistance, which is why I proposed the
proof-of-work stamps (which involve a non-monetary expenditure) to go
alongside it. I'm afraid the micropayment argument doesn't hold water,
because you can always pay for blocks of, say, a thousand stamps at a
time, and exactly how hard is it to keep track of one counter per
paying customer?Furthermore, the money paid for stamps goes to the wrong place, ie, not
to the recipients. (Stamp vendors could in principle pay recipients
who get mail with their stamps. This involves creation of _another_
micropayment infrastructure per stamp vendor.)
Good point. There's a way around this, though - how about the
recipient's stamp vendor collects a portion of the stamp's value from
the sender's stamp vendor, and credits it to the recipient's account?
If accounting is kept at both ends, then actual money would only change
hands relatively infrequently - in blocks, just like the sender pays
for the original stamps. But, this does require some kind of business
relationship - perhaps via an intermediary to help it scale - between
the two vendors.In a recipient-driven scheme, senders still have to be able to buy
stamps, but they will be able to choose their stamp vendor, rather
than being limited to their ISP.
Except that they have to choose a vendor acceptable to the recipient.
Keeping track of which recipients demand stamps from which vendors will
be another cost which you don't seem to have mentioned. If there are a
large number of stamp vendors it rapidly becomes almsot intractable.
If there are a relatively large number of stamp vendors, then they will
be differentiated into (roughly) two classes - trustworthy and
untrustworthy - depending on whether they give out free or subsidised
accounts to spammers or not. (Fair enough, some other factors will
probably come into play as well.) A relatively large number of vendors
also helps to open competition.