more specifically, money based sender-pays. None of these issues exist with proof of work stamp based sender-pays.To summarize the article, the following problems apply to sender-pays:
1. The Internet is global - "So implementing Sender Pays would require an international treaty".Postage in this case becomes an end to end protocol and not a cost of entry to a controlled access monopoly delivery service. All it would require it is private agreements for various issuers to settle accounts. If anything, there would be a strong need for government intervention to prevent monopolization of postage issuance as has almost happened in the certificate market.
quite true but since this is a closed domain not an issue.. Generating a coin is no problem. It is purchased from and cleared from the same source. also can be dealt with by settlement agreements between two issuers.2. "Micropayments remain a problem."
3. "Payment systems would have to be set up so that innocent parties wouldn't be stuck covering the cost of other persons' e-mails. Probably everyone would have to pay some amount in advance to cover the mail we might send."think bearer instruments. Mail will not be accepted without a valid coin. No need for book entry.
4. "by adding a cost to a message, Sender Pays would certainly impact the free e-mail business. Such services would have to decide whether to pass the costs along or pick up the tab."not necessarily. using a bearer instrument, the service is not an originator of the postage but merely passes it along. One could also have an account of postage coins with the e-mail service so one could send e-mail while they are on the road and no longer have access to their stamp pad.
5. "Here's another interesting problem: allegations have been made that there are Internet worms and other attacks that create an open proxy for spammers on an infected system" - "While this particular form of hijacking is built on old-fashioned SMTP, it would still suggest that Sender Pays will require that we first solve the open proxy problem—yet another difficult issue."proxy relaying will have no impact on sender pays systems. They still have to have a stamp of some form in order to be delivered. The real problem is a worm that gets into your system and takes over your e-mail client and sends lots of mail to mailboxes in Nigeria. If you compromise 300,000 hosts (like they did last time), it only takes $3.50 per machine to give you $1 million. ka-ching!
[1] this is a SWAG number. It's a gut feel based on how long you will let a double spending event persist and allow Spam to traverse filters.