There are some updated stories floating on the net regarding Yahoo!'s Centmail: "a charitable twist on the old idea of email postage stamps." where users donate $0.01 to a charity of their choice for each email they send.
Similar schemes like Microsoft's Penny Black or Hashcash have investigated other methods of stamping the email and use CPU cycles to measure the effort of the sender. Since there are about 80,000 seconds in a day, a computational "price" of just ten seconds per message would limit a spamming computer to at most 8,000 messages daily. So spammers would have to invest heavily in hardware in order to send high volumes of spam.
Very recently, during a meeting with one of my French partners, they also asked about Centmail, what my thoughts are on this and if it would be a good investment for them? In todays economic climate (and natural catastrophes happening around the globe), giving more money to charities is a good and noble investment to make... but less profitable. Paying an additional $10 per CPM is a very high price to pay to get your emails delivered.
Personally, I am more in favor to see every email marketing company (or any company for that matter) donate a % of every sell the make to charity - wouldn't that be just fantastic!?
Paying to get delivered - if things were only that easy.
Schemes that are saying "pay us and we'll deliver" sounds like the Godfather Vito Corleone making you an offer you cannot refuse.
It is better to work on the root cause of what blocks your mail from getting delivered and work on your reputation as a sender instead of buying into a false identity.
Your clients deserve this and when you show them "respect", one day they will return you the "favor".