Yahoo announced yesterday they wanted to introduce a paid for email service to reduce spam. The idea is that each time you send an email you pay 1c to charity. The theory is sound, up to a point, but then unfortunately it falls down badly. The problem is that it is optional, and as soon as someone decides they don’t want to opt-in, it wont work. It would have the same effect on legitimate companies as well. Legitimate email marketing, newsletters and subscriptions to groups would very quickly become too expensive and either the cost would have to be passed on or email would stop being used.”]
Source: https://nakedsecurity.sophos.com/2009/08/18/yahoo-cent-mail-stop-spam/