Why charging for email won't do what people want
One of the common suggestions for fixing the email spam problem is to charge a small (often nominal) fee for email. Ignoring all of the problems with implementing such a scheme, and ignoring all of the people who would be violently against it, we can ask an important question: would it actually work?
Let's turn that around and ask the reverse question: has charging for paper mail stopped paper mail spam? Clearly the answer is no; most people get lots of junk mail, despite the senders having to pay for it.
Senders are willing to pay to send their junk mail (and to distribute fliers and so on) because the response rate is worth it. Since contemplated rates for email are at least an order of magnitude smaller than postal costs, charging for email can only avoid spam if response rates to email campaigns are vastly lower than for regular bulk mail ones, and I see no reason why that would be so.
(The other way to look at it is to ask what organizations would pay in order to reach people. For example, at one tenth of a cent per email, it's only $100 to reach 100,000 people; this is chump change to a marketing campaign. At that level people will spend the money just to see if their latest idea works out.)
The one thing that charging for email would do is kill off ISP level spam filtering, because no one is stupid enough to pay ISPs to accept email and then let them just throw it away. If organizations have to pay for sending email, they're going to rightfully insist on actual delivery and so all of your spam filtering is going to have to move to your client; ISPs will become much more like the postal service, stuffing your mailbox with anything they've been paid for.
You can also expect the rates to go up. Once they have to deliver all email, no ISP is going to charge less to receive it than their actual costs, and I suspect that the fully loaded costs are more than a tenth of a cent per email.
In short, charging for email commercializes it. Once it's commercialized, you can expect the interests of the people paying the money, ie the people sending email, to take over. And, as always, the interests of the people sending email are not the same as the interests of the people receiving it.
(You would get a different sort of email spam as a result of this; much more from DMA members, much less from discount pharmacies promoting potency aids.)