$0.01 is just arbitrary. Some people might find that too expensive, and some spammers might find it cheap enough to profit from anyway. The problem is that the

$0.01 is just arbitrary. Some people might find that too expensive, and some spammers might find it cheap enough to profit from anyway. The problem is that the threshold for affordability is in NO way attached to the profit margins of spammers, let alone the true value of the email. And your last point is really just a specialized form of a web of trust anyway.