[Cryptography] email from strangers -->

[John Levine]

>For one thing, I could insist that all unsolicited email
>bear a payment of 49 cents (equivalent to US first-class
>postage) payable to me via some cryptologically-secure 
>e-payment scheme.  
>
>I promise not to collect the payment unless I actually
>read the message. ...

That's attention bonds, aka Vanquish.  See US Patent 6,697,462.

Also see my rant at http://www.taugh.com/epostage.pdf which explains
why epostage will never work.  I wrote it ten years ago but nothing of
importance has changed.

R's,
John