A simple technological solution that email providers could introduce (if they were so minded) was suggested a few years ago - set up a 100 millisecond 'dead space' between sending copies of any email. If you're just sending a few, or even a couple of dozen copies, it would hardly notice, but if you're sending out hundreds of millions of the things your computer could be locked up for hours - and time is money.

Any bets on how long before someone introduces it?

Andrew