The Red Cross or [insert your fave charity here] set up a 'deposit_email_ID' identity server. A deposit of $5 is required per ID, and a float of $150-$300 will do for the average user.
All email administrators can accept emails with validated Red Cross IDs, via a web service at which all emails can
be verified at the source using the unique ID.
Now, I'm an evil spammer. I pay my $5, or $5,000 for 1,000 ids and start spamming. Any user who reports my spam (using the ID number from the Red Cross) back to the server gets the deposit 'donated' to an international aid package. Reporting is known as 'flipping'.
Here are the rules that avoid work-arounds:
1. You have 4 days to report spam, after this time the ID returns as a credit to the sender's system. This is why $150-$300 should be enough of a 'float' for most users -- they keep getting fresh IDs to burn from their 'pool'.
2. If you 'report' an ID, then that sender will never be able to send a validated ID to you again unless YOU the RECIPIENT pay $100 to the charity. Why? Well, if you get mad with your boss and 'penalise' him by forcing a $5 Red Cross donation on him, he'll be happy to know you have to pay $95 to charity for being reckless, and $5 extra to reimburse the sender, just to get re-instated as a recipient of Red Cross IDs from that user.
Yes, a spammer could just pay $5,000 to send out 1,000 emails, but would they? Is that cost-effectve advertising? And wouldn't it be nice to receive spam knowing that each unwanted email was 'giving' $5 to charity?
Yes, I could 'close the deal' on an eBay auction by 'flipping' the seller's email address (knowing I don't need, nor want, another email from that person). In this case, the seller probably has little recourse for getting the $5 back. Over time you might pay about $70-$80 dollars a year on charity due to 'reckless flippers', but, well, it is a tax deduction, and don't you feel better?