Hotmail, Juno, Aol...

How about using the email address as the hostage info? The goods are sent to the email address, so the sender knows that the email address is good. On breach of contract, the sender has the option of selling the email address of the reciever to a bunch of known spammers.

More rambling... ;)

-- Steve

P.S. If this particular contribution to your idea goes anywhere, I want credit. :)

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