On Wed, 5 Mar 2003, Keith Moore wrote:
> Consider: To receive DSN notifications, the spammer can expect to
> receive between 10-20% of all the mail he sends out. Sending
> 1,000,000 messages to different addresses is cheap. Receiving 100,000
> to 200,000 copies of that same message to a single address (or even a
> few addresses) is not.
so the spammer pays that price once to clean up his list, and after
that, he only gets a few bounces back each time.
I believe that even that one-time price is sufficiently high to deter
a lot of spammers.