On 5 Apr 2004, Paul Vixie wrote:
that's why greylisting has been so effective -- to combat it the spammers would have to add the one thing they cannot afford: "state." see http://www.rhyolite.com/dcc/ for how to get started.
why is 'state' so hard to afford? they already have a list of email addresses to spam, and they already have compromised boxes -- those are the big costs for spammers. another byte of state per email address is cheap (or if you are clever, a single bit stored in the email address itself, which doesnt cost you anything). i see greylisting being effective only as long as it doesnt get widely deployed. as soon as greylisting starts having any impact on spammers, they'll start spooling -- and it is very cheap to do so. after all, just about everything on compromised boxes costs them nothing. and compromised are the source of 99.9999999% of all spam. -Dan