That's one of the reasons why greylisting used to be effective; when a mail-delivery is attempted you give it a soft-fail, disconnecting the sender. The expect

That's one of the reasons why greylisting used to be effective; when a mail-delivery is attempted you give it a soft-fail, disconnecting the sender. The expectation is that by the time they try to deliver a second time you'll get "spam" results if you query DNS-based blacklists, etc, as other people have reported it already. These days greylisting doesn't seem to be so useful, as >50% of the spam I receive is sent from gmail/yahoo/similar. Hosts too big to block (sigh).