I think there's a disconnect between the spammer and the MTA trying to deliver the spam to me. I would gamble that most of the spam getting dropped of to me is done via someone unrelated third-party's MTA. Tarpitting that unsuspecting, dimwitted, ignoramus's MTA seems harsh as it doesn't draw the attention to their real issue.
Never send back a decline, only send back soft failures so it sits in their queue until it expires. Sure they keep trying to deliver it to me. Perhaps fire a squadron of 2M (some significant size that won't be auto-dropped) emails back at the MTA trying to slough off spam as legit junk and fill up their spool. Address each of those emails to a tarpitable email address on my server and I'll let those sessions time out and never deliver to me. It's like a sending in a missile that doesn't explode until it's well inside the walls. My $0.02. > If I can stall a few of these long enough.. perhaps the real server > behind the proxies will give up sooner (and possibly drop the email > address from its list?)... >
