We know spammers' “known good ”address lists are anything but
Enter obviously bogus addresses into your blacklist with spamdb -T
$ spamdb -T -a "<firstname.lastname@example.org>"
Send email to <email@example.com>, you get trapped for 24 hours.
Few if any false positives; repeat offenders stay in.
Makes a real dent in the spam not caught by greylisting.
Used by Bob Beck at University of Alberta to generate an excellent, public blacklist.
NOTE: Publishing your greytrap addresses feeds known bad addresses back to harvesters; see eg http://www.bsdly.net/~peter/traplist.shtml and http://bsdly.blogspot.com/2007/07/hey-spammer-heres-list-for-you.html