Greytrapping

Greytrapping is a new feature in OpenBSD 3.7 spamd. It allows you to specify spamtrap addresses that greylisted hosts may not mail to

A greylisted host that mails to a spamtrap address is removed from the greylist, and blacklisted for 24 hours. 

spamtrap addresses are added to /var/db/spamd with the spamdb(8) command

spamd automatically blacklists and un-blacklists offending hosts.