after some futile searching for a badmailto patch for qmail, i finally stumbled across the badrcptto patch. (i'm using this to reject messages to bogus addresses at php.net at the smtp level, rather than endure the inevitable deluge of double-bounces or just blackhole mail to those addresses.)

i guess i should really be looking at qpsmtpd, but i wanted to pick the low-hanging fruit first.